This paper examines the effects of housing design upon the amount of natural light available for cuing of the human circadian system. It further assesses whether the conditions present in historic Boston row houses, when considered in the context of human moving around, can be adapted to provide sufficient light to maintain occupants' circadian rhythms. While software has been developed to simulate the amount of light in lux or lumens being received on a sensor point, these programs have generally been used to calculate the light received on a static, horizontal surface, such as a desk or other workspace. For the sake of determining a room's circadian potential, however, the sensor used must be vertical, as is the human eye during the day, and must be able to both rotate and translate – i.e. it must move forward and backward in a room and turn to face different viewpoints, as a human user does. Based on a series of simulations which take into account these factors it is possible to offer suggestions for both restoration and future design.