FIELD

The present invention relates to a light fixture and a light. Particularly, but not exclusively, the present invention relates to a light fixture and light for use on a boat either near the surface of water or under the surface of water.

BACKGROUND

In the underwater environment light undergoes substantially higher attenuation than it does above water. This means that in the underwater environment light needs to be provided at a much higher intensity which places on the underwater light source a requirement that the light output from a light source needs to be far greater than above water. The requirement for such a light output means that light sources when in operation at or below the surface of water generate considerable heat which can cause light sources to be inefficient and prone to burn out when the light source exceeds the maximum temperature at which it can operate. Aspects and embodiments were devised with the foregoing in mind.

SUMMARY

A light fixture is provided in accordance with a first aspect which can be used on a light which may be used on a boat but can also be used on any other craft and marinas, docks, swimming pools, fountains etc, where there is a requirement for light to be provided to an underwater environment.

In accordance with the first aspect, there is provided a light fixture comprising a light source mounted to a first side of a thermally conductive plate shaped to form a recessed portion where the light source is mounted and a surrounding wall portion which forms the bezel for the light fixture.

A light fixture in accordance with the first aspect provides a thermally conductive bezel for the light source that enables heat to be efficiently transferred from the light source to the external environment. In the underwater environment, this provides a fast and efficient transfer of heat as a thermal path is provided between the light fixture and the underwater environment which provides substantial cooling to the light fixture. This means that a high light output can be maintained whilst the risk that the light source will burn out is reduced.

The plate enables the light fixture to maintain a flatter profile which increases the efficiency of the transfer of heat between the light source and the external environment. Constructing the light fixture using a plate formed from a thermally conductive material reduces the amount of wasted material as a result of the manufacturing process as the plate can be cut from a larger sheet of the thermally conductive material and is then spun or pressed into shape without the substantial loss of material. The plate may be made from a material of high thermal conductivity such as copper, aluminium or graphite. Using a high thermal conductivity material increases the rate at which heat is transferred from the light source to the external environment which increases the cooling capability of the light fixture. The use of high thermal conductivity material also enables a much thinner thermal path to be created behind the light source which reduces the required amount of material behind the heat source and improves the thermal path into the surface area in contact with water in the underwater environment.

A high thermal conductivity material with a thermal conductivity above 200 watts per Meter Kelvin is particularly advantageous as the speed of heat transfer between the light source and the external environment is increased. An example of a material of this type is aluminium or copper.

The use of copper as the thermally conductive material is particularly suitable for use on a light fixture in accordance with the present invention as it exhibits a high thermal conductivity (approximately 400 watts per Meter Kelvin) and it also allows the light source to be brazed directly to the thermally conductive structure. Brazing reduces the thermal resistance between the light source and the thermally conductive plate which provides a more efficient thermal path when compared to, say, a thermal paste. The thermally conductive plate of the light fixture in accordance with the first aspect may be the first layer of a heat-pipe comprising a chamber at least partially filled with a working fluid. The working fluid may be water under vacuum, alcohol or acetone. The heat-pipe may further comprise a wick structure, which may be sintered copper, surrounding the chamber to absorb the working fluid when the working fluid is in the form of a vapour.

The use of a heat pipe provides a thermally conductive structure which operates at thermal conductivities an order of magnitude over materials such as copper. The chamber comprises first and second copper walls where the light source may be brazed to the first copper walls.

In accordance with the first aspect, the thermally conductive plate may form a printed circuit board for the light source. This removes the thermal interface between the light source and the thermally conductive structure and improves the thermal path between the light source and the surrounding water and also reduces the parts required for the light fixture.

A light fixture in accordance with the first aspect may further comprise a thin plastic body portion affixed to the thermally conductive plate to form an exterior part of the light fixture. In the underwater environment this is particularly advantageous as the plastic protects the thermally conductive plate from the corrosive effects of seawater . Plastic is also a much cheaper material than metal so the lights can be produced more cost effectively.

The combination of the thermally conductive plate and the thin plastic portion greatly improves the thermal conductivity of the light fixture as a whole. Placing the thermal conductive plate into contact with the plastic portion means that the heat will travel through the plastic portion and into the surrounding water. This enables lights of much higher power levels to be achieved whilst the light fixture is still protected from the corrosive effects of the seawater. . The thin plastic body portion may be in direct contact with the thermally conductive plate which increases the speed at which the heat is transferred to the external environment. The thin plastic body portion may also be shaped to match the shape of the thermally conductive plate.

A light fixture in accordance with the first aspect may also comprise driver electronics for the light source mounted to a second side of the thermally conductive structure. This enables the driver electronics to be cooled in the same way as the light source. The use of a second side of the thermally conductive structure also reduces the number of components required by the light fixture and the size of the components required by the light fixture. By providing heat management of the driver electronics in this manner, the lifetime of the driver electronics is increased and the efficiency of the driver electronics is also increased.

DESCRIPTION

First, second and third embodiments of the present invention will now be described by way of example only with reference to the following figures in which: Figure 1 schematically illustrates a cross-sectional view of a light fixture in accordance with a first embodiment of the present invention;

Figure 2 schematically illustrates a cross-sectional view of a light fixture in accordance with a second embodiment of the present invention;

Figure 3a schematically illustrates a cross-sectional view of a heat-pipe in accordance with the first or second embodiments of the present invention;

Figure 3b schematically illustrates the structure of the heat-pipe in accordance with an embodiment of the present invention;

Figure 4 schematically illustrates a thin body portion fitted to a light portion in accordance with an aspect of the present invention; and Figure 5 schematically illustrates a light fixture in accordance with a third embodiment of the present invention.

We will now describe a light fixture 100 in accordance with the embodiment with reference to Figure 1. Figure 1 illustrates a cross-sectional view of the light fixture 100 for simplicity but it will be understood that the light fixture 100 is a three dimensional object which is described in this way for clarity.

Light fixture 100 comprises a circular copper plate 102, a printed circuit board (PCB) 104 and an array of light emitting diodes (LEDs) 106. Copper plate 102 forms a bezel for the light fixture 100 and comprises a first recessed portion 108 on a first side of the copper plate 102 and a walled portion 1 10. The plurality of LEDs 106 are mounted to the PCB 104 which is brazed to the copper plate 102 in the recessed portion 108.

Using copper for plate 102 is a particularly advantageous choice of material as it exhibits a very high thermal conductivity and also allows the PCB 104 to be brazed directly to the copper plate 102. The use of brazing to mount the PCB 104 to the copper plate 102 reduces the thermal resistance between the LEDs 106 and the copper plate 102.

The copper plate 102 may be stamped from a sheet of copper. This means that the manufacture of the copper plate is less wasteful than current manufacturing processes that require substantially more material and produce substantially higher levels of waste.

The use of plate 102 as the bezel for the light fixture also provides a larger contact area with the external environment which increases the rate at which the heat is transferred from the LEDs 106 to the external environment, which could be underwater. To achieve this, although copper is particularly advantageous due to its high thermal conductivity and the reduced thermal resistance that can be enabled by the brazing, other metals can be used for the plate such as aluminium and other materials such as graphite sheet can also be used. If other materials are used for the plate then the LEDs 106 are attached to the plate 102 using a suitable mechanical or adhesive attachment. The plate 102 can be coated with paint or an anti-corrosive coating such as electroless nickel plating which adds aesthetic appeal whilst enhancing life underwater.

In accordance with a second embodiment, we describe how the driver electronics 1 12 for the LEDs 106 may be brazed to a second recessed portion 114 of the copper plate 102 with reference to Figure 2. Driver electronics 1 12 may be brazed to the side of the copper plate 102 opposite to the side where the LEDs are brazed. Holes may be machined through plate 102 to connect the driver electronics 112 to the LEDs.

In sharing the plate 102 with the LEDs 106 in the manner described above the driver electronics 1 12 can use the same heat transfer capabilities of the copper plate 102 to transfer the considerable heat they may generate. This means that if the light fixture 100 is used in the underwater environment the driver electronics 112 also benefit from the cooling effect provided by the water to the LEDs 106.

Brazing the driver electronics 1 12 to the other side of the copper plate 102 also makes installation of the light fixture 100 easier as the requirement to install a separate driver to control the LEDs 106 is removed.

Optionally or additionally, copper plate 102 may be the first layer of a heat-pipe 300 as we now describe with reference to Figure 3a.

Heat-pipe 300 comprises first copper plate 302 and second copper plate 304 which are hermetically sealed together around their respective edges to form a chamber 306. Water-under-vacuum 308 and a wick material 310 is placed inside the chamber 306 formed by the hermetic seal of the first copper plate 302 and the second copper plate 304. The wick material 310 is sintered copper but other suitable materials can be used .

The use of a heat-pipe 300 provides thermal conductivity capabilities which are an order of magnitude above the use of a copper plate 102. The heat from the LEDs 106 is conducted through the first copper layer 302 to the chamber 306 in the direction of arrow A. As a result of the heat from the LEDs, the water-under-vacuum 308 vaporises and the vapour travels along the chamber 306 in the direction of arrow B to a colder part of the chamber 306 (as illustrated by the arrow) which causes the water-under-vacuum 308 to condense back to a liquid, in turn releasing the latent heat stored inside the vapourised water-under-vacuum 308.

The colder part of the chamber 306 is described with reference to Figure 3b. The liquid formed by the condensation of the water-under vacuum 308 is then absorbed by the layer of sintered copper 310 in the chamber 306 which acts as a capillary to transfer the liquid back to the hotter part of the chamber in the direction of arrow C. The heat released by the condensation of the liquid back to water-under-vacuum is then conducted through the first copper wall 302 to the exterior of the light fixture 100 in the direction of arrow D.

The use of water-under-vacuum as the working fluid of the heat pipe 300 is particularly advantageous as it has a boiling point significantly lower than water which facilities expedient vapourisation at the levels of heat transferred into the chamber 306 by the LEDs. Acetone or alcohol may also be used as the working fluid of the heat pipe 300. Acetone and alcohol also have a boiling point significantly lower than water.

We now describe how the light fixture 100 of any of the other embodiments may be covered with a thin plastic body portion with reference to Figure 4.

Figure 4 schematically illustrates the light fixture 400 comprising a thin plastic body portion 402 comprising a transparent central portion 404 to enable light emitted by the LEDs 106 to pass through.

Body portion 402 is shaped to match the plate 102 and is placed into direct contact with the plate 102 which enables the heat conducted through the plate 102 to be transmitted to the body portion 402. The dimensionality of the body portion 402, i.e. that it is thin, means that heat will pass through the body portion 402 which improves the heat management capabilities of the light fixture 400. As the body portion 402 is made from plastic, the light fixture 400 is protected from the corrosive effects of the water in the underwater environment.

In a third embodiment, the plate 102 may form a PCB for the LEDs 106 and/or the driver electronics 1 12 as illustrated in Figure 5. This reduces the thermal path between the plate and the respective driver electronics 1 12 and/or LEDs 106. A reduced thermal path between the plate and the respective driver electronics and/or LEDs 106 increases the heat transfer capability of the light fixture 100.

Light fixture 100 may be used on the side or underside of a boat to provide underwater lighting. The use of the copper plate 102 to efficiently transfer heat from the LEDs to the exterior of the light enables the LEDs to be cooled by the surrounding water.

The simplicity and profile of light fixture 100 provides a light fixture that can be cooled speedily and efficiently while providing an intensity of light that is necessary for lighting in the underwater environment.