**3.7 Effect of contrast ratio**

The result on the effect of contrast ratio to visual symptoms is described in Table 7. There are three kind of contrast ratio investigated. They are -50.83%, +24.58% and 0%. The ratio can vary from 100% (positive) to zero for targets darker than the background, and from zero to minus infinity (-∞) for targets brighter than the background (Grether and Baker, 1972). Statistical binomial test at 5% significant level shows that all contrast ratios causes eyestrain symptoms (75% of users). Blurred vision and dry and irritated eyes symptoms were experienced by 63% and 50% of users at contrast ratios of --50.83% and 0% (or -0.56%) respectively.


*p*> 0.05 ; N = 8

Table 7. Result of Experiment and Binomial Test of Visual Symptoms of Contrast Ratio
