Screens & Sightlines

Introduction

Electronic display technology in learning and teaching has become increasingly widespread only since the late 1990s. Initially, presentation materials were prepared by experienced authors and the low resolution of displays inherently limited the production of content that was too small to read.

Today, the commoditisation of ICT means nearly every presenter uses a computer regularly and the vast majority now author their own materials – only rarely is a specialist graphic designer employed to assist.

The quality of contemporary display technology allows higher ambient light in teaching spaces and affords users the freedom to develop any materials they want.

At its very core, the role of AV in learning and teaching is to facilitate communication of ideas and information to an audience. The design of our display systems must support this by providing an environment within which appropriately prepared materials can be viewed and assimilated easily.

Our learning environments, and the display systems within them must then take account of:

  • The task itself and how display must support it; and

  • How our audience/users consume the presented materials

Screen based presentation and interactivity are a crucial part of modern teaching and learning practice. The content displayed can vary between courses but commonly includes:

  • Microsoft PowerPoint, Apple KeyNote and similar presentations

  • video content from DVD/Bluray, YouTube or other online repositories, and dedicated media players (including cinema quality)

  • websites

  • word processing documents, spreadsheets and other text-based applications

  • detailed graphs, charts, engineering drawings

  • fine arts materials – paintings, illustrations and other imagery

  • data visualisation and scientific modelling

  • medical imagery

  • virtual reality and visual representations of augmented reality

Viewing Standards

The key viewing standards that should be used for specifying display solutions in member organisations are:

AVIXA Display Image Size for 2D Content in Audiovisual Systems (DISCAS) - for screen sizing

ANSI/InfoComm 3M Projected Image System Contrast Ratio (PISCR) - for contrast ratio

Both make reference to viewing categories in order to assist with selecting the appropriate design parameters.

Viewing categories

The majority of environments encountered in the professional AV realm will meet one of the categories first defined in ANSI/InfoComm 3M Projected Image System Contrast Ratio. These four viewing categories are planned to be used by AVIXA for all future ‘image’ standards.

These are summarised as:

Type

Description

Passive Viewing

The viewer is able to recognize what the images are on a screen.

Basic Decision Making (BDM)

The viewer can make basic decisions from the displayed image.

Analytical Decision Making (ADM)

The viewer is fully engaged with minute detail present in the content and needs to be able to resolve every element of the projected image.

Full Motion Video (FMV)

The viewer is able to discern all detail provided by the cinematographer necessary to support the storyline and inferred meaning.

Passive Viewing

The viewer is able to recognize what the images are on a screen and can separate the text or the main image from the background under typical lighting for the viewing environment. The content does not require assimilation and retention of detail, but the general intent is understood. There is passive engagement with the content (e.g., non-critical or informal viewing of video and data).

This is a minimally acceptable contrast ratio, primarily for passive presentations or passively watching images on a screen.

Passive viewing environments are locations where images are displayed to an audience as a means of providing informal information. Business presentations may fall into this category if they are informally informational but not dependent on a high level of detail.

In a typical passive viewing environment, ambient light may be high and system contrast may be challenged by room features like task lighting, windows, bright (reflective) surfaces, or projectors with insufficient light output.

Basic Decision Making

The viewer can make basic decisions from the displayed image. The decisions are not dependent on critical details within the image, but there is assimilation and retention of information. The viewer is actively engaged with the content (e.g., information displays, presentations containing detailed images, classrooms, boardrooms, multi-purpose rooms, product illustrations).

The viewer should be able to understand what is being communicated. Graphic images and text are legible to the extent that the viewer can make basic decisions on the basis of what is being seen. Decisions made are based on comprehending the informational content itself and are not dependent on the resolution of every element of detail.

Basic decision-making viewing applications include the presentation of photographs, detailed graphic images, product illustrations and information displays such as airline departures, sports scores or stock quotes. In this scenario, the information obtained from the projected image informs a basic decision by a fully engaged viewer.

In a typical basic decision-making environment (e.g., classrooms, multi-purpose rooms, board rooms), there may be some degree of ambient light control, such as window shades and zoned task lighting.

Analytical Decision Making

The viewer is fully engaged with minute detail present in the content and needs to be able to resolve every element of the projected image. Analytical decision-making environments support professional assessments, such as the examination of medical imaging, engineering or architectural drawings, electrical schematics, photographic image inspection, forensic evidence or failure analysis.

Analytical decision-making viewing environments typically have controlled ambient light – particularly on or by the screen – often with darkened or anti-reflective surfaces and highly focused task lighting.

The minimum system contrast ratio for analytical decision-making was determined to be 50:1. The task group observed that, in practice, although achievable, close attention to both the system design and environmental characteristics will be necessary to achieve the desired contrast.

Full Motion Video

In this category, movies or other full motion videos are projected in a controlled viewing environment with an audience that has a high level of engagement with the content. The viewer is able to discern key elements present in the full motion video, including detail provided by the cinematographer or videographer necessary to support the story line and intent (e.g., home theater, business screening room, broadcast post-production).

Most home theaters and business screening rooms would fall into this category.

To test this viewing requirement category, film historians selected scenes from critically-acclaimed commercially available movies on DVD and Blu-ray to illustrate important levels of detail that can only be perceived with adequate contrast ratios. The evaluation content included classic scenes from Alfred Hitchcock’s North by Northwest, Christopher Nolan’s The Dark Knight, and many others.

Initially the task group was not told what to look for in a scene, only to respond to something they had not noticed in a prior viewing (i.e., when the system contrast was set to a lower level). As in the other categories, ambient light was adjusted to generate image contrast ratios.

Specialist Spaces

Specialist spaces should always be designed to reflect the specific requirements of that specialism. Whilst specialist spaces may not be formally covered by the AVIXA categories, the principles remain informative. Examples of specialist spaces include:

  • Cinemas should be designed to SMPTE or other industry criteria

If also used for non-cinema screenings, a lecture theatre should have projection and lighting which is configurable to achieve AVIXA’s Full Motion Video requirements, as well as the required non-cinema functionality.

  • Professional medical imaging analysis (compared to training spaces, eg. DICOMM)

Specifying Image Size and Ceiling Heights

To enable what’s displayed on-screen to be successfully viewed by the entire audience, the content must be of an appropriate size to both the nearest and furthest audience member.

Consequently the determination of the screen size must not be an arbitrary decision based on the physical dimensions of the space, but rather a result of careful consideration of viewing requirements based on current industry standards.

Purpose-designed spaces in the modern era should be designed with appropropriate ceiling heights to allow sufficiently sized screens. Where the ceiling heights of legacy spaces cannot be modified and are insufficient to allow appropriately sized screens, alternative options must be considered to achieve viewing standards (and often this can incur higher costs).

The acceptable area for audience placement in front of a screen is determined by:

  • the horizontal and vertical angle of view

  • the distance to the display for the closest and furthest viewers

  • the nature of the content being displayed

These factors must also be determined in conjunction with the following information and not be defined in an ad-hoc manner.

Previous AETM rule for screen sizing

Traditionally there has been an AETM rule associating the recommended screen height to the maximum viewing distance, being:

The height of the projection screen or flat panel display shall be no less than the distance from the centre of the screen to furthest audience member divided by 5.3

This is still a good rule of thumb, but with the rapid changes in display technology and resolution in recent years, alongside recent industry-developed standards, a more dynamic approach to screen-sizing based on the required viewing category and human vision can be leveraged.

Our industry’s focus on developing standards helps us all produce better, user-centred systems by defining clear ground rules which can be communicated to the design team.

Importantly, some of these standards allow customisation by each institution to best suit their users, audiences and activities.

Presenting Multiple Simultaneous Content

In many educational organisations the presentation of two independent images is now a standard requirement for medium to large presentation spaces. Independent dual display systems allow educators to present complementary information, for example a PowerPoint presentation on one screen and a document camera on the other.

It is possible to achieve this using a single large ultra-high resolution (4K or above) display, however costs and system design will need to be considered.

Screen Aspect Ratio

AETM recommends projection in either the 16:9 or 16:10 ratio as this better matches modern film and television programming and compliments the output of wide screen laptops and material such as spreadsheets. Presenter slides can usually be converted between 4:3 and widescreen formats, although care must be taken to preserve the integrity of the content (eg. in MS Powerpoint, the layout, text placement, fonts, format and shapes).

The compliant viewing area

Current standards don’t specifically define a compliant room; rather they allow you to define the compliant viewing area as being within closest and farthest viewer distances and the horizontal viewing limits.

In real life, floor space is expensive and sector-wide or institutional space metrics are applied to create construction budgets and inform the architect. It is rare for every seat in every space to be within the compliant viewing area, but it should always be the target.

Each institution should document the criteria within which project design teams (architects, space planners, system designers, etc.) must operate, defining:

  • Institution-specific element height or other parameters

  • What proportion of viewing positions must be within the compliant area for the design to be accepted

Best practise would be for 100% of seats to be within the shaded area:

However, by mutual agreement in some circumstances it is possible to define the farthest viewer distance as sacrosanct but allow some seats closer than the standard allows.

You will need two numbers, to cater for both those spaces with just one image and those where multiple discrete images are displayed.

Example: It is common for an organisation to require compliance ratios of 90% for single image systems and 80% for multiple discrete images. This is a pragmatic compromise and is broadly applicable to new rooms and refurbs. However, it is always worth keeping in mind that students in the ‘cheap seats’ will have a compromised experience.

When defining or updating your internal design guide, remember those closest to the image may get a sore neck or find that the image occupies such a large portion of their personal field of view that they need to turn their heads in order to assimilate information.

The AETM recommends that you work closely with your Facilities Management team to agree on physical environment standards that meet technical and budgetary constraints, and you have those principles mandated by your institution’s design standards.

Partial Conformity

The AETM recognises that site conditions, heritage considerations, and other factors sometimes cause difficulty with full compliance to all of the rules for screens listed below, especially during refurbishment projects.

Meeting the recommendations is often most difficult for those audience members seated closest to the screens. Teaching spaces typically fill from the back, with front rows more likely to be empty. Consequently if compromise regarding a rule is unavoidable, then it is preferable that the rules compromised relate to vertical viewing angles (which will primarily affect the closest viewers) rather than the maximum viewing distance versus display size rule (below).

Agreement in writing for any compromise must be obtained from the AV designer and the AV staff representative of the organisation.

Viewing Distance and Sightlines

The farthest viewer, horizontal and vertical sightlines defined by the AVIXA standard are based largely on human factors as an outcome of research. The specification of these angles provides clarification of the ‘best practice’ design principles.

Farthest Viewing Distance

One of the most important factors to consider when sizing a presentation system is the farthest viewing (FV) distance. It is this parameter that ultimately sets the height of a display system, often one of the most difficult items to coordinate in a teaching space.

Horizontal Viewing Angle

This is all about considering geometric distortion of displayed information. Once the viewer is more than 60° off-axis this distortion is typically unacceptable. The aim of designers is to make it easy for viewers to assimilate information so we must avoid unacceptable geometric distortion.

Note: when multiple images are displayed this 60° angle is measured from the farthest vertical edge of the farthest image.

Vertical Viewing Angle

Scientific research indicates that comfortable head movement only falls within ±30° of the horizontal. The maximum vertical viewing angle is then 30° above the eyeline of the closest viewer.

Whilst we do not specifically define the closest viewer for Analytical Decision Making (ADM) spaces, the rules of geometric distortion and viewer comfort still apply. In an ADM space, viewers are expected to self-select their viewing position to afford themselves an appropriate view.

In Australia and New Zealand we typically design for a ‘standard’ eyeline around 1200mm (seated) or 1700mm (standing) but this will not apply if you’re designing a space for children.

Most countries publish detailed anthropometric data about their own population, and your architect or space planner will have access to it. Especially when designing for an overseas campus, check the local data to set your design parameters.

Screen Sizing based on Viewing Category

Note that for calculation of image size, only two categories are considered:

  • Analytical Decision Making (ADM): In those areas where pixel-level detail must be resolved (e.g: some fine arts, medical imaging, engineering spaces.)

  • Basic Decision Making (BDM): Everywhere else. Most learning and teaching spaces are categorised as BDM

A space may be categorised as both ADM and BDM, although the compliant viewing areas of the space will be different for each scenario.

AVIXA have a useful calculator that can be used to determine the appropriate screen size based on your organisation’s requirements:

https://www.avixa.org/standards/discas-calculators/discas

The remainder of this section contains information to assist with understanding the factors involved in sizing a screen appropriately for a given viewing task or category.

Understanding Element Height

The majority of spaces in contemporary institutions will be categorised as Basic Decision Making (BDM) and to specify images we must determine the size of the smallest element you wish to be able to resolve under typical conditions. This is called the element height and is the height of the element expressed as a percentage of the total image height (%EH).

We cannot control the quality of user-authored presentations, so each institution must determine an appropriate image height through observation and investigation. The %EH may differ between institutions, and will be partially informed by less tangible parameters:

  • If instructors typically display complex diagrams, images or text you might oversize images to improve readability.

  • Viewers may be able to assimilate very complex materials given sufficient time and the ability to focus – but remember that they are also listening to the instructor.

  • Existing spaces may have been designed decades before the advent of presentation technologies, and the local architecture may constrain the size and location of screens.

A good starting point is a minimum element height of 3%, which fits neatly with previous industry standard practice that called for the farthest viewer distance to be no more than 6x image height.

For those organisations wishing to retain a 5.3* Image Height (IH) multiplier, the element height as a percentage of the overall image is 2.65% (often expressed as %EH = 2.65).

Example

Understanding Text

An element can be graphical or text, but many designers want to translate it to font sizes as a frame of reference. This section is not an authoritative discussion of typography – any font is characterised as much by the white space as the black as well as several other artistic decisions – but provides a basic understanding of text construction which may be useful.

An electronic character is typically defined within a minimum of a 9 x 7 pixel grid:

However an example of the smallest character only requires 5 vertical lines of pixels:

When considering element height, consider how your user will resolve unscaled text (which is covered in the next section) that may only be five pixels tall.

The average human eye can generally resolve only down to one minute of arc (one sixtieth of one degree). Always consider how that will translate to providing a workable viewing distance.

For members of the audience who are visually impaired it is possible to share content via software-based tools directly to their personal devices. This must be based on pedagogical decisions and is not for architectural or technical staff to decide. It should not be used as a guideline when designing physical spaces.

Scaled vs Unscaled content and why it is important

Until recently, the maximum affordable display resolutions still allowed comfortable viewing of all materials with little forethought. The rapid adoption of higher definition displays means we must now consider the type of content more closely.

  • Applications like PowerPoint, image viewers and similar maximise the content to fit the screen – this is scaling and is entirely transparent to the user.

  • Text and line-based applications generally present exactly what you tell it to, and will not second-guess you to improve your presentation.

Consider a typical spreadsheet. First a screen grab at 1080P:

and exactly the same document but at UHD (“4K”) resolution

A great deal more information is presented, but assimilation is much more difficult – if you were reading from any significant distance it may be impossible. Excel, along with word processors and other scientific modelling software, are non-scaling applications. Unless magnification is applied by the user, everything is rendered at native resolution.

For text, if you ignore the white space above and below the character, typical fonts appear to be at one pixel per point So an 11-point letter will appear as 11 pixels tall, regardless of the resolution you select.

To continue the example, at 1080P, that 11 pixels equates to just under 7mm tall on a typical 55” display, but:

  • approximately 10.4mm tall at 720P

  • only 3.5mm tall at 4K

Always consider unscaled applications when designing your display systems. Regardless of the native resolution of the display, you should externally scale your system resolution to a value that still allows users to navigate the desktop and viewers to read some content. User-applied magnification may still be appropriate, but users still need to be able to resolve the image well enough to get to this point.

Presentation System Resolution

Presentation system resolution has been progressively increasing in density ever since the advent of digital display technologies. The viewing standards discussed in this chapter are applicable across display resolutions, and an organisation must consider the system resolution it standardises on system resolution and the best option must be selected based on all of the factors influencing the decision. 1080P has become the most commonly used, though some applications will require either higher or lower resolutions.

When designing a system it is important to factor in the effects of down-scaling to a resolution that is lower than what is native to the display device. This can have a negative effect on the final image quality, for example it is possible that a 1080P PC output could look soft, pixelated and ugly on a native 4K display, just as a 1080P image can when downscaled to 720P.

Traditionally, best practise has always been to match the resolution of the source to the display to achieve the best picture quality. However, things are no longer quite so simple.

Just as manufacturers have phased out 720P flat panel displays, 1080P native displays will go down the same route, with 4K displays being the standard offering. With projector technology still continuing to support lower resolutions natively (and at lower price points) as well as a variety of aspect ratios, video signal management and processing must be carefully considered in each system deployment.

This translates to matching the available sources and output devices to a common resolution that is compatible with both (and suitable for the viewing task), and ensuring that the signal processing infrastructure supports the required AV signals. In practice, this can often prove difficult without the benefit of EDID management, and consideration of the end-to-end system bandwidth.

Contemporary routing systems may allow you to change this scaling on the fly so you can trigger a change to 4K for DVD playback or back to your default for unscaled text. You should test this with a variety of source devices before considering deployment to production systems.

Ultimately the best results will be achieved by setting up a ‘test rig’ to confirm the design works in practise, using the actual devices selected for the system. By taking advantage of the instrument of measurement which is the best judge of what looks good to the human eye - the human eye itself - you can determine categorically whether the image quality is acceptable.

BDM only: Sizing the image

To specify an image correctly, we require three pieces of information:

  1. Image height (IH)

  2. Farthest viewer (FV); and

  3. Element height (%EH)

A constant called the Acuity Factor (AF) helps simplify our calculation, and this is defined differently for ADM and BDM. AFBDM = 200 and is the result of simplifying complex trigonometric calculations.

With any two of the three variables and the acuity factor we can determine the missing variable and adequately size the image. The formula is straightforward, and easy to manipulate to find the missing variable.

To calculate Image Height (IH):

IH= FV%EH x AFBDM

Rearranging the formula lets us to find the Farthest Viewer (FV):

FV=IH x %EHx AFBDM

or the Element Height (%EH):

%EH= FVIH x AFBDM

For example, if:

  • Image Height (IH) = 1500mm

  • Farthest viewer (FV) = 10500mm

then:

  • %EH = 10500 / (1500 x 200) = 0.035 = 3.5%

But a percentage means nothing – just how tall should my ‘element’ be?

Good news! You can easily define absolute element height (let’s call it |EH|) by manipulating the same BDM formula.

Consider a presentation compromising a single element occupying the full image height. It follows that:

  1. %EH = 100% (0.01 for the formula)

  2. As the element is full height, then |EH|| = IH

Our formula, then becomes:

EH=IH= FV1 x AFBDM, so:

|EH|= FV200 and FV=|EH| ×200

BDM only: Defining the closest viewer

We have discussed that the closest viewer in a BDM space should not angle their head more than 30° above horizontal to view the top of the image, so can apply the standard trigonometry tangent function to determine the closest viewer distance; i.e. the length of the adjacent side of the triangle.

tan = oppositeadjacent

In this example:

  • angle (α) is 30°; and

  • the length of the opposite side is the sum of the Image Height (IH) and its offset with relation to standard eyeline (IO).

Substituting for our terminology and rearranging delivers a dramatically simpler formula:

tan 30° = IH + IOCV

CV= 1tan 30° × (IH+IO)

= 1.732 × (IH+IO)

For example, if:

  • Image Height = 1500mm

  • Bottom of image = 1400mm; and

  • Standard eyeline = 1200mm

then:

  • IO = (1400 – 1200) = 200

  • CV = 1.732 x (1500 + 200) = 2944mm

Width of the Front Row (CVROW)

It is useful to also calculate the maximum width of the front row, which is naturally constrained by our eye’s useful horizontal viewing limits of 60°. To avoid ambiguity, we abbreviate this term to CVROW.

CVROW =6 ×IH+IO-IW

Using our example above for a 16:9 image:

  • IH + IO = 1500 + 200 = 1700

  • IW = 16/9 x 1500 = 2667

  • So CVROW = 6 x 1700 – 2667 = 7533

You should use this value to check your work when plotting the viewing area – if it doesn’t match what you’ve drawn you’ve made an error!

ADM only: Sizing the image

In ADM we are looking to interrogate the finest detail of the displayed image, so the element being examined is an individual pixel. The calculation must then consider the size of the pixel – so we must include vertical resolution in our calculation.

Our variables for ADM, then, are:

  1. Image height (IH)

  2. Farthest viewer (FV); and

  3. Vertical image resolution (IR)

A constant called the Acuity Factor (AF) helps simplify the calculation, with AFADM = 3438 and is a result of simplifying quite complex trigonometric calculations.

The closest viewer for ADM is defined only by the horizontal limits of a display system, so image offset is not considered. Your screen should be sited to afford viewers an opportunity to self-select a comfortable viewing position.

As with BDM calculations, the formula can be rearranged to solve for whichever is the missing term, so to calculate Image Height (IH):

IH = IR ×FVAFADM

Rearrange the terms to solve for Farthest viewer (FV):

FV= IH ×AFADMIR

Rearrange again to identify required minimum Image Resolution (IR) for a given IH and FV:

IR= IH ×AFADMFV

For example, if

  • Image Height = 1500mm

  • Vertical image resolution = 1080 pixels

then

  • FV = 1500 x 3438 / 1080 = 4775mm

AVIXA publishes calculators online at: https://www.avixa.org/standards/discas-calculators/

Drawing the compliant viewing area

You must be able to clearly communicate the compliant viewing area to the architect and other stakeholders during the design phases of any project. Whilst all modern construction will be modelled in Revit or an equivalent package, speed and accuracy of communication are the key and you will normally be marking-up the latest architectural layouts.

Drawing the compliant viewing area seems daunting at first, but after a bit of practice you should be regularly preparing accurate, informative markups in just a couple of minutes – using nothing more complex than your favourite PDF tool.

This section provides an example which demonstrates a simple strategy for markup using Bluebeam, a commonly used PDF tool for engineering. For simplicity this exercise is drawn over a blank sheet rather than a busy architectural layout.

As with all design, accuracy is important – but it’s ok not to stress over a few millimetres. No two heads will usually be in exactly the same position, and even 100mm at FV is within expected head movement range.

You need to complete your design calculations first – for this example, we’ve calculated as follows:

  • 120” projected image at 16:9 aspect ratio

  • Bottom of image = 1400mm AFFL(i.e.: Image Offset = 200)

  • Element height (%EH) = 3.0%

  • FV = 8970

  • CV = 1.732 x (1495 + 200) = 3109

  • CVROW = 6 x (1695 + 200) = 7515

Item

Description

1

Draw the screen to scale and in its expected position

2

Using the ANGLE tool from the Measurements tool group, add the 60° horizontal viewing limits

3

Measure CV from front of screen and add a horizontal CV line

(Cross check your work by measuring CVROW – if it is incorrect, check whether you correctly calculated including Image Offset)

4

Using the CENTRE RADIUS tool (Measurements tool group), draw circles with radius of FV. Position a circle at each end of your screen.

5

Select Bluebeam’s POLYGON tool and draw a closed line following this path

  • CV between its intersections with the horizontal limit lines

  • Along horizontal limit line to the intersection with the inner arc

  • To the intersection of the two circles

  • To the intersection of the inner arc and the horizontal limit line; and

  • Back to the intersection of the CV and horizontal limit lines

6

Right click on one of the FV lines and select CONVERT TO ARC. Manipulate the handles to shape the arc to conform to the inner circle. Repeat for the second FV line

7

Delete all construction lines – what remains is your compliant viewing area.

But what about a dual-image room? Simple.

8

Model the two screens individually

9

Add a second polygon to define the overall compliant viewing area. If all screens display the same image, the compliant area is as below

10

If each screen is independently routable, only the common area (union of the discrete compliant viewing areas) is valid

Technology-specific Recommendations

Projection Systems

Projector Placement

The height that a projector is positioned is dependent on a number of factors. Each projector has different optical characteristics and a manufacturers recommended vertical position in relation to a given screen size. To ensure a high quality image the projector must be installed in the manufacturer’s recommended vertical position.

Installation grade projectors often include a lens shift function that allows a range of vertical positions to be used. Traditionally, the highest position that a projector with lens shift can achieve is level with the top of the screen image area. More recently, manufacturer’s are producing variable lenses that allow even more flexibility. Furthermore, ultra-short throw fixed lenses are available that allow a much shorter throw distance, which by their very design necessitates mounting beyond the top (or bottom) of the projected image.

The use of electronic keystone to correct the optical aberrations caused by the improper placement of a projector is generally advised against, as electronic keystone will almost always degrade the clarity of the image.

The decision on the placement of the projector is also influenced by a number of other considerations:

  • ease of maintenance

  • lens throw distance

  • projector noise intrusion

  • ventilation

  • physical obstruction in the projector light path

  • the additional cost of telephoto or short throw (wide angle lenses)

  • security concerns

  • ensuring the presenter’s workable area in front of the screen is free from projector glare

Where the venue is equipped with a projection booth, the maintenance, security and noise reduction benefits of placing the projectors in a sealed room can be considerable, although will not always outweigh the simplicity of mounting the projector within the auditorium. In general terms, the noisier the projector, the more beneficial it is to have it acoustically isolated from the audience area. Always review the projectors datasheet for its operating noise level in the context of the ambient noise levels within the space.

Ventilation is an important factor and needs to be compliant with manufacturer recommended operating temperatures at all times, whether the projector is in a booth or the venue itself.

The use of projectors with a laser light engine can be a large factor when considering placement in relation to the ease of maintenance. Where a projector is in a hard to reach location a laser model would be ideal, but in easily serviceable spaces a lamp-based equivalent might present a better ROI, especially where lamps are still in stock as spares.

Factoring in physical intrusions such as room lights into the cone of the projected image is important. Also, the ability of the audience and the presenter to walk in front of the screen without contending with the glare from the projector in their faces is also an important element to be considered, with possible occupational health and safety implications. The closer a projector is to the screen the steeper the angle of light and the more glare-free work area is created. See the illustration below:

Projector position

This issue becomes even more critical for interactive whiteboard applications. Consequently a range of ultra-short throw projectors are available that overcome the problem.

Short throw technology is only suitable for a screen with a gain of 1.0 or less. When using a screen with a gain factor above 1.0 (for example in rear projection) screen manufacturers recommend that the projector be placed at a distance of greater than 1.6 x screen width (16:10) to avoid excessive angles of incidence which will cause brightness issues at the edges of the picture.

Projection Lens Selection Considerations

All data projector lenses will have an effect on the amount of light that passes through its construction, sometimes called the lens loss factor (LLF). The use of short-throw (wide) or long-throw (telescopic) lenses that provide additional versatility to installation options will typically come at the expense of reducing the amount of light that leaves the projector. As a rule of thumb, using a 20% reduction is often suitable, but for any critical and final calculations, always consult the manufacturer for the specific lens loss factors of a model, which vary between makes and models. Ultra-short throw lenses often can have an LLF of up to 40%, resulting in a need to significantly increase the power of a projector to achieve similar results.

Projection Surfaces

Projection should ideally be onto matt white, purpose manufactured projection screen material with a gain of 1 (gain is a measure of screen surface reflectivity). Screens may be fixed or retractable, depending on the needs for whiteboarding in the venue. Where high-gain or rear projection screen material is used, the manufacturer’s recommendations regarding optimum viewing angle must be followed.

Walls as Screens

Walls are acceptable as projection surfaces so long as they are painted flat (matt) white and are uniformly flat and perpendicular to the projector and the audience. Special paint is available for projection walls and may be specified by the standards of individual organisations. Wherever feasible, a fixed screen with a black border is preferred as it provides a high-contrast frame for the image which improves the perceived contrast of a viewer.

Whiteboard and Writable Surfaces

Whiteboards are generally not suitable for use as projection screen surfaces as the shiny surface causes unacceptable glare and hot-spotting. Where whiteboard surfaces are used in special circumstances (for example in interactive whiteboard installations) the projector used should be of the ultra-short throw type so that most glare is reflected away from the audience area.

Glass or highly reflective writing surfaces are not suitable to be used as projection screens.

Flat Panel Displays

Flat panel displays including those with 4K native resolution have become ubiquitous in the AV industry, thanks to their competitive price, high contrast image capabilities, multiple digital inputs and ease of integration across a broad spectrum of system types.

Many simple systems will require the use of a 1080P source that is matched with a single flat-panel display. As the display offerings become available in higher resolutions (4K+) only, it is important to use EDID management to scale down the resolution so that it is readable by users and remains cost-effective. Ideally this is able to be performed natively (through display settings), but often requires the use of external EDID management devices. The use of software resolution settings and text zoom may be suitable for a resident computer device with a managed SoE, but will not scale a user’s laptop video resolution for appropriate viewing when using an HDMI cable.

Remember that the screen sizing guidelines provided in this chapter and referred to in standards are suitable to find the appropriate flat panel display, at a known video resolution.

AVIXA has developed calculators for DISCAS (Display Image Size for 2D Content in Audiovisual Systems and these are available free online at: https://www.avixa.org/standards/discas-calculators/

Further information regarding the applicable formulae and examples can be found in the appendix.

Ultra High Definition Display Systems (4K, UHD or above)

4K UHD display technology is increasingly becoming available as a viable cost option in small to medium venues. The recommendations already stated in this chapter still apply, however it is worth noting that the larger the venue gets, the more problematic it is to achieve the minimum and maximum recommended viewing distances for the audience.

For example, often to meet the minimum element height requirements for readability of text using a 4K image you would need an extremely large screen area, which will in turn impact the minimum acceptable distance to the closest viewer; and thus make achieving the recommendation for this unfeasible.

Use of a single large 4K display instead of multiple displays would need to consider the individual screen areas and their resultant image size. Each window will need to adhere to the appropriate viewing standard.

However, the suitability of 4K (or even 8K) can also be content dependent. For example, if the display is only ever going to be showing pure video content, then 4K may be a viable or even desirable option. If mixed media is to be employed then it certainly will prove more problematic.

AETM recommends that where required, specialist advice is sought in this area when designing systems to display at 4K or above in projection environments.

Video Conference Venue Display Systems

The display technology in video conference venues is often required to perform the dual function of both video conference calls and presentations and should be sized using the guidelines above.

The cameras used to capture video conference images require higher lighting levels than generally needed for note-taking in lecture theatres and seminar rooms. Generally flat panel displays (such as LCD panels) are much better at coping with high levels of ambient light. Accordingly, large flat panel displays are the recommended technology for small and medium sized video conference venues.

Further information on videoconferencing may be found in later sections of these guidelines.

System Image Contrast Ratio

Viewers rely on displayed materials to communicate information in such a way that it can be assimilated correctly and efficiently in a way that supports their purpose.

No displayed image is defined by contrast alone, but it remains one of the most critical criteria. Without adequate contrast, text is difficult to read and colours are inadequately saturated.

When designing systems we seek to provide adequate contrast applicable to the task – and to replace years of ‘rules of thumb’ ANSI standards are being released:

  • ANSI/InfoComm (AVIXA) 3M Projected Image System Contrast Ratio (PISCR) was ratified in 2011; and

  • ANSI/AVIXA V201.02 Direct View Display Image System Contrast Ratio is in development

The four viewing categories that are used for other AVIXA vision standards were first defined in PISCR. In typical learning environments;

  • The majority of spaces will be characterised as Basic Decision Making “The viewer can make basic decisions from the displayed image. The decisions are not dependent on critical details within the image, but there is assimilation and retention of information. The viewer is actively engaged with the content (e.g., information displays, presentations containing detailed images, classrooms, boardrooms multi-purpose rooms, product illustrations).”

  • A smaller number of spaces will be Analytical Decision Making “The viewer can make critical decisions by the ability to analyze details within the displayed image. The viewer is analytical and fully engaged with these details of the content (e.g., medical imaging, architectural/engineering drawings, forensic evidence, photographic image inspection).”

  • Screening rooms and multipurpose lecture theatres may be categorised as Full Motion Video “The viewer is able to discern key elements present in the full motion video, including detail provided by the cinematographer or videographer necessary to support the story line and intent (e.g., home theater, business screening room, broadcast post-production).”

  • Passive Viewing will not generally apply as we are generally seeking more than “non-critical or informal viewing of video and data”.

Designers must always take care not to use PISCR or DVDISCR to supplant dedicated standards for broadcast and cinema (SMPTE), medical imaging (DICOM and others), photographic analysis or similar. AVIXA standards only provide performance criteria for these spaces in a typical ‘pro AV’ context.

Understanding the System Contrast Ratio

Put simply, we’re interested in designing for a human viewer, and not quantifying theoretical laboratory performance. The available standards define the contrast between the peak white and black levels under normal viewing conditions, including ambient light.

The system contrast system test pattern is the 16-zone checkerboard with alternating black and white areas which was developed in the early days of electronic projection. You don’t need an expensive test pattern generator for contrast – you can make it yourself in PowerPoint or any similar package

Don’t rely on the contrast figures quoted in projector/display manufacturer marketing materials. These numbers will be quite defensible (the Society for Information Display and the International Committee for Display Metrology published an extremely technical standard about display measurements) but describe the performance of the display under laboratory conditions. They have little bearing on a viewer’s experience.

For the four viewing categories, the required system contrast ratios are:

Category

PISCR

Passive Viewing

7:1

Basic Decision Making

15:1

Analytical Decision Making

50:1

Full Motion Video

80:1

‘Normal viewing conditions’ requires us to configure the house lights and blinds/drapes appropriately for safe movement and notetaking; and light any spotlights on the presenter. During the design process,

  • Negotiate your requirements with your Capital Works team so they can brief the design team adequately.

  • Engage with your lighting designer early and often – they may be able to influence the Architect’s luminaire selections and will definitely be able to predict the ambient light which will be incident on your displays.

  • Consider whether you need to conduct modelling to determine the impacts of daylight

Calculating the System Contrast Ratio

In order to design a compliant system we must be able to calculate the ‘brightness’ required to achieve the specified System Contrast Ratio.

Projection

Gather the following information:

  • Ambient light on screen (L) from all natural and artificial sources. This is realistically your ‘black’ level, as the system cannot achieve lower. Measured in lux.

  • Target contrast ratio (C)

  • Image area (A), which you can easily derive from the Image Size calculations you have prepared. Measured in m2.

  • Screen gain (Sg)

    • If you are using a typical vinyl or fibreglass projection surface, the screen should be unity gain (1.0) but maybe slightly above or below

    • Specialist screens – particularly ambient light rejection types will usually offer higher gain but have a smaller field of view

    • In all cases – ask the screen manufacturer for data if you are unsure.

  • Lens derating factor (Dl). It is often difficult to get accurate lens data so the following assumptions are made:

    • A ‘standard’ lens is one with throw ratio around 2.0 (in practice often 1.7-2.3) and which has the least complex light path; i.e.: fewest glass elements. Dl = 1.0

    • Short- and long-throw lenses generally contain more glass elements and are expected to lose 20% of the light. Dl = 0.8

  • Projector derating value (Dr) is applied so we achieve the required System Contrast Ratio on average across the life of the projector.

    • A new projector theoretically should measure 100% output, and with the end-of-life often considered 50% brightness then a calculation point of 75% brightness is reasonable. Dr = 0.75

    • Where eco or “constant brightness” modes are used “out of the box” as the default setting, the AETM recommends derating the light output a further 10% to account for age, dust and component wear over time . e.g ECO mode (80% light output) - 10% wear and tear equates to a Dr = 0.70

Once you have the requisite information, apply this formula to determine the minimum required projector brightness (Luminous flux, measured in lumens):

v=L×C×ASgDrDl

Example

  • Screen:

    • 120” 16:9 (2655 x 1495 = 3.97m2)

    • Standard vinyl; gain = 1.0

  • Ambient light on screen = 80 lux

  • Viewing category is BDM, target contrast ratio = 15:1

  • Standard lens

Then v=80×15×3.971.00.75×1 = 6352 lumens

If the options for selecting a projector to meet the criteria in the above example are a 6,000 lumen unit or a 7,500 lumen model, it is necessary to specify the projector with the higher output, as it meets the minimum contrast ratio requirement for the space. A good rule of thumb is that you should never under-specify a projector as this can have serious consequences to the viewability of the final image, and ultimately the usability of the space.

Measuring the System Contrast Ratio

We don’t often measure System Contrast Ratio following a new build – our design calculations and display settings should ensure compliance by a substantial margin. When evaluating/qualifying an existing room, however, a quick and reliable method of measuring is required.

Full details are contained in ANSI/InfoComm 3M, but the general process is simple and described here. It requires only two items of test gear:

  • A test pattern which you can build yourself in PowerPoint – a simple full-page slide made up of 16 equal rectangles which are alternately filled white or black.

  • A spot photometer/luminance meter with a narrow (<2°) acceptance angle. We want to measure reflected light (what the eye sees) and the narrow acceptance angle allows us to target an area right in the centre of each box.

    • Several devices are available, from hobbyist level to those designed for high level scientific use. For a typical institution AV team, a photographer-level devices is sufficient and offers the best value for money. However, ensure your meter provides measurements in units lux.

    • Ensure any test equipment is calibrated regularly. Most standards require calibration at no more than two-year intervals.

The actual procedure is straightforward:

Step

Description

1

Let your projector/display warm up for a few minutes so it is operating in its usual temperature range

2

Load the test pattern on a handy computer and display it full screen

3

Set room lighting and blinds/drapes to the normal default setting for projection

4

At each measuring location (refer standard) use your meter to measure the luminance in the centre of each of the rectangles. Record the results.

5

When measurements are complete,

  • Calculate the average of all the WHITE measurements

  • Calculate the average of all the BLACK measurements

  • Divide average WHITE by average BLACK to derive the contrast ratio at that positio

6

Repeat this procedure for different lighting presets in a multipurpose space (e.g.: general teaching and ‘screening’ modes)

Contrast Ratio Standard Compliance

To provide acceptable legibility for projected images, the contrast ratio (the difference between peak white and black in the projected picture) must fall within defined minimum limits. The contrast ratio achievable in a teaching space depends upon the brightness of the projected image (the ‘peak white’) and crucially upon the amount of ambient light falling on the projection surface (which determines the system black, or minimum level).

AETM endorses the ANSI/ICIA published specification regarding contrast ratios in projected images:

ANSI/INFOCOMM 3M-2011: Projected Image System Contrast Ratio

To achieve the recommendations of the AETM Design Guidelines, in spaces that use projected images the AV Designer and Lighting Designer must design AV systems and lighting systems to meet the ANSI/INFOCOMM 3M-2011 Projected Image System Contrast Ratio standard. Copies of the standard are available for purchase from:

In spaces where higher levels of natural ambient light are desirable, AETM recommends the use of an emissive technology such as flat panel displays, which inherently provide a higher system contrast ratio.

Application of the ANSI/INFOCOMM 3M-2011 standard in learning environments

In teaching space design, and in particular in lighting design, ambient light from all sources must be controlled so that the following minimum recommendations regarding contrast ratio are achievable at any point on the image area. Measurement must be according to the procedure outlined in the ANSI/Infocomm standard referred to above.

It is generally accepted that the 7:1 system contrast ratio is not suitable for educational environments, as the tasks carried out in these spaces would not be considered ‘passive viewing’.

In lecture theatres and other tertiary education presentation spaces the standard lighting preset for projected presentations must also provide workable levels of light for student note taking. This pre-set would correspond with the 15:1 system contrast ratio target and would typically be the setting called upon most commonly for general presentations. This viewing task is known as ‘Basic Decision Making’.

The next lighting preset in a lecture theatre often provides lower light levels in the space. The purpose of this pre-set is to provide the best quality of image possible while still accommodating note taking by students. The 50:1 contrast ratio targeted in this preset aligns with ‘Analytical Decision Making’ viewing tasks, such as the reviewing of engineering drawings and image inspection tasks.

The final pre-set in a theatre is usually reserved for the presentation of motion picture (cinema) content or similar material. An 80:1 system contrast ratio is the target for these purposes in an educational environment, often best achieved by turning all lights off, except for those required for safe egress within the venue.

The ANSI/INFOCOMM standard for contrast ratios may on occasions be difficult to achieve while at the same time providing sufficient light to illuminate the presenter and the students’ writing surfaces, however it is essential that it is achieved. All uncontrolled light that reflects off surfaces and spills onto display devices is detrimental to the system contrast ratio.

Light coloured floor coverings and furniture (including lecterns) near the projection screens should be avoided as much as possible since they will reflect significant amounts of light from the spot and stage lights onto the screens.

Basic Recommendations for Minimum Projector Brightness

As outlined previously in this section, to achieve best results we should always use accurate figures in the calculation of system contrast ratio to support specific viewing tasks, usually ‘Basic Decision Making’ or 15:1. However, it is sometimes useful to have a few quick and easy ‘rules of thumb’ to follow, which are outlined below. Note that these minimum requirements assume a ‘typical’ space which is not adversely affected by spill from artificial or natural light. The basis of the numbers below use an ambient light level of 45 lux.

It is always best to attempt to limit the ambient light spilling on screen before increasing the output power of the projector. The more you can lower the lux level falling on screen the better the results will be, because the system contrast ratio is the primary concern, and the lux rating on screen is merely a general guide.

Large venues require large screens, which in turn require powerful projectors. For example, using the inverse square law we know that a screen twice the width requires a projector 4 times as powerful to achieve the same brightness on the screen. ANSI lumens is a measure of light emitted by a projector and lux (lx) is a measure of light falling on a given area.

A common minimum target for projection is 500 lux for any given screen size. This target is usually achievable for small to mid-sized venues; however this is progressively more difficult to achieve in large venues without the use of expensive high-output projectors. For large venues sometimes it simply isn’t possible to achieve the full 500 lux minimum target, therefore any reduction below this target level will only comply with the ANSI contrast ratio standard if the lighting is carefully designed to significantly restrict ambient or spilled light falling on the projection screen(s).

The AETM recommends that for all spaces of more than 100 seat capacity the following process occur at the commencement of the detailed design phase:

  • The AV Designer provides the calculated lux values for the proposed projection screen and projectors solution to the Lighting Designer for sign-off.

  • The Lighting Designer provides for sign off by the AV designer the results of a computer lighting model of the proposed lighting design that confirms the achievement of the 7:1, 15:1 and 50:1 contrast targets mandated by the ANSI standard for contrast ratios.

As a general reference the table below provides a guide to the recommended minimum projector light output of lamp-based projectors. For laser engine projectors it is recommended to increase the output by 25% as their light output diminishes over time and the light source cannot be replaced.

Screen Size (16:10 Diagonal)

Screen Width

Screen Height

Projector ANSI

Lumens

100” (250cm)

2.15m

1.35m

>3000

120” (330cm )

2.6m

1.6m

>4000

150” (380cm)

3.2m

2.0m

>7000

200” (500cm )

4.3m

2.7m

>10,000

>200” (>500cm)

>4.3m

>4.3m

Specialist High Power

Notes: the figures above are based on standard (imperial) 16:10 screen sizes – the metric equivalents are approximate