Reflections on a VDT screen which interfere with reading the screen are
called "veiling" reflections. They may cause eye strain and tiredness.
Or they may cause one to misread the display. Both of these result in a
drop in productivity and/or quality.
These reflections are caused by relatively bright surfaces or lights which
are reflected by the face of a VDT. Bright surfaces are those which have
a much greater light intensity than the area surrounding them.
There are a number of ways to eliminate veiling reflections or to reduce
their effects. Some are measures which an individual can take without effecting
his/her neighbors. Others require changes to the building or changes which
Adjust the VDT: Try to adjust the VDT so that the reflections
disappear. This will be easier if the terminal has a tilt swivel base. Its
just like adjusting a mirror so there are no bright lights or objects in
Move the VDT: Check to see if there is another location for the
VDT within the workstation. Is there a spot to place the VDT so that there
would be no bright lights or surfaces behind the user if he/she were seated
at the VDT? Check this by placing a mirror or piece of reflective material
where the face of the screen would be located. If a better location is available,
consider whether the new arrangement of the work area will be satisfactory
and check to see if cables will reach and power is accessible from the new
Light Source: If the obscuring reflection is a light source which
can be eliminated without disturbing others, then turn it off. For example,
the light might be a task or under shelf light in the user's own work area.
Windows: If the light source is daylight from a window, close
the window blinds or drapes. In general, VDT's should be placed at right
angles to exterior windows. If the screen faces a window, there will be
reflections on the screen from the exterior. If the user faces the window,
there will be disturbing glare due to the brightness surrounding the VDT.
User reflection: Light clothes, a very dark background or a lighting
level which is too bright may cause the user to be reflected in the screen.
To get rid of the reflection, it will be necessary to eliminate the contrast
between light and dark. That is, have the user try wearing darker clothes,
reduce the intensity of the light shining on the worker or lighten the background.
Display type: If the VDT has reverse video (i.e. it can be switched
to a light background with dark images), try this. Veiling reflections are
primarily a problem when the display background is dark. With a light screen
the reflections are usually less bright than the screen and are therefore
Screen shape: Purchase VDT's with flat screens. These will reflect
objects over a narrower area than a spherical (worst) or cylindrical shaped
Reduce light level: Another strategy to minimize veiling reflections
due to light objects within a dark setting is to reduce the average lighting
level. This reduces contrast ñ and consequently veiling reflections.
In an area where the primary tasks are performed at VDT's, the lighting
level can be reduced below 40 foot candles. Where it is not necessary to
refer to documents or where task lighting is provided, the lighting level
can be reduced to as low as 20 foot candles. Satisfactory implementation
will depend on selection and arrangement of appropriate light fixtures.
Often veiling reflections are caused by bright lights in the ceiling.
There are several strategies to avoid this source of reflections.
Low brightness fixtures: The more common strategy is to install low
brightness fixtures. These are normally fluorescent fixtures with deep cell
parabolic lenses. A two foot by four foot fixture has a lens with either
18 or 24 cells. The cells are several inches deep and have parabolic sides
which give a broad distribution of light. These are much more efficient
than those with acrylic lens. The fixtures usually need only three 40 watt
(or 32 watt) fluorescent tubes to produce the light which is available from
four 40 watt tubes in an older fixture.
Do not confuse these with fluorescent fixtures having 1/2 or 1 inch square
parabolic lenses. These are low brightness fixtures but concentrate the
light over a small area so that the lighting level is uneven in the space.
These lenses are often used because they can replace the 1/8" thick
acrylic lens in an existing fixture. However, we do not generally recommend
Indirect lighting or up-lighting: This solution uses ceiling hung
fixtures that direct the light up where it is reflected off the ceiling.
Glare and shadows are nearly eliminated. This character of the lighting
has been compared to that experienced on a cloudy day. When used with task
lights which can be controlled by the user, it is considered by many to
There are several drawbacks. One is that it requires a higher than normal
ceiling. We do not recommend its use with a ceiling height lower than 10
feet. This is not available in a typical rental office building. Higher
ceilings increase building cubage, and consequently increase initial cost
and operating expenses. Indirect lighting draws attention to the ceiling.
Therefore, it requires a high quality ceiling system and installation ñ
further increasing initial costs. A 2' x 4' lay-in acoustical ceiling will
definitely have an unacceptable appearance. Another drawback is that the
same light level requires more total power than is needed with low brightness
fixture. We used this approach successfully in the SafeCard