This invention relates to light-emitting diode (LED) lighting apparatus and more particularly but not solely to hermetically sealed LED lighting apparatus for providing illumination in humid, underwater, explosive or other such adverse environments.

Hermetically sealed LED lighting apparatus for providing underwater illumination around vessels are well known. WO2016083787 discloses once such apparatus in the form of a luminaire for fixing to the hull of a yacht, the luminaire comprising a plurality of high power LED devices mounted in a chamber disposed inside a sealed body. The body has an optically transparent front wall that may comprise lenses, filters or other secondary optical elements. A problem of this arrangement is that operating LED devices in a sealed chamber can be a contributing factor leading to discoloration, lumen degradation and light output colour (CCT) shift of the LED devices.

Typically, high power LED devices of all types, regardless of manufacturer, have a dome-shaped primary lens formed of silicone that is disposed over the bare LED semiconductor or phosphor-coated LED semiconductor. In order to prevent degradation of the silicon dome, LED devices need to operate in an environment that contains oxygen. Tests have shown that LED devices operating in a hermetically sealed environment will eventually decay in performance. The rate of decay depends on a number of factors;

• Heat

• Photonic energy

• Oxygen availability

High performance (high lumen output) LED lighting apparatus in general suffer from all the above-mentioned issues, since their very nature means that they have high lumen output (high photonic energy) and operate at elevated temperatures owing to their high power consumption. The problem is further exacerbated in compact LED lighting apparatus because of the limited oxygen availability.

The silicone polymers used as encapsulants in LED devices comprise cross-linked poly-siloxane chains. During the curing process used to form such encapsulants, residual hydrocarbons and other by-products of the process remain within the structure of the silicone. As the LED device is operated, high energy photons emitted from the semiconductor cause some of the residual hydrocarbons remaining in the silicone to break-down. Normally, oxygen in the air will react with these residual hydrocarbon fragments, thereby preventing any potentially harmful effects.

If the LED devices are operated in a hermetically sealed chamber, for example behind secondary optical elements in LED lighting apparatus, there is a limited amount of oxygen initially present within the chamber to react with the quantity of hydrocarbons present in the silicone. Whilst the light emitted by the LED device will initially be normal, the available oxygen within the chamber will eventually be consumed as the reaction occurs. The resulting lack of oxygen will then cause discoloration in the silicone and the light output from the LED will be degraded. Re exposure of the LED device to air will result in recovery of the light output due to the fact that oxygen is now present to react with the hydrocarbons. It is known to provide LED lighting apparatus having an LED device that is able to breathe inside a hermetically sealed chamber through a semi-permeable vent of Gor -Tex (Registered Trade Mark) or other breathable material. The semi-permeable vent prevents water, dust or debris from entering the apparatus yet allows vapor diffusion and air to enter the chamber thus reducing condensation and ensuring the LED device has enough surrounding oxygen available to react with by-products for the acceptable lifetime of the apparatus.

Whilst such vents are waterproof, a problem is that they are not intended for permanent submersion because their adhesive backing and/or construction can fail over a short time when submerged. They also do not solve the issue of allowing air to travel into the LED chamber when the LED lighting apparatus is completely submerged because no fresh air can travel through the submerged vent into the LED chamber to replenish the oxygen levels.

With the foregoing problems in mind we have now devised an improved LED lighting apparatus.

In accordance with the present invention, as seen from a first aspect, there is provided LED lighting apparatus comprising a sealed body which defines a chamber and an LED device disposed in the chamber for emitting light through a translucent wall of the body, wherein an elongate gas flow duct extends from the chamber to a point disposed externally of the body.

In use, the sealed body prevents water, moisture, dust, debris and gasses from entering the chamber so that the apparatus can be used in humid, underwater, explosive or other adverse environments. However, the duct allows the flow of oxygen into the chamber from a remote point, in order to maintain the oxygen at a sufficient level inside the chamber to prevent the aforementioned degradation of the LED device without compromising the sealing of the body against the ingress of the surrounding environment. The sealed chamber remains watertight despite the duct.

The duct may comprise a proximal end which opens into the chamber and a distal end which is closed by a vent or other member which is permeable to oxygen. The distal end vent or other member allows oxygen to enter the duct yet prevents water, dust and other debris from entering the duct and potentially contaminating the chamber.

The duct may extend along a cable which conveys power to and/or signals to and/from the body of the apparatus. The duct may be disposed inside a sheath of the cable which surrounds both the duct and one or more electrical conductors disposed inside the sheath. The cable can be any length that is sufficient to allow the luminaire to be fully submerged whilst ensuring air can travel into the apparatus along the duct.

In a first embodiment, the distal end of the duct terminates at a formation disposed intermediate opposite ends of the cable. In a second embodiment, the distal end of the duct terminates at a connector provided on the distal end of the cable.

In a third embodiment, the distal end of the duct terminates in a unit to which the distal end of the cable is connected. The apparatus may be arranged to expel gasses along the duct from within the chamber as it heats up when the LED device is illuminated and to admit gasses from the atmosphere along the duct as it cools once the LED device is extinguished.

In use, when the LED device is illuminated, the apparatus heats up and the air inside the sealed chamber expands and builds pressure. This build-up of pressure forces air along the duct until it escapes to atmosphere, through any vent or other member on the distal end thereof until the pressure equalises.

When the LED device is extinguished, the apparatus cools and the air inside the sealed chamber contracts and fresh oxygenated air is drawn into the chamber. Also envisaged is a method of oxygenating an LED lighting apparatus in accordance with the first aspect of the present invention, the method comprising illuminating the LED device to heat gasses within the chamber such that the gasses are expelled from the chamber to atmosphere along the duct as the gasses expand, extinguishing the LED device such that air is drawn in from the chamber from atmosphere along the duct as the gasses within the chamber cool and contract.

Also in accordance with the present invention, as seen from a second aspect, there is provided LED lighting apparatus comprising a sealed body which defines a chamber and an LED device disposed in the chamber for emitting light through a translucent wall of the body, wherein a chemical compound is disposed within the body, the compound being arranged to react and produce oxygen for increasing the level of oxygen within the chamber, and wherein a catalyst is disposed within the body for increasing the rate of said chemical reaction.

The apparatus may be configured so that the compound slowly produces oxygen and thus prevents degradation of the light output for the acceptable lifetime of the apparatus. As oxygen is consumed by the reaction of air with the silicone, it is replaced at a similar rate by a chemical reaction extending the lifetime of the luminaire to an acceptable level.

The apparatus may be configured so that the compound produces oxygen at an increased rate when the LED device is illuminated by virtue of the generated heat or light output.

The compound may comprise hydrogen peroxide which will decompose slowly over time to form water and oxygen according to the following equation:

2H ₂ 0 ₂ (aq) 2H ₂ 0(i) + 0 ₂ (g)

The hydrogen peroxide may be provided as a liquid or a gel. The gel composition is understood to be a partially fluid substance. Over time and with the application of heat, the liquid component of the gel evaporates and the gel releases hydrogen peroxide which decomposes to provide oxygen. The advantage of the gel is that it does not need a container of any sort. It can be dispensed anywhere within the LED cavity and conform and adhere to its surroundings. This makes it very easy to apply and effectively retrofit the solution to existing products without product redesign. The gel can be dispensed on any surface and in any orientation, for example on top of the LED, in contact with the LED or creating a damn around the LED. The rate of chemical reaction can be controlled by the concentration of hydrogen peroxide, an increase in temperature or the presence of light.

For LED devices with higher photonic energy that use more oxygen content, the rate of reaction can be increased using a controlled amount of catalyst. The catalyst may be manganese oxide, which when added to hydrogen peroxide, causes bubbles of oxygen to be generated.

Yeast (available in tablet or powder form) is also another catalyst that can be added to hydrogen peroxide. The yeast serves as a catalyst for the chemical reaction. It speeds up the chemical decomposition reaction of the hydrogen peroxide but remains as yeast and does not chemically change itself.

In one embodiment, the chemical compound and any catalyst may be contained in a gas permeable capsule disposed within the chamber.

In another embodiment, the chemical compound may be disposed in a cavity formed within a heatsink of the apparatus, the heat of the heatsink being used to increase the rate at which oxygen is generated. A gas-permeable vent or other member is disposed over the mouth of the cavity to prevent the compound escaping.

Also envisaged is a method of oxygenating an LED lighting apparatus in accordance with the second aspect of the present invention, by allowing the chemical compound disposed within the body to react and release oxygen into the chamber. The method may comprise accelerating the reaction with a catalyst.

The method may comprise accelerating the reaction with heat or light energy.

Embodiments of the present invention will be described by way of examples only and with reference to the accompanying drawings, in which:

Figure 1 is a sectional view through an embodiment of LED lighting apparatus in accordance with the first aspect of the present invention;

Figure 2 is a sectional view through the distal end of a cable of an alternative embodiment of LED lighting apparatus in accordance with the first aspect present invention;

Figure 3 is a sectional view through an embodiment of LED lighting apparatus in accordance with the second aspect of the present invention; and

Figure 4 is a sectional view through an alternative embodiment of LED lighting apparatus in accordance with the second aspect of the present invention.

Referring to Figure 1 of the drawings there is shown an LED lighting apparatus comprising a sealed body 10) which defines a chamber 11) and an array of LED devices 13) disposed in the chamber 11) for emitting light through a translucent front wall 14) of the body 10). The array of LED devices 13) are controlled by a driver circuit 15) contained within a body 16) of encapsulation material. Each LED device 13) comprises a substrate of semiconductor material on which a dome-shaped lens of silicone is disposed. An elongate cable 17) extends from the rear of the body 10). The cable 17) comprises an outer sheath which contains a pair of elongate electrical conductors 18) that provide electrical power to the array of LED devices 13 via the driver circuit 15. A thin elongate tubular duct 19 co-extends with the pair of elongate electrical conductors 18 inside the sheath of the cable 17. The proximal end of the duct 19 opens into the chamber 11. The distal end of the duct 19 terminates at an over- molded formation 20 disposed intermediate opposite ends of the cable 17 where it is connected to the atmosphere via a vent 21 of semi-permeable material. The pair of elongate electrical conductors 18 extend beyond the formation 20 to a power supply or control unit (not shown) at the distal end of the cable 17. The sheath of the cable 17 may be omitted from the distal end portion of the cable 17. In use, when the LED devices 13 are illuminated, the apparatus heats up and the air inside the sealed chamber 11 expands and builds pressure. This build-up of pressure forces air along the duct 19 until it escapes to atmosphere through the vent 21 on the formation 20 until the pressure equalises.

When the LED devices 13 are extinguished, the apparatus cools and the air inside the sealed chamber 11 contracts and draws fresh oxygenated air along the duct 19 and into the chamber via the vent 21. In this manner, the oxygen is maintained at a sufficient level inside the chamber to prevent any degradation of the LED devices without compromising the sealing of the body against the ingress of the surrounding environment. Referring to Figure 2 of the drawings, in an alternative embodiment the distal end of the duct 19 terminates at an electrical connector 22 molded onto the distal end of the cable 17 where it is connected to the atmosphere via a vent 21 of semi-permeable material. The electrical connector is arranged to connect the distal end of the cable 17 to a power supply or control unit (not shown). Referring to Figure 3 of the drawings, there is shown an LED lighting apparatus which is similar in construction to the apparatus of Figure 1 and like parts are given like reference numerals. In this embodiment, the duct in the cable (not shown) is omitted. A gas permeable capsule 23 disposed within the chamber 11 contains a chemical compound and optionally a catalyst. The chemical compound may comprise hydrogen peroxide.

In use, the chemical compound slowly reacts and produces oxygen which is released through the gas permeable capsule 23 into the chamber 11 so as to increase the level of oxygen and thus prevent degradation of the light output by the LED devices 13 for the acceptable lifetime of the apparatus. Referring to Figure 4 of the drawings, in an alternative embodiment the chemical compound 24 is disposed in a cavity formed within a heatsink of the apparatus, the heat of the heatsink being used to increase the rate at which oxygen is generated. A gas-permeable vent 25 is disposed over the mouth of the cavity to prevent the compound 24 escaping but still allow the produced oxygen to dissipate into the sealed chamber.

LED lighting apparatus according to the present invention thus comprises a sealed body 10 which defines a chamber 11 in which LED devices 13 are disposed. Means are provided for increasing the oxygen level in the chamber 11 so as to prevent degradation of a silicone lens covering the LED of each device 13. In the first aspect of the invention, the means comprises a duct 19 which extends along a cable 17 connected to the apparatus that allows oxygen to flow into the chamber 11 from a point remote the apparatus. In the second aspect of the invention, the means comprises a chemical compound which releases oxygen into the chamber 11 over the lifetime of the apparatus. LED lighting apparatus in accordance with the present invention provides a substantially extended lifetime compared with conventional known LED lighting apparatus without significantly increasing the cost or complexity of the apparatus.