The search for efficient, auto-sustainable constructions that allows the user a contact with the outer environment has stimulated the development of advanced strategies, in various devices, for the exploitation of the daylight. A low cost data acquisition system was developed in this study, to observe the distribution of the natural light inside a prototype and to evaluate the quantitative performance for redirecting systems. The luminous sensor is a light dependent resistor, that responds to the illuminance with a reduction in the resistance when illuminated, through a log-log dependence. Calibration curves are set up to relate the change of resistance to absolute illuminance. It therefore provides a continuous investigation of the illuminance for various sampled points in the interior test space with a 0.03% digital error due to the 12-bit resolution. The final measured error of 5% is mainly due to the system calibration and resistance memory history. The circuit connects to a standard parallel port of any Personal Computer and supplies 64 analog inputs, one for each luminous sensor. The circuit can be easily modified to attend different quantities of analog inputs or communication ports. (c) 2007 Elsevier Ltd. All rights reserved.