Design And Fabrication Of Highlighting Optical Film For Direct-Lit Backlight

Two diffuser films are usually used in direct-lit backlight unit to form a uniform illumination.To increase the brightness at the main viewing angle,two brightness enhancement films are also used.Four films make backlight unit higher cost and lower efficiency.The use of specially designed lenses array in the direct-lit backlight unit can help increase the luminance,which also has the problem of large volume.In this paper,a design method of highlighting optical film is presented.The highlighting optical film designed by this method can effectively increase the brightness of the direct-lit backlight unit and do not raise the volume of the direct-lit backlight unit.First,two-dimensional microstructure curves for uniform illumination of a single point light source are designed based on Snell's law and energy conservation law.The micro-structure curves are designed based on the ideal point light source.With the considerations that the two actual light sources(LED and Mini-LED)both have certain light-emitting size,the microstructure curves are optimized to improve the effects on uniformity.Then,according to the real arrangements of the two backlight units,the corresponding combination method is proposed.The simulations are carried out.The simulation results show that: The center brightness of the LED and Mini-LED directlit backlight are increased by 172.76% and 102.87% after the use of the highlighting optical film,respectively.The designed microstructure films are fabricated and the practical tests are carried out.The measurement results show that: the central brightness of the LED and Mini-LED direct-lit backlight with highlighting optical film are increased by 120.44% and 71.29%,respectively.The highlighting optical films designed in this paper can effectively improve the direct-lit backlight's center brightness and have not increase on its volume.