We assess the influence of hourly variation in sunlight on the productivity of New York City cab drivers. The cab-driver-ride sample examined here has a lower “assortative match” between tasks and employee experience and abilities, and quasi-random matching between cab riders and cab drivers significantly lowers unobserved selection based on customer needs and driver ability. We draw on a sample of 9.76 million cab-driver-rides. With increasing hourly sunlight, cab drivers take longer to complete rides. In terms of relative effect sizes, after driver experience and day of the week, solar radiation (i.e., sunlight) is the third-most important influence on productivity. The effect sizes are small but meaningful--36.76 min of lost time for a 100% increase in lux (ranging from <200 lx, which represents light during the thickest possible storm clouds at midday to 20,000 lx, which represents the light present in an entirely clear blue sky at midday).