Why “eye-gonomical” thinking?
To improve working environments by offering required image contrast with a balanced display brightness that will not stress and wear out users
The user situation (“What we really see”) is our benchmark – not the lab measurements.
The way that the human eye works must be taken into consideration when designing an optical system
The human eye is a very complex mechanism that can adjust to work in different environments. As an example we can read headlines in a newspaper by the light of the moon alone but we can also read the same newspaper in broad daylight on a sunny day.
The difference in ambient light level in these two situations is approximately 30.000:1 (0.5 ft-c and 15,000 ft-c).
How the human eye works
The reason for this incredible dynamic range of view is that the eye works with adaption levels. The eye constantly adjusts to the average light level in the field of view. Therefore you will experience momentarily blindness when walking out a dark room and into the sunlight. The blindness occurs while the eyes are adapting to the new average light level.
An important function of the eye is the fact that it works logarithmically. A clear difference in light is perceived by the eye when the brightness either doubles or halves.
Example: If an object has a luminance of 50 Ft-L the eye will only see a clear difference to another object if the brightness of this object is either 25 Ft-L or 100 Ft-L
Contrast is by definition the difference between what the eye sees as being black and white.
When it comes to contrast the human eye is a delicate instrument. The eye can work with a maximum contrast range in the field of view of 1000:1
This means: If there in the field of view are two objects: One with brightness 5 Ft-L and one with 5000 Ft-L. The 5 Ft-L object will appear completely black and the 5000 Ft-L object will appear completely white to the eye (5000/5 = 1000)
For this reason more than 1000:1 contrast ratio is needless. However, much lower contrast ratios are more than enough to give a good image.
Contrast and ”eye-gonomical” thinking...
The two most important factors when designing any kind of display installation:
The surrounding environment.
The function of the display:
- meeting room
- control room
- Home theatre
- Signage and advertising*
* In signage and advertising applications the function of the display is mostly to be an eye-catcher which for a short period of time should keep you focused. Contrast is still very important but higher brightness is permitted than in the other applications.
Too often the surrounding environmental factor is not taken into proper consideration.
The result is poor “eye-gonomics” for the viewers:
- low concentration
- eye fatigue
An “eye-gonomical” display:
- is balanced with the surrounding environment
- ensures bright and clear accessible image to the viewer
- prevents the viewer from eye fatigue and thus loss of concentration
The first general empirical rule for an “eye-gonomical” display is:
- The brightest point in a room should be no more than 10 times brighter than the darkest point in the room
This is important as the display is normally the brightest point in a room.
This is called the general room luminance ratio.
Normally the brightest and the darkest part of a room will not be in the field of vision at the same time and thus not force the eye to switch between adaption levels constantly.
The second general empirical rule for an “eye-gonomical” display is:
- The brightness of the objects that you are working with (e.g. the display and a piece of paper on the desk or a whiteboard) should have no bigger difference in brightness than a factor 3.
This is called the task luminance ratio
The eye does not switch adaption level when looking at the tasks when the difference in brightness between the tasks is kept at maximum 3 – switching adaption level = eye stress
Important factors when making an “eye-gonomical” good display:
- the brightness levels in the room and working area
- the contrast in the perceived screen image
The importance of contrast:
It is the contrast of the final image that we see on the screen that is important - NOT the contrast of the projector or the screen alone.
The perceived image contrast is a mixture of:
- Projector brightness
- Projector contrast
- Ambient light level
- Screen gain
- Screen size
- Screen’s reflectance of ambient light
We must re-calibrate our expectations to image contrast to real/realistic values.
Empirical studies show: In order for a viewer to be able to see detailed information in a clear way in an Excel spread sheet the minimum acceptable contrast in the image should be 15:1
Good contrast begins at 20:1 in image contrast ratio.
In a control room the minimum requirement is normally a 50:1 image contrast ratio.
What is the display trend?
The display of tomorrow will be an “eye-gonomical” display balanced with the surrounding environment in terms of:
- Viewing angles
- Color uniformity and vividness
- Resolution (very important in control rooms)
Visual Displays and “eye-gonomics”
We work with our partners to ensure:
Highest possible image contrast at an “eye-gonomical” brightness level
Projection display design tools
Can we predict the performance of a projected display?
Visual Displays and our partner dnp denmark have developed calculation tools which will give a quite accurate prediction of the display performance based upon input values which should be relatively easy to access before an installation is made.