Illumination method and light-emitting device

• US 9,818,914 B2
• Filed: 09/15/2016
• Issued: 11/14/2017
• Est. Priority Date: 09/02/2011
• Status: Active Grant

• Current Assignee: Citizen Electronics Company Limited
• Original Assignee: Citizen Electronics Company Limited
• Inventors: Horie, Hideyoshi
• Primary Examiner(s): Lee, Kyoung
• Assistant Examiner(s): Mehta, Ratisha
• Application Number:
  US15/266,377
• Publication Number:
  US 20170005237A1
• Time in Patent Office: 425 Days
• CPC Class Codes: F21K 9/233 specially adapted for generating a spot light distribution, e.g. for substitution of reflector lamps
• CPC Class Codes: F21Y 2115/10 Light-emitting diodes [LED]
• CPC Class Codes: H01L 27/156 two-dimensional arrays
• CPC Class Codes: H01L 33/06 within the light emitting region, e.g. quantum confinement structure or tunnel barrier
• CPC Class Codes: H01L 33/28 containing only elements of Group II and Group VI of the Periodic Table
• CPC Class Codes: H01L 33/32 containing nitrogen
• CPC Class Codes: H01L 33/50 Wavelength conversion elements
• CPC Class Codes: H01L 33/502 Wavelength conversion materials
• CPC Class Codes: H01L 33/504 Elements with two or more wavelength conversion materials
• CPC Class Codes: H05B 33/02 Details
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/22 using optical feedback

Abstract

To provide an illumination method and a light-emitting device which are capable of achieving, under an indoor illumination environment where illuminance is around 5000 lx or lower when performing detailed work and generally around 1500 lx or lower, a color appearance or an object appearance as perceived by a person, will be as natural, vivid, highly visible, and comfortable as though perceived outdoors in a high-illuminance environment, regardless of scores of various color rendition metric. Light emitted from the light-emitting device illuminates an object such that light measured at a position of the object satisfies specific requirements. A feature of the light-emitting device is that light emitted by the light-emitting device in a main radiant direction satisfies specific requirements.

Claims

1. A light-emitting device incorporating a bluish purple or blue light-emitting element, wherein

light emitted from the light-emitting device includes, in a main radiant direction thereof, light whose distance D_uvSSL from a black-body radiation locus as defined by ANSI C78.377 satisfies −

0.0325≦

D_uvSSL<

0, and

(1) if an a* value and a b* value in CIE 1976 L*a*b* color space of 15 Munsell renotation color samples from #01 to #15 listed below when mathematically assuming illumination by the light emitted from the light-emitting device in the radiant direction are respectively denoted by a*_nSSL and b*_nSSL (where n is a natural number from 1 to

     15), and

an a* value and a b* value in CIE 1976 L*a*b* color space of the 15 Munsell renotation color samples when mathematically assuming illumination by a reference light that is selected according to a correlated color temperature T_SSL (K) of the light emitted from the light-emitting device in the radiant direction are respectively denoted by a*_nref and b*_nref (where n is a natural number from 1 to

     15), then each saturation difference Δ

C_n satisfies

−

2.7≦

Δ

C_n≦

18.6 (where n is a natural number from 1 to

     15),

where Δ

C_n =√

{(a*_nSSL)² +(b*_nSS)²}−

√

{(a*_nref)² +(b*_nref)²}

with the 15 Munsell renotation color samples being;

#01 7.5P 4/10

#02 10PB 4/10

#03 5PB 4/12

#04 7.5B 5/10

#05 10BG 6/8

#06 2.5BG 6/10

#07 2.5G 6/12

#08 7.5GY 7/10

#09 2.5GY 8/10

#10 5Y 8.5/12

#11 10YR 7/12

#12 5YR 7/12

#13 10R 6/112

#14 5R 4/14

#15 7.5RP 4/12.

2. The light-emitting device according to claim 1, wherein an average saturation difference represented by formula (3) below satisfies formula (4) below;

3. The light-emitting device according to claim 1, wherein if a maximum saturation difference value is denoted by Δ

C_max and a minimum saturation difference value is denoted by Δ

C_min, then a difference Δ

C_max −

Δ

C_min between the maximum saturation difference value and the minimum saturation difference value satisfies

3.0≦

Δ

C_max −

Δ

C_min≦

19.6.

4. The light-emitting device according to claim 1, wherein

(2) if hue angles in CIE 1976 L*a*b* color space of the 15 Munsell renotation color samples when mathematically assuming illumination by the light emitted from the light-emitting device in the radiant direction are denoted by θ

_nSSL (degrees) (where n is a natural number from 1 to

     15), and

hue angles in a CIE 1976 L*a*b* color space of the 15 Munsell renotation color samples when mathematically assuming illumination by a reference light that is selected according to the correlated color temperature T_SSL (K) of the light emitted in the radiant direction are denoted by θ

_nref (degrees) (where n is a natural number from 1 to

     15), then an absolute value of each difference in hue angles |Δ

h_n | satisfies

0≦

|Δ

h_n | ≦

9.0 (degrees) (where n is a natural number from 1 to

     15),

where Δ

h_n =θ

_nSSL −

θ

_nref.

5. The light-emitting device according to claim 1, wherein a luminous efficacy of radiation K (lm/W) in a wavelength range from 380 nm to 780 nm as derived from the spectral power distribution φ

_SSL (λ

) of light emitted from the light-emitting device in the radiant direction satisfies

180 (lm/W)≦

K (lm/W)≦

320 (lm/W).

6. The light-emitting device according to claim 1, wherein the correlated color temperature T_SSL (K) satisfies

2550 (K)≦

T_SSL (K)≦

7000 (K).

7. The light-emitting device according to claim 1, wherein illuminance at which the light emitted from the light-emitting device in the radiant direction illuminates objects is 150 lx to 5000 lx.

8. The light-emitting device according to claim 1, wherein the light-emitting device comprises a semiconductor light-emitting element as a light-emitting element and emits, in the radiant direction, light emitted from one to six light-emitting elements including the light emitted by the semiconductor light-emitting element.

9. The light-emitting device according to claim 8, wherein the peak wavelength of the emission spectrum of the semiconductor light-emitting element is 455 nm or longer and shorter than 485 nm.

10. The light-emitting device according to claim 8, wherein the peak wavelength of the emission spectrum of the semiconductor light-emitting element is 420 nm or longer and shorter than 455 nm.

11. The light-emitting device according to claim 1, comprising a phosphor as a light-emitting element.

12. The light-emitting device according to claim 11, wherein the phosphor includes one to five phosphors each having different emission spectra.

13. The light-emitting device according to claim 11, wherein the phosphor includes a green phosphor and a red phosphor.

14. The light-emitting device according to claim 13, wherein the green phosphor has an individual emission spectrum, when photoexcited at room temperature, with a peak wavelength of 495 nm or longer and shorter than 590 nm and a full-width at half-maximum of 2 nm to 130 nm.

15. The light-emitting device according to claim 13, wherein the red phosphor has an individual emission spectrum, when photoexcited at room temperature, with a peak wavelength of 590 nm or longer and shorter than 780 nm and a full-width at half-maximum of 2 nm to 130 nm.

16. The light-emitting device according to claim 13, wherein the green phosphor is a narrow band green phosphor.

17. The light-emitting device according to claim 13, wherein the green phosphor is β

-SiAlON.

18. The light-emitting device according to claim 13, wherein the red phosphor is SCASN.