301
g = 65°
15°
g = 0°
VDU-Friendly Lighting
VDU (visual display unit) workstations form the basis of a suitable
working environment in administrative, service, sales or technical areas.
VDUs as means of working and communicating will continue to gain
increasing importance. To enable concentrated working at a VDU, the
visual environment must not have a disruptive efect when recognising
objects on the screen. To be able to guarantee this, the illumination of
a VDU workstation must meet particular requirements.
Aspects of Light Planning
A further criterion for assessing glare is the UGR (unifed glare rating)
procedure. This procedure was developed by the International
Commission on Illumination (CIE) with the aim of standardising the
glare assessment systems in Europe. In contrast to the limit curve
procedure according to Sollner (Sollner curve), which only estimates
the glare of individual luminaires, the glare assessment according to
UGR, mostly in table form, also takes into account the arrangement of
the luminaires in the room, the luminance of the luminaires as well as
the background luminance (ceiling, walls, foor) and thus the glare of
the whole lighting installation. In this situation the lower the UGR value
is, the smaller also is the probability of glare, although the UGR value
rises with increasing room size. The UGR value thus obtained is then
fnally compared with the so-called glare indices (GI), which show the
maximum UGR limits. For ofce spaces, for example,
a maximum GI of 19 is recommended.
VDU-Friendly Lighting
A particularly important quality feature in the lighting of VDU
workstations is the avoidance of
a) direct glare from luminaires and
b) refective glare
from shiny surfaces (VDUs) at the workstation. The defnitive factor
in perceived glare is luminance in the γ > 65° range. From this angle
upwards the light will strike our eyes directly or via directly refective
surfaces. That is why particular limits apply here for the luminance
given of by luminaires. DIN EN 12464-1 describes the requirements a
VDU workstation must meet. It contains stipulations on the luminance
limits for luminaires that might be refected in VDUs. For VDU
workstations with “high state” monitor luminance > 200 cd/m2,
DIN EN 12464-1 prescribes a limit of 3000 cd/m2 in the γ > 65° range.
For VDU workstations with “high state” monitor luminance
< 200 cd/m2, DIN EN 12464-1 prescribes a limit of 1500 cd/m2 in the
γ > 65° range. The standard luminance of fat screens is currently 250
cd/m2. The user thus has the possibility of planning according to the
current state of technology.
Psychological Glare
Each person reacts diferently to the stimulae in the environment
around them. Sensitivity to the luminance present in a person’s
feld of vision and the resulting evaluation is always subjective. For
good results the selection of the luminaires taking into account their
photometric properties and above all the correct arrangement of the
luminaires in the room is crucial.
At VDU workstations furthermore the inclination of the screen has
an exceedingly signifcant infuence on the occurrence of refections.
It should accord with the main line of sight, but can be individually
adjusted depending on personal habits or the position of the screen.
For further information see BGI 856 “Illumination in ofces”. This
recommends a screen inclination of 15° for VDU workstations.
