Author:

Abstract:

Holographic diffusers are relatively new to the lighting industry. Because of their high transmittance (often >90%, where classic diffusers have a transmittance of the order of 50% ) they allow for the optical design of efficient luminaires. However, holographic diffusers are designed for coherent light that is incident parallel to the normal of the material surface. For lighting applications incoherent light that is incident at all angles between normal and grazing incidence have to be considered. In this work the optical scattering by a holographic diffuser is studied experimentally. The Bidirectional Scatter Distribution Function (BSDF) is measured, both in transmission and reflection geometry, with an in house designed and constructed experimental setup [1]. The measured data are then deconvolved with the instrument function of the experimental set up to take into account the effects of beam dimensions and detector diameter [2]. It is found that beam spread angle and total transmittance and reflectance vary strongly as a function of angle of incidence. The data provided by the manufacturer of the diffuser are only valid for normal incidence. This has to be taken into account in the optical design of luminaires incorporating holographic diffusers.