AU4252499A - An in ground light - Google Patents

Description

WO 99/64783 PCT/AU99/00464 AN IN GROUND LIGHT Technical Field This invention relates to in ground lights or luminaries. 5 Background Art Lights of this kind are frequently used for up lighting trees or architectural elements from below. Typically these up lighting luminaires are flush mounted in a paved surface and are designed to withstand traffic loads including moderate vehicle traffic 10 loads. It is a requirement that luminaires of this type meet the design standards applicable to totally submersible luminaires. The Australian standard is AS 1939 classification IP68. In order to be totally submersible the casings of the luminaires must be totally sealed 15 to water penetration. The difficulties in dissipating heat generated by the light source result in the exposed lens reaching temperatures high enough to cause injury on contact. Lens temperatures of the order of 120 0 C are not uncommon. Disclosure of the Invention 20 It is an object of this invention to provide an in ground luminaire in which the temperature of the exposed lens is reduced. Accordingly, in one aspect this invention provides an in ground luminaire including a sealed housing closed at or adjacent one end by a first light transmitting lens, a light 25 source disposed in said housing, and a second light transmitting lens extending across the housing between said source and said first lens and, spaced apart from said first lens to attenuate the transmission of heat to the volume between the first and second lens and reduce the conductive heating of the first lens. 30 In one form of the invention, the second lens preferably substantially seals with the housing to seal the insulating volume from the remainder of the housing containing the WO 99/64783 PCT/AU99/00464 -2 light source. It is not essential that the second lens forms an air tight seal but rather it is preferred that it substantially prevents the flow of air between the area immediately adjacent the light source and the remainder of the housing. 5 Preferably a reflector is disposed about the light source on the side remote from said first lens. In a second form of the invention the reflector directs visible light toward said first lens and transmits a substantial portion of incident infrared radiation toward the housing. 10 In the second form the second lens is preferably adjacent the reflector. The reflector is preferably a Dichroic glass reflector. In both forms of the invention the second lens is preferably positioned adjacent the light source. 15 In one form of the invention utilising a 50 watt cool beam lamp has been found to result in the temperature of the first lens not exceeding about 650C during operation of the luminaire. The temperature difference between the first and second lenses (that is gradient across the insulating volume) is preferably at least about 600C and may be 20 up to 100'C. The housing is preferably formed of a metal having a relatively high thermal conductivity to assist in the dissipation of heat to the material surrounding the luminaire. One suitable housing material is cast bronze. 25 The luminaire according to this invention has an external lens that operates at a temperature sufficiently reduced from the prior art arrangements that burning contact injury by the lens at least is avoided. In this regard the operating temperature of the lens may be sufficiently high to cause burning of the skin in prolonged contact. 30 However, temperature is sufficiently low to normally allow the lens to be touched by the human hand and withdrawn on realisation of its temperature without significant WO 99/64783 PCT/AU99/00464 -3 damage. Typically this requires a lens temperature of less than around 650C. The invention will now be described, by way of example only, with reference to the accompanying drawings. 5 Brief Description of the Drawings Figure 1 is a first schematic cross section of an in ground luminaire of a first embodiment of this invention shown installed in a concrete slab; Figure 2 is a second schematic cross section at 900 to the section of Figure 1 (not 10 showing the concrete slab); Figure 3 is a plan view of the luminaire shown in Figures 1 and 2; and Figure 4 is a schematic cross section of an in ground luminaire according to a second embodiment of the invention. 15 Best Modes for Carrying out the Invention A first embodiment of a luminaire or light according to this invention is shown in Figures 1 to 3. The luminaire or light 1 includes a cylindrical housing 2 cast a single unit from bronze. The light 1 is shown installed in a concrete slab C in Figure 1. The housing 2 is closed at an open end by a borosilicate tempered lens 3 which is sealed 20 to the housing by a rubber seal 4 fitted between the lens 3 and an annular seat 5 in the housing 2. An annular retaining ring 6 secures the lens 3 to the housing 2 by means of screws 7. A light source indicated generally at 8 is fitted within the housing remote from the lens 2. The light source 8 includes a dichroic glass reflector 9 within which a lamp (not shown) is located and associated connector 10. The dichroic 25 reflector reflects visible light toward lens 3 and transmits infrared radiation toward the housing for dissipation. The mounting of the lens 3 in a sealing manner with housing 2 is a standard expedient used in the field and does not need to be described in detail for a full understanding 30 of the invention. Electrical power is supplied to the housing by electrical wires 12, 13, which pass through a sealing connection 11.

WO 99/64783 PCT/AU99/00464 -4 A second lens 14 of borosilicate tempered glass is supported adjacent reflector 9 by means of a retaining bracket 15. The bracket 15 has a pair of inwardly directed annular spaced apart flanges 16, 17 which captively engage the outer periphery of lens 14. The bracket 15 also includes an outwardly directed mounting lip 18 for 5 engagement with a supporting groove 19 in the housing 2. The lens 14 extends across the reflector 2 to slow down the transmission of heat from within the reflector to give time for dissipation by housing 2. The fitting of lens 14 close to reflector 9 prevents any significant air flow to the remainder of the housing. Consequently, the conductive heating of the outer lens 3 is significantly reduced. That is, the lens 16 10 confines the air heated by the light source 8 to the region immediately around the light source. As a result the air in insulating volume 20 provides comparatively good thermal insulation between lens 14 and lens 3. This in turn results in significantly less heating of the outer lens 3. In testing it has been found that under normal operating conditions a 50 watt light can continuously operate with the outer lens 3 reaching a 15 temperature of only about 65'C. It has been found that the internal lens 16 when formed of a material such as borosilicate glass is able to successfully withstand the temperatures generated due to its positioning closely adjacent the light source 8. Figure 4 shows a second embodiment of a luminaire according to this invention. The 20 luminaire or light 101 includes a cylindrical housing 102 cast a single unit from bronze. The housing 102 is closed at an open end by a borosilicate tempered lens 103 which is sealed to the housing by a rubber seal 104 fitted between the lens 103 and an annular seat 105 in the housing 102. An annular retaining ring 106 secures the lens 103 to the housing 102 by means of screws 107. A light source indicated generally 25 at 108 is fitted within the housing remote from the lens 103. The light source 108 includes a reflector 109 within which a lamp (not shown) is located and associated operating control gear 110. The mounting of the lens 103 in a sealing manner with housing 102 and the details of the light source 108 are standard expedients used in the field and do not need to be described in detail for a full understanding of the 30 invention. Electrical power is supplied to the housing via a connection 111 which is also of the kind known per se and will therefore not be described in detail.

WO 99/64783 PCT/AU99/00464 -5 The housing 102 includes a circumferentially arranged series of four webs, three of which 112, 113 and 114 are shown in the drawing. These webs extend along the inside walls of the housing 102 to provide mounting ledges 115, 116, 117 located between reflector 109 and lens 103. A second lens 118 of borosilicate or tempered 5 glass is supported from this ledge by means of a retaining ring 119. The ring 119 has a pair of inwardly directed annular spaced apart flanges 120, 121 which captively engage the outer periphery of lens 118. The retaining ring 119 also includes an outwardly directed mounting lip 123 for engagement with the supporting ledges 115, 116, 117. In this way the lens 118 extends across the volume of the housing 102 to 10 define an insulating volume of air 124 between the two lenses 103 and 118. The fitting of lens 118 into the retaining ring which in turn closely abuts the inside of the housing 102 prevents any significant air flow between the portion of the housing containing the light source 108 and volume 124. Consequently, the conductive heating of the outer lens 103 is significantly reduced. That is, the lens 118 confines 15 the air heated by the light source 108 to the region immediately around the light source. As a result the air in insulating volume 124 provides comparatively good thermal insulation between lens 118 and lens 103. This in turn results in significantly less heating of the outer lens 103. In testing it has been found that under normal operating conditions a 150 watt light can continuously operate with the outer lens 103 20 reaching a temperature of only about 60°C. It has been found that the internal lens 118 when formed of a material such as borosilicate glass is able to successfully withstand the temperatures generated due to its positioning closely adjacent the light source 108. 25 The foregoing describes only one embodiment of the invention and modifications can be made without departing from the scope of the invention.

Claims (10)

1. An in ground luminaire including a sealed housing closed at or adjacent one end by a first light transmitting lens, a light source disposed in said housing, and a second light transmitting lens extending across the housing between said source and said first lens and spaced apart from said first lens to attenuate the transmission of heat to the volume between the first and second lens and reduce conductive heating of the first lens.

2. An in ground luminaire as claimed in claim 1 wherein said second lens defines an insulating volume between the first and second lens.

3. An in ground luminaire as claimed in claim 2 wherein the second lens substantially seals with the housing to seal the insulating volume from the remainder of the housing containing the light source.

4. An in ground luminaire as claimed in claim 3 further including a reflector disposed about said light source on the side remote from said first lens.

5. An in ground luminaire as claimed in claim 4 wherein said reflector directs visible light toward said first lens and transmits a substantial portion of incident infrared radiation toward the housing.

6. An in ground luminaire as claimed in claim 5 wherein said reflector is a Dichroic glass reflector.

7. An in ground luminaire as claimed in claims 4 to 6 wherein said second lens is positioned adjacent said reflector.

8. An in ground luminaire as claimed in claims 1 to 7 wherein said second lens is positioned adjacent said light source. WO 99/64783 PCT/AU99/00464 -7

9. An in ground luminaire as claimed in claims 1 to 8 wherein said housing is formed from a metal of relatively high thermal conductivity.

10. An in ground luminaire as claimed in claims 1 to 9 wherein said first and second lens are formed of borosilicate glass.