In order to make the brightness approximately uniform over a diffusion board, a back-light device is provided with a light transmission controlling film having a planar form in a shape of a projection of the lamp on the diffusion board. The film is disposed in parallel to the lamp axis between the lamp...http://www.google.com.au/patents/US4916580?utm_source=gb-gplus-sharePatent US4916580 - Back-light device
