Daylight impact on energy performance of internal lighting

Daylight in interior offers a considerable contribute of energy allowing to reduce the level of electric lighting. The key to design an integrated lighting system is the electric lighting control strategy. An optimal lighting system has to consider the different presence of daylight in the zones to arrange the most favorable luminaires layout. An automatic control system could be employed to switch or dim selected groups of luminaires. The paper suggests a criterion to evaluate the yearly daylight impact on energy performance of internal lighting according to daylight availability, the lighting system layout and the control system arranged. The evaluation is useful for designers to estimate the operation costs in reference to the initial costs.