Two experiments were conducted in this study. The first
experimentinvestigated the effects of screen text/background
color combination, work-break schedule, and workpace on visual
performance, visual fatigueand viewing distance during VDT work.
Visual performance was measured by correct percentage of
targets found, and visual fatigue was measured by the change of
critical fusion frequency (CFF) and subjective visualstrain.
The results showed that screen color combination significantly
affected performance. The subjects'' performance for red text
on greenbackground was significantly poorer than for white-on-
black, white-on-blue, yellow-on-blue, and black-on-white.
Performance for thescreen color combinations was
significantly correlated with color difference. Workpace
also affected performance. Subjects had betterperformance
under slow workpace. Work-break schedule had no
significanteffect on performance. CFF change was not
significantly affected by screen color combination, work-
break schedule, or workpace, though significant CFF
reduction was found during VDT work. Neither
colorcombination nor other independent variables had
significant effects onsubjective visual strain. Screen color
combination significantly affected viewing distance, with red-
on-green resulting in the shortestviewing distance. Viewing
distance for the other four combinations didnot differ
significantly. Work-break schedule also affected viewing
distance. Subjects with a 5-min break for every 25 min of
work hadgreater viewing distances than subjects with a 10-min
break for every 50min of work. Workpace had no significant
effect on viewing distance. Subjective visual strain was
significantly related to viewing distance. Subjects with a
longer viewing distance generally experienced less
subjective visual strain. It is suggested by the results of
this studythat color combination with greater color difference
be preferred in VDTscreen design. In addition, a work schedule
with frequent, short breaks may be employed to reduce VDT work
problems. The second experiment investigated the effects of
screen color combination, typeface, ambient illumination, and
duration of stimulus onrecognition of characters briefly
presented on VDT. Results showed thatcolor combination and
ambient illumination had no significant effects onvisual
performance. The results might arise from some characteristics
ofthe experiment. Longer duration of stimulus resulted
in betterperformance as expected. But interactions involving
duration of stimuluswere not significant. Typeface
significantly affected performance.Subjects performed better
for standard Computer type. Aestheticallypleasing Kai type
might be detrimental to performance. Subjects alsoshowed
differential preference for color combinations. Red-on-green was
ranked inferior to color contrasts generally used in computer
software.