Outdoor luminaire

Abstract

An outdoor luminaire comprising a blue LED chip having a maximum peak at a wavelength of 420-480 nm and a phosphor layer disposed forward of the LED chip in its emission direction is provided. The phosphor layer comprises a phosphor of the formula: Lu.sub.3Al.sub.5O.sub.12:Ce.sup.3+ which is activated with up to 1 mol % of Ce relative to Lu, the phosphor being dispersed in a resin. In scotopic and mesopic vision conditions, the luminaire produces illumination affording brighter lighting, higher visual perception and brightness over a broader area.

Claims

1. An outdoor luminaire comprising a blue LED chip having a maximum peak at a wavelength of 420 to 480 nm and a phosphor layer disposed forward of the LED chip in its emission direction, said phosphor layer comprising a phosphor mixed and dispersed in a resin, the phosphor having the compositional formula (1):
Lu.sub.3Al.sub.5O.sub.12:Ce.sup.3+(1) and a Ce-activation rate relative to Lu of up to 1 mol %, and the phosphor being obtained by a method comprising the step of mixing lutetium oxide, cerium oxide and aluminum oxide in powder form, and heating the mixture in air, an inert atmosphere or a reducing atmosphere to form a complex oxide, and disintegrating the complex oxide, wherein the luminaire provides light having an intensity S1 at wavelength 510 nm and an intensity S2 at wavelength 545 nm, the ratio of S1/S2 being at least 0.95, and the phosphor layer comprises the phosphor of at least 0.1% and up to 50% by weight of the phosphor layer.

2. The luminaire of claim 1 wherein the resin is a silicone resin or epoxy resin.

3. The luminaire of claim 1 wherein the resin is at least one thermoplastic resin selected from the group consisting of polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polycarbonate, polystyrene, and ABS resin.

4. The luminaire of claim 1 which provides the light having the ratio of S1/S2 being at least 1.

5. The luminaire of claim 1 wherein the phosphor layer is spaced apart from the blue LED chip.

6. The luminaire of claim 1 wherein said Ce-activation rate relative to Lu is at least 0.1 mol %.

7. The luminaire of claim 1 which is a streetlight or light for a pathway, roadway, plaza, outdoor residential area or tunnel.

8. The luminaire of claim 1, wherein in the heating step, the mixture is heated in air or an inert atmosphere.

9. A method of outdoor illumination using an outdoor luminaire comprising a blue LED chip having a maximum peak at a wavelength of 420 to 480 nm and a phosphor layer disposed forward of the LED chip in its emission direction, said phosphor layer comprising a phosphor mixed and dispersed in a resin, the phosphor having the compositional formula (1):
Lu.sub.3Al.sub.5O.sub.12:Ce.sup.3+(1) and a Ce-activation rate relative to Lu of up to 1 mol %, and the phosphor being obtained by a method comprising the step of mixing lutetium oxide, cerium oxide and aluminum oxide in powder form, and heating the mixture in air, an inert atmosphere or a reducing atmosphere to form a complex oxide, and disintegrating the complex oxide, wherein the phosphor layer comprises the phosphor of at least 0.1% and up to 50% by weight of the phosphor layer.

10. The method of claim 9 wherein the resin is a silicone resin or epoxy resin.

11. The method of claim 9 wherein the resin is at least one thermoplastic resin selected from the group consisting of polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polycarbonate, polystyrene, and ABS resin.

12. The method of claim 9 wherein the luminaire provides light having an intensity S1 at wavelength 510 nm and an intensity S2 at wavelength 545 nm, the ratio of S1/S2 being at least 0.95.

13. The method of claim 12 wherein the luminaire provides light having the ratio of S1/S2 being at least 1.

14. The method of claim 9 wherein the luminaire of remote phosphor type in which the phosphor layer is spaced apart from the blue LED chip.

15. The method of claim 9 wherein said Ce-activation rate relative to Lu is at least 0.1 mol %.

16. The method of claim 9, wherein the luminaire is a streetlight or light for a pathway, roadway, plaza, outdoor residential area or tunnel.

17. The method of claim 9, wherein in the heating step, the mixture is heated in air or an inert atmosphere.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a diagram showing the X-ray diffraction (XRD) profile of Lu.sub.3Al.sub.5O.sub.12:Ce.sup.3+ phosphor in Example 1.

(2) FIG. 2A and FIG. 2B illustrate an LED luminaire manufactured in Examples and Comparative Examples, (A) being a partly cut-away plan view and (B) being a perspective view.

(3) FIG. 3 is a diagram showing the spectral profile of emission from an LED luminaire of Example 1.

(4) FIG. 4 is a diagram showing the spectral profile of emission from an LED luminaire of Comparative Example 1.

(5) FIG. 5 is a diagram showing the luminescent spectral profile of Lu.sub.3Al.sub.5O.sub.12:Ce.sup.3+ phosphor in Comparative Example 3 in response to excitation light of wavelength 450 nm.

(6) FIG. 6 is a diagram showing the spectral profile of emission from an LED luminaire of Comparative Example 3.

(7) FIG. 7 is a diagram showing the emission spectrum (broken line) of a general white LED, and the peak wavelength (555 nm) in bright room and the peak wavelength (507 nm) in dark room of human eye sensitivity.

DESCRIPTION OF PREFERRED EMBODIMENTS

(8) One embodiment of the invention is an outdoor luminaire (or lighting equipment) comprising a blue LED chip having a maximum peak in the wavelength range of 420 to 480 nm. The blue LED chip may be a well-known blue LED package in which a blue LED chip, wirings and the like are sealed with an encapsulant. Any of well-known or commercially available blue LED packages may be used. Those blue LED chips having a maximum peak at a shorter or longer wavelength than the wavelength range defined above are undesirable because the excitation efficiency of phosphor is extremely reduced.

(9) The outdoor luminaire also comprises a phosphor layer which is disposed forward of the blue LED chip in its emission direction. The phosphor layer has a phosphor mixed and dispersed in a resin, the phosphor having the compositional formula (1):
Lu.sub.3Al.sub.5O.sub.12:Ce.sup.3+(1)
and a Ce-activation rate relative to Lu (i.e., a proportion of Ce based on the sum of Lu and Ce) of up to 1 mol %, preferably at least 0.1 mol %. This phosphor is often referred to as LuAG phosphor. Preferably the phosphor layer contains at least 0.1% by weight and up to 50% by weight of the LuAG phosphor of formula (1).

(10) If the Ce-activation rate relative to Lu exceeds 1 mol %, a proportion of 5d.fwdarw..sup.2F.sub.7/2 transition becomes higher than a proportion of 5d.fwdarw..sup.2F.sub.5/2 transition, the peak position of emission spectrum shifts toward the longer wavelength side, and the emission wavelength largely deviates from the visual sensitivity under scotopic or mesopic vision, resulting in lighting with poor brightness under scotopic or mesopic vision. If the Ce-activation rate relative to Lu is less than 0.1 mol %, the phosphor itself has a poor absorptivity with the risk that light near wavelength 510 nm giving bright perception under scotopic or mesopic vision may become short.

(11) The LuAG phosphor used herein is in particulate form. From the aspect of emission efficiency, the phosphor particles preferably have an average particle size of 1.5 to 50 microns (m). If the average particle size is less than 1.5 m, the emission efficiency of phosphor may lower, with a drop of lighting efficiency. If the average particle size exceeds 50 m, this raises no problems with respect to lighting characteristics, but a larger amount of phosphor must be used to increase the number of particles, undesirably leading to an increased cost. The particle size of phosphor particles may be determined, for example, by dispersing phosphor particles in a gas or water stream and measuring their size by the laser diffraction scattering method.

(12) The LuAG phosphor used herein may be prepared by well-known methods. For example, lutetium oxide, cerium oxide and aluminum oxide in powder form are mixed in such amounts as to meet the desired composition. Barium fluoride is added thereto as a flux. The powder mixture is heated at a high temperature in air, an inert atmosphere (e.g., nitrogen) or reducing atmosphere (e.g. argon partly replaced by hydrogen) to form a complex oxide, which is disintegrated on a ball mill or the like to an appropriate size.

(13) In the phosphor layer, a phosphor other than the LuAG phosphor of formula (1) may be used for the purposes of improving the tone and color rendering of outdoor lighting as long as the objects of the invention are not impaired.

(14) The resin of the phosphor layer may be either transparent or semi-transparent. For example, silicone resins and epoxy resins may be used. The phosphor layer may be formed by mixing and dispersing phosphor particles in an uncured resin composition, applying the resin composition to the surface of a blue LED chip or package, and curing the resin composition. Alternatively, a phosphor-loaded resin composition may be molded and cured to form a phosphor layer, which is disposed forward of a blue LED chip or package in its emission direction.

(15) In another preferred embodiment, the resin of the phosphor layer is a thermoplastic resin selected from among polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polycarbonate, polystyrene, and ABS resin, alone or in admixture of two or more. Where a thermoplastic resin is used, a phosphor layer may be formed by milling phosphor particles with the thermoplastic resin for thereby dispersing the phosphor in the resin, and molding the resin, and the phosphor layer be disposed forward of a blue LED chip or package in its emission direction.

(16) For shaping of the phosphor layer, any well-known molding methods such as compression molding, extrusion molding and injection molding may be used. The material may be molded to any desired shape such as film or thin plate and to any desired size. The shape and size of the phosphor layer may be selected as appropriate depending on the application form of the phosphor layer. Typically the thickness of the phosphor layer is in a range of about 0.5 to 3 mm, though not particularly limited.

(17) Besides the phosphor and resin, additives may be used in the phosphor layer as long as the objects of the invention are not impaired. Suitable additives include auxiliary agents for improving weather resistance or preventing UV-induced degradation, such as radical scavengers and antioxidants, and light scattering agents for promoting light scattering, such as silica and talc. The content of such additive is typically up to 10% by weight, preferably 0.01 to 5% by weight of the phosphor layer.

(18) Preferably the outdoor luminaire takes the form of remote phosphor type in which the phosphor layer, especially the phosphor layer based on a thermoplastic resin is spaced apart from the blue LED package via a gas or vacuum layer.

(19) Since the luminaire of remote phosphor type has luminous intensity distribution characteristics different from general LED lamps, typically surface emission and a large radiation angle, it is particularly suited as the luminaire intended to provide illumination over a broad area.

(20) In a preferred embodiment, the outdoor luminaire produces light having an intensity S1 at wavelength 510 nm and an intensity S2 at wavelength 545 nm, wherein the ratio of S1/S2 is at least 0.95, more preferably at least 1. The luminaire is capable of complying with a change of visual sensitivity based on the Purkinje effect because the light is full of wavelengths giving a high visual sensitivity at scotopic and mesopic vision levels.

(21) The luminaire of the invention is suitable for installation in those areas with less brightness at night or where least light is available nearby, for example, pathways, roadways, plazas, residential areas, and tunnels. It is suitable for outdoor use, typically as streetlight. It may also be used indoor if the indoor area is in a similar dark environment, because it is suitable for use in scotopic and mesopic vision conditions.

EXAMPLE

(22) Examples and Comparative Examples are given below by way of illustration and not by way of limitation.

Example 1

(23) A powder mixture, 1,000 g, was obtained by mixing lutetium oxide (Lu.sub.2O.sub.3) powder of 99.9% purity having an average particle size of 1.0 m, aluminum oxide (Al.sub.2O.sub.3) powder of 99.0% purity having an average particle size of 0.5 m, and cerium oxide (CeO.sub.2) powder of 99.9% purity having an average particle size of 0.2 m in a molar ratio Lu:Al:Ce of 2.97:5.0:0.03. Barium fluoride, 200 g, as flux was added to the powder mixture, which was thoroughly mixed. The mixture was placed in an alumina crucible and heat treated in argon gas at 1,400 C. for 10 hours. The fired product was disintegrated on a ball mill, washed with about 0.5 mol/L hydrochloric acid and then with deionized water. Subsequent solid/liquid separation and drying yielded Lu.sub.3Al.sub.5O.sub.12:Ce.sup.3+ phosphor particles (Ce-activation rate relative to Lu is 1 mol %) having an average particle size of 20 m.

(24) The result of XRD analysis of the phosphor particles is shown in FIG. 1. The diffraction pattern of main phase of the phosphor particles is coincident with the diffraction peaks of lutetium aluminum garnet phase, demonstrating that Lu.sub.3Al.sub.5O.sub.12:Ce.sup.3+ containing garnet phase as main phase is obtained.

(25) The Lu.sub.3Al.sub.5O.sub.12:Ce.sup.3+ phosphor particles were dispersed in a transparent epoxy resin (SpeciFix-40 kit by Marumoto Struers K.K.) to form a slurry having a phosphor concentration of 20 wt %. The slurry was added dropwise to the emissive surface of a blue LED package (NS6b083T by Nichia Corp.) and cured at 50 C. for 3 hours, completing an LED package having a phosphor layer containing phosphor particles mixed and dispersed in epoxy resin.

(26) Seven LED packages thus manufactured were arranged in a rectangular aluminum chassis of 39 mm wide, 220 mm long, and 30 mm deep (inside size) and connected in series. A transparent matt acrylic plate of 2 mm thick as a protective cover was attached at a position spaced 25 mm apart from the emissive surface of the LED packages. An LED luminaire was fabricated as shown in FIG. 2, wherein LED packages 1, aluminum chassis 2, protective cover 3, power supply terminals 4, and power switch 5 are depicted.

(27) The spectrum of illuminating light of the LED luminaire was measured by an illuminance spectrophotometer CL-500 (Konica Minolta, Inc.). The result is shown in FIG. 3. In the spectrum, an intensity S1 at wavelength 510 nm and an intensity S2 at wavelength 545 nm were measured, from which a ratio S1/S2 was calculated to be 1.076.

Example 2

(28) A powder mixture, 1,000 g, was obtained by mixing yttrium oxide (Y.sub.2O.sub.3) powder of 99.9% purity having an average particle size of 1.0 m, aluminum oxide (Al.sub.2O.sub.3) powder of 99.0% purity having an average particle size of 0.5 m, and cerium oxide (CeO.sub.2) powder of 99.9% purity having an average particle size of 0.2 m in a molar ratio Y:Al:Ce of 2.94:5.0:0.06. Barium fluoride, 200 g, as flux was added to the powder mixture, which was thoroughly mixed. The mixture was placed in an alumina crucible and heat treated in argon gas at 1,400 C. for 10 hours. The fired product was disintegrated on a ball mill, washed with about 0.5 mol/L hydrochloric acid and then with deionized water. Subsequent solid/liquid separation and drying yielded Y.sub.3Al.sub.5O.sub.12:Ce.sup.3+ phosphor particles having an average particle size of 20 m.

(29) An LED package with a phosphor layer was manufactured as in Example 1 except that the Lu.sub.3Al.sub.5O.sub.12:Ce.sup.3+ phosphor particles in Example 1 and the Y.sub.3Al.sub.5O.sub.12:Ce.sup.3+ phosphor particles in Example 2 were dispersed in the transparent epoxy resin in an amount of 15 wt % and 5 wt %, respectively. Using the packages, an LED luminaire was similarly fabricated.

(30) The spectrum of illuminating light of the LED luminaire was measured as in Example 1. The intensity ratio S1/S2 was 0.983.

Example 3

(31) Seven blue LED packages (XLamp LX-E Royal Blue by Cree Inc.) were arranged in an aluminum chassis and connected in series as in Example 1. The Lu.sub.3Al.sub.5O.sub.12:Ce.sup.3+ phosphor particles in Example 1 were kneaded in polycarbonate in a phosphor concentration of 5 wt %, and the resulting PC compound was molded into a PC plate of 2 mm thick. This PC plate as the phosphor layer was attached at a position spaced 25 mm apart from the emissive surface of the blue LED packages. An LED luminaire of remote phosphor type was fabricated as shown in FIG. 2, wherein the protective cover 3 also serves as a phosphor layer.

(32) The spectrum of illuminating light of the LED luminaire was measured as in Example 1. The intensity ratio S1/S2 was 1.067.

Comparative Example 1

(33) An LED package with a phosphor layer was manufactured as in Example 1 except that the phosphor used was the Y.sub.3Al.sub.5O.sub.12:Ce.sup.3+ phosphor particles in Example 2 alone. Using the packages, an LED luminaire was similarly fabricated.

(34) The spectrum of illuminating light of the LED luminaire was measured by the spectrophotometer CL-500, with the result shown in FIG. 4. In the spectrum, an intensity S1 at wavelength 510 nm and an intensity S2 at wavelength 545 nm were measured, from which a ratio S1/S2 was calculated to be 0.668.

Comparative Example 2

(35) Seven white LED packages (XLamp LX-E Cool White by Cree Inc.) were arranged in an aluminum chassis and connected in series as in Example 1. A transparent matt acrylic plate of 2 mm thick as a protective cover was attached at a position spaced 25 mm apart from the emissive surface of the LED packages. An LED luminaire was fabricated as shown in FIG. 2.

(36) The spectrum of illuminating light of the LED luminaire was measured as in Example 1. The intensity ratio S1/S2 was 0.657.

Comparative Example 3

(37) A powder mixture, 1,000 g, was obtained by mixing lutetium oxide (Lu.sub.2O.sub.3) powder of 99.9% purity having an average particle size of 1.0 m, aluminum oxide (Al.sub.2O.sub.3) powder of 99.0% purity having an average particle size of 0.5 m, and cerium oxide (CeO.sub.2) powder of 99.9% purity having an average particle size of 0.2 m in a molar ratio Lu:Al:Ce of 2.94:5.0:0.06. Barium fluoride, 200 g, as flux was added to the powder mixture, which was thoroughly mixed. The mixture was placed in an alumina crucible and heat treated in argon gas at 1,400 C. for 10 hours. The fired product was disintegrated on a ball mill, washed with about 0.5 mol/L hydrochloric acid and then with deionized water. Subsequent solid/liquid separation and drying yielded Lu.sub.3Al.sub.5O.sub.12:Ce.sup.3+ phosphor particles (Ce-activation rate relative to Lu is 2 mol %) having an average particle size of 20 m.

(38) The phosphor particles were analyzed by XRD. The diffraction pattern of main phase of the phosphor particles is coincident with the diffraction peaks of lutetium aluminum garnet phase, demonstrating that Lu.sub.3Al.sub.5O.sub.12:Ce.sup.3+ containing garnet phase as main phase is obtained.

(39) The luminescent spectrum of this phosphor in response to excitation light of wavelength 450 nm was measured by the spectrophotometer CL-500, with the result shown in FIG. 5. This phosphor's emission peak near wavelength 510 nm was lower than at wavelength 545 nm.

(40) An LED package with a phosphor layer was manufactured as in Example 1 except that the phosphor used was the Lu.sub.3Al.sub.5O.sub.12:Ce.sup.3+ phosphor particles (Ce-activation rate relative to Lu is 2 mol %) in Comparative Example 3. Using the packages, an LED luminaire was similarly fabricated.

(41) The spectrum of illuminating light of the LED luminaire was measured by the spectrophotometer CL-500, with the result shown in FIG. 6. In the spectrum, an intensity S1 at wavelength 510 nm and an intensity S2 at wavelength 545 nm were measured, from which a ratio S1/S2 was calculated to be 0.939.

(42) The LED luminaires of Examples 1 to 3 and Comparative Examples 1 to 3 were mounted at the top of posts along an asphalt roadway at a height of 3 m, and burned at night by applying a voltage of 24 V. The road surface and adjacent objects were visually observed. The LED luminaires of Examples were superior to the LED luminaires of Comparative Examples in that the space looked bright, shadows were less, and adjacent objects were clearly seen.

(43) It has been demonstrated that the LED luminaires of Examples are excellent outdoor luminaires in that they produce effective lighting providing improved visual perception over a broader space including brightness of the overall space and brightness at the adjacent region. The LED luminaire of remote phosphor type in Example 3 provides surface emission, and due to an accordingly wide spread of illumination, non-glare lighting with less shadows is available. Since the luminaire of the invention produces lighting capable of complying with a change of visual sensitivity based on the Purkinje effect under scotopic and mesopic vision conditions, it is best suited for outdoor lighting.

(44) Japanese Patent Application No. 2013-132462 is incorporated herein by reference.

(45) Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims.