Why use ALR screens?
ALR (ambient light rejecting) projection screens are used in hybrid meeting spaces to avoid asthenopia (‘eye strain’) and create optimum user experiences. Why?
The unfortunate truth is that eye strain is often designed into hybrid meeting and teaching spaces. It’s never intentional, but just reflects a general tendency for room lighting to be overlooked.
Do you design in or design out asthenopia (‘eye strain’) into your Teams Rooms and teaching spaces when specifying displays? This 100% essential step in the AV designer and consultant’s workflow is so easy - but usually overlooked.
In Microsoft Teams Rooms the Task Luminance Ratio should be limited to <3. What does this mean? OK. Here goes…
Our eyes are effectively cameras that feed video signal into our visual processing system. They are mechanical devices. The ciliary muscle continually expands and contracts to adjust the lens thickness to focus, plus regulate the pupil aperture to control the amount of light striking the retina. Working it too hard creates asthenopia, namely eye strain.
TLR (Task Luminance Ratio - ‘task’ referring to the object we see at any given moment) limits the ‘brightness’ (luminance, measured in cd/m2) of all key objects (screen, people, table top etc) within a certain range, a ‘luminance ratio’.
Continually glancing from dark to light objects (‘tasks’) gives your eyes an unneeded workout. By limiting Task Luminance Ratio to 3:1, it’s possible to create environments where people can work for extended periods without that fatigue. I use 2.5:1 to provide some tolerance.
Look at the spreadsheet below, using a typical Microsoft Teams Room scenario of 400 lux illuminance (‘ambient light’) falling on a table. I use this calculator to understand how to limit the brightness of the display.
Displays are usually too bright in hybrid meeting/teaching spaces - the primary cause of eye strain.
If we limit the brightness of the display, and we know the metric of image quality is contrast - the difference in white and black levels - then the only way to achieve good contrast is to reduce the black levels.
The only way to achieve deep black levels - and to have the image size that next-generation MTRs need (including Front Row 21:9) - is to use ALR (ambient light rejecting) projection screens.
Posted: 19th October 2022