Led system for producing light
The invention relates to a system comprising a plurality of light emitting diodes, LEDs. The LEDs may be controlled in various in various manners in order to obtain any of one or more objects of the system. Thus, LEDs may be controlled for by controlling at least two of the following parameters: the luminous intensity of each of the LEDs, the luminous flux of each of the LEDs, the colour spectrum of the light being emitted from each of the LEDs, the spatial radiation pattern of the light being emitted from each of the LEDs, the spatial radiation pattern of the system, the junction temperature of each of the LEDs, the temperature of the surroundings to the LED, the amperage of the electrical power being supplied each or sections of the LEDs, the voltage of the electrical power being applied the LEDs and pulsing applied to the electrical power being applied each or sections of the LEDs.
The present invention relates to a system of light-emitting diodes (LEDs) for producing light. By the use of different control strategies the the luminous intensity and the luminous flux of the light produced may be controlled.
BACKGROUND OF THE INVENTIONU.S. Pat. No. 6,234,645 describes a system comprising at least four light-emitting diodes for the production of white light. The colour rendering index is above 60 and the luminous efficacy is preferably above 30 lm/W. In one embodiment, the colour temperature of the light can be adjusted by selectively switching the light-emitting diodes.
U.S. Pat. No. 5,783,909 describes a system for maintaining the luminous intensity of the light from at least one light-emitting diode. The system comprises a power supply electrically connected to the light-emitting diode for supplying pulses of electrical energy to this light-emitting diode. By adjusting the electrical energy supplied the luminous intensity of the light-emitting diode can be maintained at a pre-selected level, thereby compensating for the diminution of the output due to e.g. temperature variations or ageing.
U.S. Pat. No. 6,012,291 describes a system for temperature control of an optical semiconductor device, e.g. a light-emitting diode. By attaching the semiconductor device to a thermal conductor the temperature of this optical semiconductor device is kept at a constant temperature level despite any influence of the ambient temperature, heat sources etc.
GB 2 369 730 describes an LED control system for driving a current circuit for energising one or more LEDs. The system comprises a control system including a microprocessor arranged to control a pulse amplitude modulated (PAM) voltage controlled current circuit. The system may include a cooling fan for providing an airflow over the LEDs to reduce the ambient temperature at the LEDs. Reduction of the ambient temperature enables the microprocessor to increase the intensity light output by controlling the current circuit.
SUMMARY OF THE INVENTIONIt is an object of the present invention to provide a system capable of controlling the light emitting diodes (LED) and thus of the light being emitted from such a system, and which control enables adjustment of more than just one parameter in order to optimise the ratio between the luminous flux of the system and the electrical effect applied to the system. It is also an object of the present invention to provide an apparatus for emitting light by using LEDs, and where the lifetime of the LEDs and the luminous intensity, the luminous flux and the optical efficiency may be increased.
This object may be obtained by a method comprising controlling at least-all of the following parameters: the temperature of the surroundings of each of the LEDs, the luminous flux of each of the LEDs, and the electrical power being supplied to each of the LEDs, and where controlling the surrounding temperature establishes a means for controlling the luminous intensity being emitted from the system, and thus controlling the luminous flux of the LEDs, and establishes a means for not decreasing the lifetime of the LEDs, when the current of the electrical power is not increased during the lifetime of the LEDs.
The object may be obtained by a system comprising a plurality of LEDs for producing light, wherein each or sections of the LEDs are capable of emitting light at different wavelengths and said system further comprising means for controlling the luminous flux of each or sections of the LEDs separately, and said system further comprising means for controlling the luminous flux of the overall system comprising a plurality of LEDs by means of both controlling the surrounding temperature, either of each of the LEDs or commonly of all of the LEDs, and by means of controlling the electrical power being supplied to each of the LEDs, and where the means for controlling the electrical power consists in not increasing the current during the lifetime of the LEDs for thereby not decreasing the lifetime of the LEDs.
The object of the invention may also be obtained by a system comprising means for measuring the luminous intensity of light being emitted from the system, and said system further comprising means for controlling the surrounding temperature of each or of sections of the LEDs separately.
The object of the invention may even also be obtained by a system comprising means for controlling the junction temperature of each of the LEDs separately, and said system further comprising means for controlling the surrounding temperature of the LEDs.
The object of the invention may even also be obtained by a system comprising means for measuring the surrounding temperature of said LEDs, and said system further comprising means for controlling the surrounding temperature of said LEDs.
The object of the invention may even also be obtained by a system comprising means for measuring the electrical power applied LEDs, and said system further comprising means for controlling the surrounding temperature of said LEDs.
The object of the invention may even also be obtained by a system comprising means for measuring the electrical power applied LEDs, and said system further comprising means for controlling the electrical power applied to said LEDs.
A system according to the invention may comprise one or more of the following elements: control means for controlling the luminous intensity of the LEDs, control means for controlling the surrounding temperature of each of the LEDs and control means for controlling the pulse of the electrical power being supplied to each of the LEDs.
Controlling the luminous intensity of each or of sections of the LEDs establishes a means for controlling the dominants of one or more wavelengths in a colour spectrum in question in relation to more or less complementary colours to the colour or colour spectrum in question. The luminous intensity is preferably controlled by controlling each of or sections of LEDs.
Controlling the surrounding temperature, either of each of the LEDs or commonly of all of the LEDs, establishes a means for controlling the luminous intensity being emitted from the system, i.e. controlling the luminous flux of each or of sections of the LEDs. Controlling the luminous flux of each of the LEDs, establishes a means for controlling the capacity of light being emitted from the system. When controlling the surrounding temperature of the LED the lifetime and the optical efficiency may be increased.
Controlling the electrical power being supplied to each of the LEDs establishes a means for controlling the lifetime and optical efficiency and furthermore preventing thermal runaway of the LEDs, i.e. controlling the duration of LEDs given certain criteria such as colour spectrum and luminous intensity being emitted by each or sections of the LEDs. The electrical power is either controlled by controlling amperage or voltage of the electrical power, and/or by controlling the pulse of the electrical power, i.e. the duty factor of the electrical power.
BRIEF DESCRIPTION OF THE DRAWINGSThe invention will now be described with reference to the accompanying drawing, where
An array 4 of LEDs 5 is provided at the right side of the housing. Also, a cooling element 6 is provided centrally in the insulation 3 with a cool side of the cooling element 6 having contact to the gas contained within the interior of the insulation. Light emitted from the LEDs is directed from the array to the left and towards a central line A of the housing. In a focal point 7 of the light emitted from the LEDs, a reflector 8 such as a mirror is provided. The light emitted from the LEDs is directed along the central line A of the housing through a central hole 9 in the array 4, through a hole 10 in the insulation 3 and through a lens 11 in the housing 1 and out of the housing. In the embodiment shown, the lens 11 is a divergent concave lens. However, the lens could also be a convex lens for collecting the light, if the light after having been reflected by the reflector is not precisely focused by the reflector. Apart from the elements mentioned, also a thermal element (see
In
Also, in an alternative and preferred embodiment, the reflector is slightly curved with a concavity directed towards a focal point of the reflector. Although the intention is that the LEDs all are directed towards the focal point, then it must be remembered that the LEDs emit light along a certain angular extension, perhaps 12° as shown in
Preferably, both the array of LEDs and the reflector are curved as explained above so that a synergetic effect is obtained: Both the effect of the LEDs being directed towards the focal point of the reflector without having to bend the legs of the LEDs, and the effect of the reflector collecting the light being emitted from the LEDs before transmitting the light to the lens and through the lens.
Apart from the elements shown, the apparatus is preferably also provided with means (not shown) for establishing a vacuum inside the housing. The means for establishing the vacuum may be any exteriorly applied means capable of establishing a vacuum sufficient to provide a vacuum of a certain chosen magnitude depending on the application and use of the apparatus.
Also, one or more cooling elements, e.g. Pettier elements 3, are provided centrally on the other side of the LED mounting plate with a cold side of the cooling devices being in thermal contact with the mounting plate, and a hot side of the cooling devices being in thermal contact with the heat sink 2. Light emitted from the LEDs is directed through optics 8. Said optics is dependent on the LEDs viewing angle and/or the total spatial radiation pattern. One or more optical detectors can be placed near or in the visual vicinty of the light being emitted from LEDs, e.g. inside or outside the housing.
Insulation 7 may be provided within the housing and is intended for preventing heat transfer from the ambient surroundings and into the interior of the housing. The insulation may be any kind of insulation suited for the purpose, depending on the application and use of the apparatus and depending on the outer surroundings of the housing in relation of a temperature difference between the ambient temperature and the temperature in the interior of the housing. In order of minimising the power used in the cooling system a specially chosen gas and/or perhaps a vacuum may be established within the housing.
In
In the following, the interaction between the different elements will be described.
The electrical and electronic element 6 is intended for controlling the LEDs. Control of the LEDs comprises control of the electrical current applied to the LEDs, control of which LEDs that are to be lit, control of at which moment of time each of the LEDs is to be lit and control of which periods of time each of the LEDs is to be lit. Possibly, the control of the period of time which each of the LEDs is lit may be established by a constant current or by pulsation applied to the LEDs.
The luminous intensity is decreasing during the lifetime of the LEDs, and by controlling the luminous intensity of the LEDs, a constant luminous intensity during the lifetime can be obtained. By controlling the luminous intensity from each or sections of LEDs, a constant colour spectrum can also be obtained.
The electrical and electronic element is also intended for controlling the inner temperature of the housing by controlling the cooling device. By decreasing the junction temperature of the LED the optical efficiency will be increased and the lifetime prolonged. The limit of the temperature inside the housing is depending of the temperature limits of the LEDs according to the specification.
The electrical and electronic element 6 is also intended for controlling the cooling system by controlling the Peltier elements. Control of the Peltier elements comprises control of the electrical current and voltage applied the Peltier elements, control of at which periods of time Peltier elements are to be more or less active. Possibly, the control of the period of time each of the Peltier elements are active may be established by variable DC.
The reflectors are also controlled by the electrical and electronic element 6. By controlling each or sections of the reflectors and/or using optics, the emitting light from the LEDs can be directed in a desired or needed direction. The spectral radiation pattern can be symmetric or asymmetric, depending on the application and use of the apparatus.
The resistor, which constitutes part of the LED (see
The insulation is intended for insulating the gas within the insulation towards any heat, transfer from the outside surroundings of the housing. The insulation may be any kind of insulation suited for the purpose, depending on the application and use of the apparatus and depending on the outer surroundings of the housing. Thus, the insulation may be polystyrene, it may be any insulation material such as the commonly known insulation woollen materials based on rock or based on glass, it may be other materials suited for insulation purposes and capable of assisting in a maintaining of a certain temperature within the insulation in the housing despite the risk or possibility of possible heat transfer from the outer surroundings of the housing due to a temperature difference.
The cooling element, in the embodiment shown the Peltier-element, is, as mentioned, intended for cooling the gas within the insulation of the housing. Cooling of the gas may take place by cooling the gas to a constant or variable temperature depending on the application and use of the system.
The possible means for establishing the vacuum is intended for subjecting the gas contained within the insulation to vacuum or perhaps subjecting the gas contained within the entire housing to vacuum.
Thus, if the volume of the housing or the volume within the insulation is constant, then, if the pressure is decreased by the exteriorly applied vacuum means, then the amount of moles is decreased correspondingly. However, an advantage may be obtained, when initially subjecting the gas to a vacuum. If the temperature inside the housing, after having been subjected to a vacuum, is decreased, then the amount of moles to be cooled is much less, and thus the amount of energy for cooling the gas contained within the insulation is decreased accordingly.
Given a desire or a need to decrease the temperature to a certain low level, then the amount of electrical energy to be used for driving the Peltier-element may be less than if the gas contained within the insulation is not subjected to vacuum initial to cooling the gas. Alternatively, given a certain amount of electrical energy available to drive the Peltier-element, then the low temperature, which it may be desirable of needed to reach, may be lower than if the gas is not subjected to vacuum initially to cooling the gas.
However, depending on the low temperature, which it is desirable or needed to be reach, then the initial subjection of vacuum to the gas contained within the insulation may be suspended with. This may be the case, if the gas contained within the insulation has a low specific heat, or if the temperature of the atmosphere surrounding the housing is sufficiently low, perhaps during a winter season, compared to the temperature needed.
Other ways of controlling the LEDs will hereafter be described. The LEDs may be subjected to an on/off pulsation in order to increase the luminous intensity of the light being emitted. This pulsation may preferably be effected as a square wave pulsation, where a certain current is applied to individually chosen LEDs of the array of LEDs, where said current is maintained at a certain level for a certain amount of time, and where the current is cut off subsequent to the certain amount of time, thereby resulting in an extinguishing of the LED. However, other waveforms such as a sinusodially shaped waveform or other waveforms such as a triangularly shaped waveform may be applied in stead of a square waveform.
Most preferred, the square wave pulsation is applied so that an overlap between applied currents to the individual LEDs is obtained. Thus, just before the applied current at a certain level is cut off for one LED, then the next LED to be subjected to the current is being applied the current. Thus, an overlap is established between the cut-off of the current of one LED and the application of current to another LED. This overlap reduces the risk of the total array of LEDs emitting a flickering light. This could however be the case due to a possible delay between the cut-off of current to one LED, thereby extinguishing the LED, and before another LED is applied current for that other LED to emit light corresponding to the light just having been emitted previously by the one LED.
Increasing the current during the lifetime of the LEDs may decrease the lifetime of the LEDs compared to not increasing the current during their lifetime, because of the fact that the lifetime of the LEDs also depends on the level of current applied to the LEDs. Thus, if the current is constantly increased, the lifetime of the LEDs will be reduced. Alternatively to maintaining a luminous intensity of 100% during the entire lifetime of the LEDs, a lower luminous intensity may be the limit desirable to maintain, however, the limit still being greater than the limit possible to obtain, if the current applied is not increased during the lifetime of the LEDs.
The system may be used in many applications for many different uses. Major application may be outdoor lighting, show-lights and central domestic or office lighting, where a number of centrally installed systems according to the invention is used to supply light to a plurality of locations by transmitting the light along fibre-optical cables.
Claims
1. A method for controlling light being emitted from a light-emitting system comprising a plurality of light emitting diodes, LEDs, said method comprising controlling at least all of the following parameters: the temperature of the surroundings of each of the LEDs, the luminous flux of each of the LEDs, and the electrical power being supplied to each of the LEDs, and where controlling the surrounding temperature establishes a means for controlling the luminous intensity being emitted from the system, and thus controlling the luminous flux of the LEDs, and establishes a means for not decreasing the lifetime of the LEDs by the current of the electrical power not being increased during the lifetime of the LEDs.
2. A system comprising a plurality of LEDs for producing light, wherein each or sections of the LEDs are capable of emitting light at different wavelengths and said system further comprising means for controlling the luminous flux of each or sections of the LEDs separately, and said system further comprising means for controlling the luminous flux of the overall system comprising a plurality of LEDs by means of both controlling the surrounding temperature, either of each of the LEDs or commonly of all of the LEDs, and by means of controlling the electrical power being supplied to each of the LEDs, and where the means for controlling the electrical power consists in not increasing the current during the lifetime of the LEDs for thereby not decreasing the lifetime of the LEDs.
3. An LED system according to claim 2, where each of the diodes are capable of emitting light at different wavelengths, the wavelengths being: a first wavelength in the range of visible blue light, preferably in the range of 430 nm to 490 nm, a second wavelength in the range of visible green light, preferably in the range of 530 nm to 565 nm, and a third wavelength in the range of visible red light, preferably in the range of 605 nm to 630 nm.
4. An LED system according to claim 2, wherein the controlling means is a power supply, and wherein luminous intensity of the system is controlled by said power supply by adjusting the one or more of the parameters amperage, voltage or duty factor of the electrical power supplied.
5. An LED system according to claim 2, wherein the controlling means is a power supply, and wherein luminous intensity of the system is controlled by said power supply by introducing a pulse width from the electrical power supplied to the LEDs.
6. An LED system according to claim 2 and comprising a plurality of LEDs for producing light, wherein each or sections of the LEDs are capable of emitting light at different wavelengths and said system comprising means for measuring the junction temperature of said LEDs, and said system further comprising means for controlling the junction temperature of said LEDs and wherein said measuring means is adapted for sending a temperature signal to temperature controlling means, said signal intended for being used in the control of the surrounding temperature of each or sections of the LEDs separately, and wherein the temperature controlling means is capable also of controlling the junction temperature of the LEDs.
7. An LED system according to claim 6, where each of the diodes are capable of emitting light at different wavelengths, the wavelengths being: a first wavelength in the range of visible blue light, preferably in the range of 430 nm to 490 nm, a second wavelength in the range of visible green light, preferably in the range of 530 nm to 565 nm, and a third wavelength in the range of visible red light, preferably in the range of 605 nm to 630 nm.
8. An LED system according to claim 2 and comprising a plurality of LEDs for producing light, wherein each or sections of the LEDs are capable of emitting light at different wavelengths and said system comprising means for measuring the electrical power applied to the LEDs, and said system further comprising means for controlling the electrical power applied to said LEDs and wherein the electrical power applying means is capable of controlling the applying a current as a square wave current, preferably a square wave current establishing overlap between a current being applied initially to one LED and a current being applied subsequently to another LED.
9. An LED system according to claim 8, where each of the diodes are capable of emitting light at different wavelengths, the wavelengths being: a first wavelength in the range of visible blue light, preferably in the range of 430 nm to 490 nm, a second wavelength in the range of visible green light, preferably in the range of 530 nm to 565 nm, and a third wavelength in the range of visible red light, preferably in the range of 605 nsm to 630 nm.
10. An LED system according to claim 2, wherein said system comprises a cooling element for controlling the temperature of the surroundings of the plurality of LEDs.
11. An LED system according to claim 10, where a cool side of the element is facing an interior of a housing containing the LEDs, and where a hot side of the element is facing exterior surroundings of the housing.
12. An LED system according to claim 10, where the cooling element at a hot side of the element is provided with heat transfer means such as ribs in order to increase the heat transfer between the element and surroundings of the hot side.
13. An LED system according to claim 10, where the cooling element is chosen among on the following elements: a Peltier element, a heat exchanger of a compressed gas cooling system, and a flow of fluid, i.e. a gas or a liquid.
14. An LED system according to claim 2, wherein said system comprises a vacuum unit for controlling the gas pressure within a housing containing the plurality of LEDs.
15. An LED system according to claim 2, wherein said system comprises a gas unit for controlling the amount of gas contained within a housing containing the plurality of LEDs.
16. An LED system according to claim 2, wherein said system comprises a gas unit for controlling the composition of the gas contained within the housing containing the plurality of LEDs.
17-57. (canceled)
Type: Application
Filed: Sep 16, 2003
Publication Date: May 25, 2006
Applicant: First Flower & Fruit Company A/S (Pandrup)
Inventor: Palle Stevn (Aalborg SV)
Application Number: 10/528,023
International Classification: H01J 7/24 (20060101);