Research has shown that increased blue light exposure from higher correlated color temperature (“CCT”) light sources can lead to improvement in adults’ cognitive performance. No such data has been available for preschoolers, when attention and executive function skills are developing. This study of 38 children (ages 4.5 – 5.5) addressed that knowledge gap. Compared to children in the control group, children who were exposed to higher-CCT light showed similarly minor improvement in sustained attention, but more than twice the increase in their accuracy (15.2% vs. 6.5%) when switching between tasks (cognitive flexibility). This demonstrates that the relationship between the lighting environment and cognitive performance emerges early in development. It also highlights the need for further research on how blue light exposure impacts children’s cognitive development, sleep, circadian timing, and melatonin production.