[54] SURFACE LIGHT SOURCE DEVICE
[75] Inventor: Kazuaki Yokoyama, Saitama, Japan
[73] Assignee: Enplas Corporation, Kawaguchi, Japan
[21] Appl. No.: 666,901
[22] Filed: Mar. 11,1991
[30] Foreign Application Priority Data
Jun. 19, 1990 [JP] Japan 2-63982[U]
Jun. 19, 1990 [JP] Japan 2-63983[U]
Aug. 2, 1990 [JP] Japan 2-81739[U]
[51] Int. CI.' F21V 8/00
[52] U.S. CI 362/31; 362/223
[58] Field of Search 362/26, 31, 32, 307,
362/223
[56] References Cited
U.S. PATENT DOCUMENTS
2,347,665 5/1944 Christensen et al 362/31
4,779,166 10/1988 Tanaka et al 362/31
4,811,507 3/1989 Bianghet 362/31
4,860,171 8/1989 Kojima 362/31
4,937,709 6/1990 Yanagi et al 362/31
4,965,950 10/1990 Yamada 362/31
FOREIGN PATENT DOCUMENTS
59-8809 2/1984 Japan .
61-34188 3/1986 Japan .
61-133502 6/1986 Japan .
536887 5/1941 United Kingdom 362/31
664193 1/1952 United Kingdom 362/31
Primary Examiner—-Ira S. Lazarus
Assistant Examiner—Richard R. Cole
Attorney, Agent, or Firm—Cushman, Darby & Cushman
[57] ABSTRACT
A surface light source device comprising a linear light source, a light transmitting member having an end surface of incidence located in the vicinity of the light source, a diffusing plate arranged on the front surface of the light transmitting member and a reflecting plate arranged on the rear surface of the light transmitting member; pattens formed as portions having diffusing functions being arranged on the rear surface of the light transmitting member, and the portions having the diffusing function being sparse in area in the vicinity of the center of the end surface of incidence and becoming denser as the portions are farther from the end surface of incidence. The surface light source device is adapted so as to uniformalize luminance on the diffusing plate.
7 Claims, 4 Drawing Sheets
