| 摘要 |
PROBLEM TO BE SOLVED: To obtain a back light unit for LCD having high front surface luminance and a wide visual field angle, by using a bead-contg. sheet and/or rugged line diffusion sheet as a diffusion sheet and using a cholesteric liquid crystal film as a polarizing plate. SOLUTION: This back light unit 1 consists of the diffusion sheet 2, the cholesteric liquid crystal film 3 and a quarter-phase plate 4. The diffusion sheet 2 consists of the bead-contg. sheet and/or the rugged line diffusion sheet. The surface luminance of the back light unit 21 is enhanced and the visual field angle is widened by using the bead-contg. sheet and/or the rugged line diffusion sheet as the diffusion sheet 2. The quarter-phase plate 4 has an effect for converting circular polarized light transmitted through the cholesteric liquid crystal film 3 to linearly polarized light. Then, the linearly polarized light necessary for the LCD is obtd. with the high luminance by arranging the quarter- phase plate 4 behind the cholesteric liquid crystal film 3. |
