To enhance the efficiency of the cooling structure of a surface light source device used in a back light or the like of a transmission type display panel and prevent the sticking of dust.
A device 0 has a housing 1, a diffusion plate 2, a reflecting plate 3, a lamp 4, and an electric circuit part 5. The housing 1 has a window part positioned in the front, a bottom part 6 positioned in the rear, and a side part 7 which connects both parts to form a flat space. The diffusion plate 2 is fixed to the window part of the housing 1. The reflecting plate 3 is supported by the side part 7, placed in the flat space, and partitions the flat space into a sealed space 8 in the front and an open space 9 in the rear. The lamp 4 is housed in the sealed space 8 positioned just over the reflecting plate 3 but just under the diffusion plate 2 to radiate light to the diffusion plate 2. The electric circuit part 5 is housed in the open space 9, electrically connected to the lamp 4 to light the lamp 4. Openings 7a, 7b are formed in the side part 7 of the housing 1, introduce cooling wind supplied from the outside into the open space 9 to radiate heat accumulated inside the housing 1.
YONEYA MASARU
OMORI TAKAYOSHI
SUZUKI TERUHIRO
