Background: In in-patient care facilities, 1 in 5 medication doses is administered incorrectly. A hospital environment which supports the performance of the health-care staff will positively impact patient safety. Objectives: Determine which lighting leads to the least reading mistakes of medication labels. Design: Experimental study with repeated measures. Setting: Study was performed under controlled conditions in the Netherlands. Participants: In total the data of 37 participants are analyzed and described. Inclusion criteria were: female, aged between either 18–30 years old (M = 26.0, SD = 3.1) or between 55 and 67 years old (M = 57.9, SD = 2.7) years old, with normal vision. Eligible participants were personally invited to participate. Methods: Per participant, the readability of three different labels (Blister, Baxter and Orange) and four different font sizes (4.5 pt, 3.5 pt, 3.0 pt, and 2.5 pt Arial Capital) were assessed under nine different light conditions (three illuminances (E),100lx, 500lx, and 1000lx and three correlated color temperatures (T cp ): 3000 K, 4000 K, and 6500 K). The participants had to read out loud text sequences of 10 letters per medication label. The numbers of errors were counted and analyzed. Results: The results show a significant difference between numbers of errors related to: 1. Light condition, 2. Age, 3. Label material, 4. Font size. The impact of the light condition is not identical for the different types of label and the font sizes. The impact of the light conditions is the strongest for the smallest font size (2.5 pt) and participants with Visual Acuity < 1. Conclusion: Lighting has an impact on the number of errors. Older people make more errors than younger people. The type of label has an impact on the number of errors made. The font size has an impact on number of errors made. For font sizes <4.5 pt (Arial), reading medication labels (Blister, Baxter and Orange) under illuminance levels of 100lx, will lead to significantly more errors than E ≥ 500lx. The light condition that generates the least errors for the total test population, all font sizes, and all different materials was the one with an E of 1000lx and a T cp of 4000 K. People with an insufficient Visual Acuity (VA) benefit most from a higher illuminance level, especially for the Orange labels. When the VA is well-adjusted (sufficient to good) and the font size is as recommended for medication labels (Arial Capital ≥ 4.5 pt) the impact of the lighting on number of errors is limited for all of the age groups.