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Purpose: This study examined how optimal colour/illumination conditions and the efficacy of the iPad, LuxIQ and Smart Bulb varied as a function of print size in younger, older and visually impaired adults.

Methods: Participants with visual impairments and simulated low vision (SLV) read the MNRead using the iPad, LuxIQ and Smart Bulb.

Results: In the impairment condition at 1.20 logMAR, the iPad (M = 9.49, 95% CI [3.18, 19.42]) and LuxIQ (M = 15.95, 95% CI [9.54, 24.86]) improved the reading speeds. At 0.80 logMAR (SLV), all devices improved reading speeds of older adults (iPad (M = 28.70, 95% CI [14.65, 42.51]); LuxIQ (M = 49.63, 95% CI [30.04, 69.68]); Smart Bulb (M = 23.11, 95% CI [3.33, 42.11])), but in younger adults only the LuxIQ (M = 13.04, 95% CI [3.21, 21.27]) did so. In the impairment condition, the iPad (M = 5.54, 95% CI [0.31, 12.13]) and LuxIQ (M = 13.90, 95% CI [7.88, 23.49]) improved reading speeds. In the SLV condition, age was a significant predictor of reading speed at 1.20 logMAR (F_3,164 = 10.74, p < 0.001, Adj. R² = 0.16). At 0.80 logMAR, age and luminance, but not colour, were significant predictors (F_3,164 = 52.52, p < 0.001, Adj. R² = 0.49). In the impairment condition, both age and lux were significant predictors of reading speed at 1.20 (F_3,85 = 7.14, p < 0.001, Adj. R² = 0.20) and 0.80 logMAR (F_3,85 = 7.97, p < 0.001, Adj. R² = 0.22), but colour was not.

Conclusions: Light source effectiveness and optimal colour/illumination vary as a function of print size. It appears that print size is the most important factor for improving reading speed. As print size decreases, luminance becomes crucial, and only at the smallest print sizes does the effect of colour become useful.