1. TFT-LCD and Visual Performance 2006-03-04 이현철

2. Nuclear I&C and Information Engineering Laboratory 2006.03.042 Preface  From the previous seminar, it was told that lighting in the workplace may influence the performance of people by way of several mechanisms  This presentation deals with visual performance related to TFT- LCD, the most popular VDT for computers today. Contrast ratio and text colors are factors that are likely to affect VDT performance.

3. Nuclear I&C and Information Engineering Laboratory 2006.03.043 Contents  Effects of the followings on visual performance with TFT-LCD 1. Contrast ratio 2. Text color  References Chin-Chiuan Lin, Effects of screen luminance combination and text color on visual performance with TFT-LCD, IJIE, Vol.35(2005), 229-235 Chin-Chiuan Lin, Effects of contrast ratio and text color on visual performance with TFT-LCD, IJIE, Vol.31(2003), 65-72

4. Nuclear I&C and Information Engineering Laboratory 2006.03.044 Previous studies and research need  Previous studies on contrast ratio with CRT display McLean (1965) indicated that the contrast ratio had significant effect on legibility. Legibility was found to increase as contrast ratio value increased. Shieh and Lin (2000) found that contrast ratio might play a more important role on visual performance than chromaticity contrast. Wang and Chen (2000) found that contrast ratio significantly affected visual performance. Visual acuity increased as contrast ratio increased up to 8:1 and then decreased once the contrast ratio was greater than 8:1.  Because the optical characteristics of CRT and TFT-LCD are different (MacKenzie and Riddersma, 1994; Post and Reinhart, 1997; Stix, 1989), the effect of contrast ratio on visual performance for CRT may not apply to TFT- LCD. Thus, there is a need to evaluate the effects of contrast ratio and text color on visual performance using TFT-LCD.  Several human factors experiments were carried out to investigate the effects.

5. Nuclear I&C and Information Engineering Laboratory 2006.03.045 Human Factors Experiment 1  Experiment 1 Independent Variables Seven levels of text color red, green, blue, yellow, purple, cyan, and gray Two levels of contrast ratio C6 (90 cd/m 2, 15 cd/m 2 ) C3L (45 cd/m 2,15 cd/m 2 ) Contrast ratio and text color were all served as within-subjects factors. Task a stimulus composed of four capital English letters was presented in the central area of the screen for 200 ms (approximately one eye-fixation duration). The four letters was presented at the corners of an area which was approximately 2 cm×2 cm. The height for the 12-point letters was 3.36 mm. The subtended visual angle of the letters was 23 min of arc. The subjects were required to write down as many letters as they could identify. Dependant Variable Visual performance was defined as the percentage of correctly identified letters.

6. Nuclear I&C and Information Engineering Laboratory 2006.03.046 Experiment set-up The ambient illumination was produced by fluorescent lamps and was about 450 lx. No glare appeared on the TFT-LCD screen.

7. Nuclear I&C and Information Engineering Laboratory 2006.03.047 Human Factors Experiment 1 (Cont.)  Experiment 1 Results The results of analysis of the variance indicated that contrast ratio had a significant effect on percentage correct (F(1,252)=8.09, p<0.01). The percentage correct for contrast ratio C6 was significantly greater than that for C3L. Text color did not significantly affect visual performance.

8. Nuclear I&C and Information Engineering Laboratory 2006.03.048 Human Factors Experiment 2  Experiment 2 Independent Variables Six levels of text color red, green, yellow, purple, cyan, and gray Four levels of contrast ratio C6 (90 cd/m 2, 15 cd/m 2 ) C3H (90 cd/m 2, 30 cd/m 2 ) C3L (45 cd/m 2, 15 cd/m 2 ) C1.5 (45 cd/m 2, 30 cd/m 2 ) The experimental apparatus, workplace conditions, task, and procedure were the same as those used in Experiment 1 Every subject completed the 24 combinations (4 contrast ratio×6 text color) of the within-subject factors.

9. Nuclear I&C and Information Engineering Laboratory 2006.03.049 Human Factors Experiment 2 (Cont.)  Experiment 2 Results The results of analysis of the variance indicated that contrast ratio had a significant effect on percentage correct (F(3,432)=10.88, p<0.01). The percentage of correctly identified letters was greatest for C6, followed by C3H, C3L, and C1.5. Text color did not significantly affect visual performance.

10. Nuclear I&C and Information Engineering Laboratory 2006.03.0410 Human Factors Experiment 3  Experiment 3 Independent Variables Three levels of text color yellow, purple, and cyan Six levels of contrast ratio C6 (90 cd/m 2, 15 cd/m 2 ) C3H (90 cd/m 2, 30 cd/m 2 ) C3L (45 cd/m 2, 15 cd/m 2 ) C2 (90 cd/m 2, 45 cd/m 2 ) C1.5 (45 cd/m 2, 30 cd/m 2 ) C1 (45 cd/m 2, 45 cd/m 2 ) The experimental apparatus, workplace conditions, task, and procedure were the same as those used in Experiment 1 Every subject completed the 18 combinations (6 contrast ratio×3 text color) of the within-subject factors.

11. Nuclear I&C and Information Engineering Laboratory 2006.03.0411 Human Factors Experiment 3 (Cont.)  Experiment 3 Results The results of analysis of the variance indicated that contrast ratio had a significant effect on percentage correct (F(5,324)=80.63, p<0.01). The percentage of correctly identified letters was greatest for C6, followed by C3H, C2, C3L, C1.5, and C1. Text color also significantly affected percentage of correctly identified letters (F(2,324)=12.3, p<0.01). The visual performance was greatest for purple, followed by cyan, and yellow. The contrast ratio×text color interaction was statistically significant (F(10,324)=7.7, p<0.01). Right-side figure shows the contrast ratio×text color interaction. The visual performance significantly decreased when contrast ratio was less than C2. When contrast ratio was greater than C2 the difference of visual performance among colors was not significant.

12. Nuclear I&C and Information Engineering Laboratory 2006.03.0412 Human Factors Experiment 4  Experiment 4 Independent Variables Seven levels of text color red, green, blue, yellow, purple, cyan, and gray Six levels of contrast ratio C16 (80 cd/m 2, 5 cd/m 2 ) C8H (80 cd/m 2, 10 cd/m 2 ) C8L (40 cd/m 2, 5 cd/m 2 ) C4H (40 cd/m 2, 10 cd/m 2 ) C4L (20 cd/m 2, 5 cd/m 2 ) C2 (20 cd/m 2, 10 cd/m 2 ). The experimental apparatus, workplace conditions, task, and procedure were the same as those used in Experiment 1 Eight subjects were randomly assigned to each of the seven levels of the between- subjects factor, text color. Every subject completed the six treatments of screen luminance combination (2 text luminance×3 background luminance) of the within- subjects factor.

13. Nuclear I&C and Information Engineering Laboratory 2006.03.0413 Human Factors Experiment 4 (Cont.)  Experiment 4 Results The results of analysis of variance indicated that screen luminance combination (F(5, 245)=7.41, p<0.01) had significant effect on visual performance. The screen luminance combination C16 resulted in best visual performance, followed by C8L, C4H, C8H, C4L, and C2. Text color did not significantly affect visual performance. Subjects also showed somewhat greater grand-mean visual preference for chromatic text than for achromatic text, but the difference did not reach statistical significance. SourceDFSSMSF-value p a Between-subject factor Text color (Tc)60.26040.04340.57NS Error493.73280.0762 Within-subject factor Screen luminance combination (Sc) 50.09610.01927.410.001 Tc×Sc Tc×Sc300.06270.00210.81NS Error2450.63530.0026 a p<0.05 significant level. Independent variables nMean (SD) Screen luminance combination C25663.15 (11.48) C4L5666.15 (12.06) C4H5667.46 (11.48) C8L5667.83 (11.37) C8H5666.41 (13.22) C165668.26 (11.83) Text color Blue4870.43 (11.27) Cyan4868.89 (11.03) Yellow4868.39 (10.57) Red4867.50 (11.82) Purple4864.30 (10.82) Green4863.94 (11.70) Gray4862.36 (11.46)

14. Nuclear I&C and Information Engineering Laboratory 2006.03.0414 Data Compile (Exp3 & Exp4) In general, Increase in contrast ratio resulted in better visual performance There is one exceptional area including C8H(80/10), C4H(40/10).

15. Nuclear I&C and Information Engineering Laboratory 2006.03.0415 Conclusion  Better visual identification performance was obtained for higher contrast ratio than for lower contrast ratio. Visual performance improved as the contrast ratio increased.  According to the results, higher screen luminance combination would be better on low contrast ratio and lower screen luminance combination would be better on high contrast ratio for TFT-LCD work.  Contrast ratio played more important role on visual performance than text color for TFT-LCD screen. Text color did not affected visual performance if an acceptable level of contrast ratio was present. Text color did not differ with respect to visual performance. However, chromatic text may be more appropriate than achromatic text for TFT-LCD.

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