Fig 1.
The three ETDRS charts.
Fig 2.
Illustration of cardinal points (red dots) where measurements were made for the tablets (left) and for the EDTRS charts (right).
Fig 3.
Luminance of black (left) and white (centre) squares, and of Michelson contrast (right) for the seven tablets at nominal maximum (“100%”, top) to minimum (“0%”, bottom) brightness settings.
Coloured surfaces in each plot also demonstrate luminance and contrast uniformity, by joining the nine measured values. Ceiling contour plots represent the mean uniformity profile of all seven tablets. Cyan surface: iPad 3 tablet. Grey surfaces: iPad 4 tablets. Blue surfaces: iPad Air 2 tablets. Data for the three EDTRS charts based on luminance of black optotypes and adjacent white backgrounds are shown in the lowermost plots (red surfaces).
Table 1.
Luminance values (cd/m2) for seven tablets at five different nominal brightness settings.
Values are the mean of the nine values measured across the screen for black and for white squares. Measurements were made with room lights off. Device/setting combinations for white squares which do not meet the BS 4274 requirement (≥ 120 cd/m2) are in bold, and those which do not meet the ICO requirement (≥ 80 cd/m2) are underlined.
Table 2.
Contrast values (%) for seven tablets at five different nominal brightness settings.
Measurements were made with room lights off. Values are the mean of the nine calculated contrasts from values measured across the screen for black and for white squares. MC: Michelson contrast. WC: Weber contrast. All tablets met the requirements of the ICO standard (Lblack/Lwhite ≤ 15%) and of BS 4274 (Weber contrast ≥ 90%).
Table 3.
Luminance (cd/m2), contrast (%) and luminance uniformity of three EDTRS charts.
Measurements were made with room lights on. Values represent the mean of the nine values measured across the chart for black optotypes and for adjacent white areas. All charts met BS 4274 (≥ 120 cd/m2) and ICO requirements (≥ 80 cd/m2) for luminance and for contrast (BS 4274, Weber contrast ≥ 90%; ICO, Lblack/Lwhite ≤ 15%). Chart parameters which do not meet the BS 4274 luminance uniformity requirements (>80%) are in bold.
Table 4.
Luminance uniformity (white squares, Lmin/Lmax, %) of seven tablets at five different nominal brightness settings.
Measurements were made with room lights off. Device/setting combinations which do not meet the BS 4274 requirements (> 80%) are in bold.
Table 5.
Pairs of data (room lights off→room lights on) for three tablets.
For luminance and contrast, values represent the mean of the nine values measured across the screen for black and for white squares at the same location, with the nominal brightness level set at “75%”. Screen parameters which do not meet the BS 4274 requirements are in bold.
Table 6.
Pairs of data (room lights off→room lights on) for EDTRS charts.
For luminance and contrast, values represent the mean of the nine values measured across the chart for black letters and for adjacent white areas. Chart parameters which do not meet the BS 4274 requirements are in bold.