1. **"Readability of text presented on computer screens (e.g. on websites) is better when the overall display luminance level is high, as in positive polarity displays (dark letters on light background)."** **Per Buchner A et.al.** in [2009](http://www.ncbi.nlm.nih.gov/pubmed/19562598), display polarity per se does not affect readability. Contrast polarity is one aspect of reading that has been studied in [detail](http://legge.psych.umn.edu/pdf/read5.pdf) for visual acuity which relates to clarity of vision. It designates whether text is presented as black letters on a white background or vice versa. 2. **"Typically higher luminance of positive polarity displays leads to an improved perception of detail" per Piepenbrock C et.al.** in [2014](http://www.ncbi.nlm.nih.gov/pubmed/25141597), > Dark characters on light background (positive polarity) lead to better legibility than do light characters on dark background (negative polarity), presumably due to the typically higher display luminance of positive polarity presentations. The implications seem important for the design of text on such displays as those of computers, automotive control and entertainment systems, and smartphones that are increasingly used for the consumption of text-based media and communication. The sizes of these displays are limited, and it is tempting to use small font sizes to convey as much information as possible. Especially with small font sizes, negative polarity displays should be avoided. 3. **"Background color did not significantly affect visual acuity when studying the effects of color combination on the visual acuity and display quality using TFT-LCD. The results also indicated that chromatic background may be more appropriate than achromatic background (gray) for TFT-LCD work"** per Chin-Chiuan Lin et.al in [2006](http://www.researchgate.net/publication/228340041_Effects_of_color_combination_on_visual_acuity_and_display_quality_with_TFT-LCD). However, these results are contradictory to the findings that chromaticity contrast has a profound effect on visual performance, but matched with previous findings that chromaticity contrast cannot improve the legibility. Per the researchers, further investigation is required in the interaction effects between contrast ratio and screen luminance combinations on visual acuity and display quality with TFT-LCD. > Further, in visual performance test (psychology measure), the objective and subjective measures were often consistent in the prolonged test, such as reading and proof-reading tasks; and were often inconsistent in the short term test, such as identification and legibility tasks. It’s very difficult to explain why the inconsistency of subjective and objective results. One possible reason is the visual fatigue. In prolonged test, subjects might produce visual fatigue. > Background color also did not affect the visual acuity. The effects of background color on visual evaluation might depend on the type of measure. Contrarily, background color did have a significant effect on subjective rating. The subjective ratings on background with blue, cyan, green and purple color were significantly greater than that with red. Further, we conclude that subjects may favor cool colors than warm colors as for background color. 4. "In general, **the plain backgrounds led to faster search times than did the medium-textured backgrounds**, and blue backgrounds led to slower and more variable search times than the grey or yellow backgrounds" per Alyson L. Hill et.al. in [1999](http://www.laurenscharff.com/research/Oxford.html) > The interactions indicate that one can not make simple predictions regarding factors which lead to efficient processing. Further, search times did not correlate with participants' preference ratings of the different stimulus combinations. Designers should keep this in mind when designing software and web pages. 5. **"Search times indicate that these background variations only affect readability when the text contrast is low, and that spatial frequency content affects readability"** per Lauren F. V. Scharff et.al in [2000](https://www.osapublishing.org/oe/abstract.cfm?uri=oe-6-4-81) who has published several papers on readability of text [displays](http://www.laurenscharff.com/research/text_display_lvs.html). 6. **"Performance was significantly worse for the low text contrast, the additive combination rule, and the "culture" pattern and both patterns were worse than the uniform background"** per Lauren F. V. Scharff et.al in [2001](http://www.laurenscharff.com/research/transtext.html). Per David L. Post's Color in Electronic [Displays](http://link.springer.com/book/10.1007/978-1-4757-9754-1), "visual acuity was not substantially affected by chromaticity, when given adequate contrast, photopic viewing conditions and reasonable symbol sizes. Conversely, acuity is not affected much by luminance contrast, given adequate chromatic contrast." **For low vision observers** Many low-vision observers prefer white-on-black text per Sloan [1977](http://legge.psych.umn.edu/pdf/read1.pdf). Legge et al. in [1985](http://legge.psych.umn.edu/pdf/read6.pdf) demonstrated that **low-vision subjects with cloudy ocular media read faster with white-on-black text.** This effect is probably due to abnormal light scatter in the eye. **Upper-case is more legible than the other case styles, especially for visually-impaired readers**, because smaller letter sizes can be used than with the other case styles, with no diminution of [legibility](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2016788/) and two other studies by Martha Ziefle suggest that one of the main contributors to slower reading performance, at least after 30 minutes, could be the resolution of the characters being [read](http://www.humanfactors.com/newsletters/screen_resolution_2000.asp). **For normal vision observers** "Unfortunately, word readability is not necessarily simply related to letter identifiability and simple contrast [measures](http://vision.arc.nasa.gov/personnel/al/papers/03ei/03ei5007-46.pdf)". There has been several reported small advantages in normal reading performance for black-on-white text, especially for small letters. However, Legge et al. in [1986](http://eye.psych.umn.edu/groups/gellab/Publications_main/read8.pdf) found **no systematic effect of contrast polarity in their study of the reading performance of subjects with normal vision since reading rates showed no effect of chromaticity at any of the character sizes studied.** This experiment measured reading rates for monochrome text on CRT using a black background and either red, blue, green or white raster scan characters. Normal subjects usually read static text more rapidly. The reverse was true for low-vision subjects; their reading rates for drifting text were slightly higher (average 15%) than for static text. Most people with low vision are handicapped in reading and for many people, reading difficulty is the most serious consequence of eye [disease](http://legge.psych.umn.edu/pdf/read2.pdf). Per Shen Y et.al. in [2014](http://www.ncbi.nlm.nih.gov/pubmed/24890155), varying background luminance to maintain screen background luminance ratio is beneficial to human visual comfort.