Design method for a thin uniform direct backlight using a diffuser plate with a pattern on the surface and optical films

Abstract

We researched a design method for improving uniformity of a thin direct backlight by using a diffuser plate with a pattern on the surface. It was found that the transmittance angle distribution (TAD) of the diffuser plate indicated the performance for uniformity and was an essential physical quantity for a backlight optical system with the diffuser plate. We clarified the relationship between the design parameters of the diffuser plate (the pattern and the mean free path of a ray in the diffuser plate) and the TAD of the diffuser plate by a simulation based on Mie theory and the experiments. The direct backlight, in which the distance between the diffuser plate and the lamps was less than 5 mm, was demonstrated. The illuminance uniformity of the diffuser plate was improved to 0.98 by the diffuser plate with a pattern that makes the TAD nearly constant distribution. Furthermore, the optical films on the diffuser plate were optimized, and the illuminance uniformity of the backlight achieved 0.99.