Patent Description:
Among solution to recreate artificially sunlight, Xenon light sources or other artificial light sources are largely used as the light source of a standard solar simulator. Among others a xenon arc lamp is quite expensive and provides a high flux which is not required for most applications. Mercury xenon lamps used to be another kind widely used light source in the early space solar simulators. However, mercury arc lamps have narrow bands of energy emission. <CIT> presents a solution according to which the solar simulator combines mercury lamps and halogen lamps, some of the halogen lamps being provided further with a filter for limiting the amount of emitted infra-red light of these halogen lamps and mercury lamps to compensate the weak radiation of the halogen lamp in the shorter wavelengths (blue and UV portion). <CIT> presents a solar simulator comprising a high-intensity discharge (HID) lamp type and a halogen lamp type, which lamps are applied simultaneously and are provided with infrared filter means to provide a mixture of light approximating radiated sunlight.

Light-emitting diode lamp (LED) is a semiconductor light source based on the electroluminescence phenomenon, which emits a narrow-spectrum light when electrically biased in the forward direction of the p-n junction. The advantages of LEDs brought them to be recently the right source of light for solar simulators: among others, they have very long lifetime up to <NUM>,<NUM> to <NUM>,<NUM> hours, they can be controlled very fast within microseconds, they have a relatively narrow monochromatic output spectrum (except white LEDs) and are available in a wide variety of colors and wavelengths, which means combining a number of required colors LEDs can close-match application spectrum, and they are compact with low energy consumption.

For example, in <CIT> is presented a LED solar simulator optical system using LEDs with various peak wavelengths within the wave band of <NUM>-<NUM>. All LEDs with the same peak wavelength are integrated into a module with a lens. Also, in <CIT> the LED-based simulator light source uses at least one diffractive element to spectrally combine the discreet spectral outputs of the individual LED groups to form a broad spectral output at the work surface. <CIT> and <CIT> also propose solar simulators containing only LED light sources.

These and other LED based solar simulators provides simulators that needs to fulfil international standards relative to the solar simulator performance requirements, including IEC60904-<NUM> Ed2 or Ed3 which specify how the spectrum of the solar simulator should extend up to <NUM>. In that condition, providing a solar simulator with LEDs that can provide light for wavelengths above <NUM> is not a reliable technology and is moreover very expensive. More specifically, above <NUM>, the use of two LEDs is common, notably having their respective peak wavelength value at <NUM> and <NUM>, both of which are very expensive.

Also, there exists halogen based solar simulators, where LEDs are used to complete spectrum below ~<NUM>. However, they are prone to stability, heat and light source life time issues inerrant to the use of halogen providing more than <NUM>% of the total irradiance of the solar simulator. Actually, it is important to have a relative stable temperature of the solar panel illuminated by the solar simulator in order to get a correct measurement of the performance of the solar panel. With halogen based solar simulators, the halogen lamp(s) take(s) time for the filament to heat-up and stabilize, about <NUM>-<NUM> seconds, so that the real irradiation time is up to a few seconds during which light is emitted which radiates the solar panel which produces heat. This radiation duration of the halogen lamp is therefore far longer than the measurement time which is only a few hundreds milliseconds (solar simulator usually use pulsed light or flash of about <NUM> milliseconds up to <NUM> milliseconds). In <CIT>, a sunlight simulator is described, where an array composite light source has an irradiation area of output light that can reach more than <NUM> to <NUM> range. To that end, the array composite light source comprises a white light LED, a R/G LED, a ultraviolet LED and infrared halogen tungsten lamp.

There is a need to provide solar simulators that can cover the solar spectrum including the wavelength range beyond <NUM> and at least up to <NUM>, which is less costly than the <NUM>% LEDs solution.

This is also an aim of the present invention to provide a solution for a solar simulator that does not generate too much heat in the solar panel which is illuminated by the solar simulator, notably in the IR wavelength range.

This is also an aim of the present invention to provide an improved solar simulator that would overcome drawbacks of the existing and prior art solutions.

According to the invention, these aims are achieved by means of a solar simulator comprising an array of light sources including LED light sources and at least one non-LED light source, wherein:.

With such a solution, is provided a solar simulator that is less expensive since avoiding the use of only LED light sources for the infrared-light wavelength range. Also using non-LED light source(s) within at least a portion of the infrared-light wavelength range covered by said solar simulator provides a lower total irradiated power for the solar simulator, thereby less heat generated in the solar panel and thereby a lower need for cooling, which is less expensive and more reliable along the life time of the solar simulator.

In the present text, the words "irradiance" or "irradiation" correspond both to the same parameter which is the irradiated power by the light source to a target plane, which SI unit is W/m<NUM>.

In one embodiment, more than <NUM>% of the irradiance provided by the solar simulator is provided by the LED light sources. Also, in some embodiment, more than <NUM>%, and possibly more than <NUM>%, and eventually about <NUM>% of the irradiance provided by the solar simulator is provided by the LED light sources.

According to the invention, the solar simulator comprises further a filtering device placed above the non-LED light source with respect to the irradiation direction of the solar simulator, said filtering device reducing the total irradiance provided said by non-LED light source. With the use of such a filtering device, it is possible to keep within the wavelength range radiation emission spectrum of the solar simulator enough irradiance to match as close as possible the irradiance of sunlight and to eliminate extra irradiance, avoiding therefore too much heat generation in the solar panel or any other object illuminated by the solar simulator.

In one embodiment, said filtering device reduces the wavelength range radiation emission spectrum of the non-LED light source. With the use of such a filtering device, it is possible to keep within the wavelength range radiation emission spectrum of the solar simulator one wavelength sub-range (sub-interval) or several wavelength sub-ranges (sub-intervals) provided by the filtered light of the non-LED light source, while eliminating part of or totally one wavelength sub-range (sub-interval) or several wavelength sub-ranges (sub-intervals) provided by the non-filtered light of the non-LED light source. For instance the eliminated (filtered) wavelength sub-range(s) do not belong to the solar light spectrum or the eliminated (filtered) wavelength sub-range(s) belongs to the solar light spectrum but is (are) provided in a convenient way be the LED light sources.

According to the invention, said filtering device comprises an optical high-pass filter or an optical band pass filter. As a possibility, the filtering device comprises only one optical high-pass filter or one optical band pass filter. As another possibility, said filtering device comprises one optical high-pass filter or one optical band pass filter, and another type of filter (one filter or several filters, said filters belonging to same type of filters or different type of filters).

In one embodiment, said portion of the infrared-light wavelength range covered only by said non-LED light source covers, namely overlap, at least the <NUM>-<NUM> wavelength range. As LED light sources having peak wavelength over <NUM>, notably within the <NUM>-<NUM> wavelength range are expensive light sources, this allow to replace LED light sources for at least, including exactly, the <NUM>-<NUM> wavelength range by at least one non-LED light source.

In one embodiment, said non-LED light source is an halogen light source, said halogen light source being preferably a tungsten halogen lamp or comprising tungsten halogen lamps. Such an halogen light source provides a convenient complementary light source to the LED light sources, in particular when providing a limited irradiation, including but non-limited to wavelength range above <NUM>, <NUM> or <NUM>.

In one embodiment, said solar simulator is a pulsed solar simulator. In a possible embodiment, the pulses of said solar simulator are equal or longer than <NUM>. In another embodiment, said simulator is a continuous solar simulator.

In one embodiment, in said solar simulator said filtering device reduces to less than <NUM>% of the total irradiance the irradiance provided by said non-LED light source for wavelengths equal or lower than <NUM>, or for wavelengths equal or lower than <NUM>, or for wavelengths equal or lower than <NUM>. Possibly, said filtering device reduces to less than <NUM>%, or to <NUM>% or to less than <NUM>% the irradiance provided by said non-LED light source for wavelengths equal or lower than <NUM>, or for wavelengths equal or lower than <NUM>, or for wavelengths equal or lower than <NUM>.

In one embodiment of said solar simulator, said filtering device reduces to less than <NUM>% the irradiance provided by said non-LED light source for wavelengths equal or larger than <NUM>, or for wavelengths equal or larger than <NUM>, or for wavelengths equal or larger than <NUM>. Possibly, said filtering device reduces to less than <NUM>% the irradiance provided by said non-LED light source for wavelengths equal or larger than <NUM>, or for wavelengths equal or larger than <NUM>, or for wavelengths equal or larger than <NUM>.

In one embodiment of said solar simulator, said portion covers a wavelength range including from <NUM> onwards.

In one embodiment, said solar simulator has a light spectrum wherein the visible wavelength range is covered only by LED light sources.

In one embodiment of the solar simulator, less than <NUM>% (possibly less than <NUM>% or less than <NUM>% of the total irradiance provided by said solar simulator is provided by said non-LED source.

In one embodiment of the solar simulator, less than <NUM>% of the total irradiance provided by said solar simulator is provided by said non-LED source. In parallel, in a possible embodiment, a maximum of about <NUM>%, or preferably of about <NUM>% of the total irradiance of the solar simulator is provided by said non-LED source.

In one embodiment, less than <NUM>% of the irradiance provided by said solar simulator within the wavelength range between <NUM> to <NUM> is provided by said non-LED light source.

In one embodiment of the solar simulator, less than <NUM>% of the irradiance provided by said solar simulator within the wavelength range between <NUM> to <NUM> is provided by said non-LED light source.

In one embodiment, the irradiance provided for wavelengths larger than1000 nm (or larger than <NUM>) is provided for more than <NUM>% by the non-LED light source.

In one embodiment of the solar simulator, the range of the wavelength spectrum of the solar simulator up to <NUM> is covered only by said LED light sources. According to a possibility, the range of the wavelength spectrum of the solar simulator up to at least <NUM> or also possibly up to at least <NUM> is covered only by said LED light sources.

In one embodiment of the solar simulator, the range of the wavelength spectrum of the solar simulator up to <NUM> is covered only by said LED light sources. In one embodiment, the range of the wavelength spectrum of the solar simulator up to <NUM> is covered for the most part only by said LED light sources. In that situation, it can be that between <NUM> and <NUM>, only a small range of the wavelength spectrum of the solar simulator uses LED light sources, for instance only above <NUM> or above <NUM> or above <NUM>. In one embodiment, in the range of the wavelength spectrum of the solar simulator up to <NUM>, at each wavelength value the irradiance provided by the LED light sources is larger than the irradiance provided by the non-LED light source.

In one embodiment of the solar simulator, the range of the wavelength spectrum of the solar simulator up to <NUM> is covered only by said LED light sources. In one embodiment, the range of the wavelength spectrum of the solar simulator up to <NUM> is covered for the most part only by said LED light sources.

In one embodiment of the solar simulator, at least one of said LED light sources has a peak wavelength equal or larger than <NUM>.

In one embodiment of the solar simulator, within the wavelength spectrum of the solar simulator, for the wavelength range up to <NUM>, more than <NUM>% of the total irradiance of the solar simulator is provided by the LED light sources. In one embodiment of the solar simulator, within the wavelength spectrum of the solar simulator, for the wavelength range up to <NUM>, more than <NUM>%, or possibly more than <NUM>%, of the total irradiance of the solar simulator is provided by the LED light sources.

In one embodiment of the solar simulator, within the wavelength spectrum of the solar simulator, for the <NUM> wavelength, more than <NUM>% of the total irradiance of the solar simulator is provided by the LED light sources. In one embodiment of the solar simulator, within the wavelength spectrum of the solar simulator, for the <NUM> wavelength, more than <NUM>% (or possibly more than <NUM>%) of the total irradiance of the solar simulator is provided by the LED light sources.

Further embodiments are described in the dependent claims and below.

The invention will be better understood with the aid of the description of embodiments given by way of example and illustrated by the figures, in which:.

According to the invention, the solar simulator <NUM> comprises an array of light sources including LED light sources and at least one non-LED light source.

In some embodiments, said LED light sources <NUM> are distributed on an active face <NUM> of at least one plate <NUM> forming for instance a PCB, namely a Printed circuit board. In <FIG> only one PCB plate <NUM> is shown but there could be two, three, or more (several or a plurality) plates <NUM>. This plate <NUM> or these plates <NUM> as/are mounted on a structure to form a(n array of) plate(s) parallel to the target plan <NUM> to be illuminated. Also, these plates are shown to be flat and forming a plane but other geometrical configurations could be used for the plate(s) <NUM>, including an curved 3D geometry, such as a portion of a sphere. In the case of planar plates <NUM> or PBC covered with LED light sources <NUM> on the active face <NUM>, the direction of irradiation or direction of emission of light (arrow L in <FIG>) is orthogonal with respect to the plate(s) <NUM> and directed from the active face <NUM> towards the target plane <NUM>. The target plan <NUM> to be illuminated is for instance formed by the outer face of a solar panel or a photovoltaic panel (not shown).

In a possible first embodiment shown in <FIG>, said PCB plate <NUM> comprises further an opening <NUM>, said non-LED light source <NUM> being placed behind said opening <NUM>. In the example shown, this opening <NUM> could be circular or with another shape such as a square, a rectangle, an oval shape or another shape.

As a possibility, the non-LED light source <NUM> is an halogen light source, said halogen light source being possibly a tungsten halogen lamp or comprising tungsten halogen lamps. As an example, this halogen lamp has the following features :
A tungsten filament sealed in a transparent envelope that is filled with a mixture of inert gas and a small amount of halogen, with connection pins.

According to this first embodiment of <FIG>, the solar simulator <NUM> further comprises a filtering device <NUM> formed by or comprising a filter. This filtering device <NUM> is used in combination with the non-LED light source <NUM>. In a variant, this is an optical band pass filter, limiting more than <NUM>% of the irradiance or even stopping <NUM>% of the light for the wavelength at least between <NUM> and <NUM>, possibly between <NUM> and <NUM>. As an example, this filter has the following features :.

This filtering device <NUM> is placed upstream the non-LED light source <NUM> and covers a surface large enough to have the whole light beam of the non-LED light source <NUM> to pass through the filtering device <NUM>. In <FIG> the filtering device <NUM> is placed on the opening <NUM> of the PCB plate <NUM>, more precisely on the face of the PCB plate not covered by the LED light sources <NUM>. In other possible (not shown) embodiments, the filtering device <NUM> is placed through the opening <NUM> of the PCB plate <NUM> or the filtering device <NUM> is placed on the opening <NUM> of the PCB plate <NUM> on the face of the PCB plate which is covered by the LED light sources <NUM>.

In the present text, "upstream" and "downstream" refer to the direction of the light of the solar simulator <NUM>, the L arrow showing the direction of irradiation of the solar simulator <NUM> in <FIG> being orientated from upstream to downstream.

According to this first embodiment of <FIG>, the solar simulator <NUM> further comprises a reflector <NUM> placed around and possibly upstream the non-LED light source <NUM>. As can be seen in <FIG>, this reflector <NUM> extends from behind the non-LED light source <NUM>, with respect to the plate <NUM> (or with respect to the filtering device <NUM> if present), and around the non-LED light source <NUM> up to a location downstream the non-LED light source <NUM>, notably up to the position of the filtering device <NUM> in case of presence of this filtering device, otherwise possibly up to the opening <NUM>, otherwise possibly up to the rear face of the PCB plate <NUM> (face which is opposite to the active face <NUM>).

This reflector <NUM> placed behind and around the non-LED light source <NUM> can reflect the portion of the light beam of the non-LED light source <NUM> which is not directed towards the opening <NUM>, downstream, i.e. towards and through the opening <NUM>. To that end, the reflector <NUM> has an internal surface with a high reflection coefficient and a low absorption coefficient, for instance a metallic internal surface forming thereby a mirror like surface.

As can be seen in <FIG>, a possible shape for the reflector <NUM> is a shape of revolution around an axis coaxial with the main direction of the non-LED light source <NUM>, with is limited by a curved line (generatrix). This possible shape is a corolla like shape or a cone, or a truncated cone with the larger diameter and aperture surrounding or facing the opening <NUM>.

So, in the configuration of <FIG>, from upstream to downstream, there is the reflector <NUM>, the light emitting portion of the non-LED light source <NUM>, the filtering device <NUM>, the PCB plate(s) <NUM> and the light emitting portion of the LED light sources <NUM>.

In a possible second embodiment shown in <FIG> and <FIG>, said non-LED light source <NUM> is placed on or above said active face <NUM> of the plate <NUM>, within a lamp housing <NUM>. This lamp housing <NUM> surrounds the non-LED light source <NUM>. This lamp housing <NUM> forms a wall surrounding the non-LED light source <NUM> and focuses the light beam of the non-LED light source <NUM> towards the target plane <NUM>, for instance this lamp housing <NUM> stops the external annular portion of the light beam of the non-LED light source <NUM>.

According to this second embodiment of <FIG> and <FIG>, the solar simulator <NUM> further comprises a filtering device <NUM> as previously described. This filtering device <NUM> is possibly placed on the top (upstream side) of the lamp housing <NUM>, forming thereby a closure of the lamp housing <NUM>. This filtering device <NUM> is placed above the non-LED light source <NUM> in the irradiation direction L of the solar simulator <NUM>.

In an embodiment, as shown in <FIG> illustrating a possible light spectrum obtained with a solar simulator according to the invention (with six LED light sources <NUM> and one non-LED light source14 associated with a filter), said LED light sources are divided into at least six different type of LEDS having different peak wavelength values. More precisely in <FIG>, showing the light spectrum (spectral irradiance in arbitrary units - A. -that can be W. nm-<NUM> in ordinate and wavelength in nanometers in abscissa), the solar simulator uses in this case exactly six different type of LEDS having different peak wavelength values, notably a peak wavelength value between <NUM> and <NUM> (for instance a peak wavelength value of <NUM> as shown in <FIG>), a peak wavelength value between <NUM> and <NUM> (for instance a peak wavelength value of <NUM> as shown in <FIG>), a peak wavelength value between <NUM> and <NUM> (for instance a peak wavelength value of <NUM> as shown in <FIG>), a peak wavelength value between <NUM> and <NUM> (for instance a peak wavelength value of <NUM> as shown in <FIG>), a peak wavelength value between <NUM> and <NUM> (for instance a peak wavelength value of <NUM> as shown in <FIG>) and a peak wavelength value between <NUM> and <NUM> (for instance a peak wavelength value of <NUM> as shown in <FIG>).

More generally, said LED light sources <NUM> have peak wavelength values between <NUM> and <NUM>, or said LED light sources <NUM> cover at least the wavelength range between <NUM> and <NUM>.

In an embodiment, said LED light sources <NUM> are divided into at least ten different type of LED light sources <NUM> having different peak wavelength values, possibly nineteen different type of LED light sources <NUM>.

In an embodiment, as shown in <FIG>, said non-LED light source <NUM> has a light spectrum (which is illustrated after filtration through the filtering device <NUM>) extending at least between <NUM> and <NUM>, and notably at least from <NUM> and <NUM>.

Above <NUM>, the spectrum of the solar simulator <NUM> can have several possible configurations, including no irradiance or low irradiance, but preferably has a spectral irradiance in line with or close to the spectral irradiance of the solar light spectrum.

To complete the solar simulator other conventional equipments can be used, among others possible equipments are as follows : a cooling system with air conditioner or any other type of cooling distribution, capacitor bank, electrical panels, computer, display, thermal chamber, temperature sensors, power supply, electronic load.

Also, in a possible embodiment, taken alone or in combination with the previously described embodiments or variants, the solar simulator further comprises a diffuser, notably an optical diffuser, which is placed on the light path to homogenize the angular response of the light sources.

Also, in a possible embodiment, taken alone or in combination with the previously described embodiments or variants, the solar simulator further comprises a reflector, notably an assembly optionally coated with reflective material, which is placed in regard of the light source in order to reorientate the maximum of the light emitted by the non-LED light source in the direction of the target plane.

Also, in a possible embodiment, taken alone or in combination with the previously described embodiments or variants, the solar simulator further comprises optical lens(es), notably fly-eye, convex or other type of lenses, which is (are) placed on the light path between the non-LED light source <NUM> or non-LED light sources.

In the case of use of the combination of a reflector, diffusor and optical lens(es), this provides a solution to homogenize the angular irradiation of the non-LED light source(s) <NUM> and also to improve light uniformity on the target plane <NUM>.

With the solar simulator of the present invention including a filtering device, the applicant performed to reduce about <NUM> times, from <NUM>% to about10%, the impact of the solar panel heating problem by filtering the light of the halogen light source.

Claim 1:
Solar simulator (<NUM>) comprising an array of light sources including LED light sources (<NUM>) and at least one non-LED light source (<NUM>), wherein:
- at least a portion of the infrared-light wavelength range covered by said solar simulator (<NUM>) is covered only by said non-LED light source (<NUM>), and characterized in that
- more than <NUM>% of the irradiance provided by the solar simulator (<NUM>) is provided by the LED light sources (<NUM>),
- said solar simulator (<NUM>) comprises further a filtering device (<NUM>) placed above the non-LED light source (<NUM>) with respect to the irradiation direction of the solar simulator (<NUM>), said filtering device (<NUM>) reducing the total irradiance provided by said non-LED light source (<NUM>); and
said filtering device (<NUM>) comprises an optical high-pass filter or an optical band pass filter.