(12) UIllt€d St3t€S Patent (10) Patent No.: US 6,476,552 B1 Yoneda (45) Date of Patent: Nov. 5, 2002 (54) ELECTROLUMINESCENT LAMP Primary Examiner—Nimeshkumar D. Patel __ _ Assistant Examiner—Thelma Sheree Clove (75) Inventor? K911 Yoneda> Ionlkawa (JP) (74) Attorney, Agent, or Firm—Schulte Roth & Zabel LLP; J lE.Ltk;D L.An tt' (73) Assignee: Seiko Precision, Inc (JP) O6 u Z er Onna go 1 (57) ABSTRACT ( * ) Notice: Subject to any disclaimer, the term of this _ _ _ patent is extended or adjusted under 35 The difference of luminance between a front surface side and U.S.C. 154(b) by 0 days. a rear surface side as viewed from the front surface side is reduced in a multi-layered EL lamp. An EL lamp includes a (21) App1_ No_; 09/548,874 first laminate formed by serially laminating a first transpar_ _ ent electrode, a first luminescent layer and a first insulating (22) Bled‘ Apr‘ 13’ 2000 layer, a second laminate formed by serially laminating a (39) Foreign Appiioation Priority Data second transparent electrode, a second luminescent layer and a second insulating layer on the first laminate, and a rear Apr. 14, 1999 (JP) ......................................... .. 11-107164
electrode formed on the second laminate, wherein a dielectric constant between the first and second transparent electrodes is set to a value smaller than a dielectric constant between the second transparent electrode and the rear electrode. This can be achieved by limiting the amount of a high dielectric material to be mixed in the first insulating layer to not greater than 90% in terms of a weight ratio of a high dielectric material mixed in the second insulating layer, or by increasing the thickness of the first luminescent layer to 130 to 250% of the thickness of the second luminescent layer. After the adjustment is made in this way, the thickness of the first insulating layer may be set to not greater than 90% of the thickness of the second insulating layer or may be omitted.
13 Claims, 4 Drawing Sheets