Patent Application
20160327212
1. Field of the Invention
Conventional incandescent light sources generally provide radial distribution of light which is used to illuminate a room or the like. However, incandescent light sources consume a lot of power. Replacing incandescent light sources with light emitting diode (LED) light sources improves the power efficiency considerably. Unfortunately, most LEDs emit light into a hemisphere, whereas incandescent light sources are able to provide substantially uniform light emission into an entire sphere. As a result, the mere replacement of incandescent light sources by LED light sources often leads to unsatisfactory and/or insufficient illumination of a space, such as a room.
In addition, conventional incandescent light sources generate a broad spectrum that is experienced as warm white light. LEDs do not generate white lights by themselves. White light may be obtained by using LEDs emitting a short wavelength, e.g. a wavelength between about 420-470 nm, covered with phosphorous material which converts a portion of the emitted light into light having a longer wavelength. The white light produced in this way is often experienced as “cold”. Alternatively, white light may be obtained by using different types of LEDs, each type being suitable for the emission of a wavelength in a different wavelength region. For example, LEDs arranged for emitting blue light may be combined with one or more LEDs arranged for emitting green light and red light. By specific arrangements and the use of optical elements to obtain color mixing white light may be formed. However, it is very difficult to obtain a rather uniform emission of white light over a large solid angle.
Generally, the differences between incandescent light sources and light sources using LEDs described become more noticeable when pluralities LEDs are used in LED light sources. It is extremely difficult to realize a light source using a plurality of LEDs that may act as a point source, particularly if such behavior should coincide with sufficient color mixing.
The object of the invention is to provide a light source using LEDs which provide improved illumination over a large solid angle in a rather uniform way. For this purpose, an embodiment of the invention provides a light source comprising: a light unit comprising a plurality of light emitting diodes distributed in the form of a spatial arrangement having a center position, wherein the plurality of light emitting diodes includes at least two different types of diodes, each type of diode being arranged for the emission of radiation within a different wavelength range; and a hollow curved cap covering the light unit, the cap being substantially transparent for radiation emitted by the light unit and being provided with an axially symmetric depression forming a protrusion in the interior of the cap, wherein the symmetry axis of the depression substantially coincides with the center position of the spatial arrangement of the plurality of light emitting diodes. The use of this light source provides a rather uniform emission of light over a large solid angle while benefiting from the power efficiency of LEDs.
Embodiments of the invention further relate to a lamp comprising a light source as mentioned above and a hollow enclosure at least partially enclosing the optical element, wherein at least a portion of the enclosure is transparent for radiation emitted by the optical element.
Embodiments of the invention further relate to a light assembly comprising: a light source as mentioned above; and a luminaire for accommodating the light source; wherein the radius of a virtual hemisphere tangent to the light source is at least 10 times smaller than the radius of a virtual hemisphere tangent to the luminaire. Such light assembly may not only be able to provide improved illumination over a large solid angle in a rather uniform way, but may also enable the light source to be used as a point source. This may even be the case for a light source using a plurality of LEDs.
Finally, embodiments of the invention relate to a method of manufacturing a light source comprising: forming a light unit by distributing a plurality of light emitting diodes in the form of a spatial arrangement having a center position, the plurality of light emitting diodes including at least two different types of diodes, each type of diode being arranged for the emission of radiation within a different wavelength range; molding a hollow curved cap being substantially transparent for radiation emitted by the light unit, the cap being provided with an axially symmetric depression forming a protrusion in the interior of the cap; and placing the cap over the light unit so as to cover it, wherein the placement is such that the symmetry axis of the depression substantially coincides with the center position of the spatial arrangement of the plurality of light emitting diodes.
Various aspects of the invention will be further explained with reference to embodiments shown in the drawings wherein:
The following is a description of various embodiments of the invention, given by way of example only and with reference to the drawings.
The LEDs 3 are distributed in the form of a spatial arrangement. The choice of a specific arrangement may be based on the desired purpose. Two examples of spatial arrangements are given in
The cap 20 is a hollow curved cap and covers the light unit 10. The cap 20 is substantially transparent for radiation emitted by the light unit 10. The cap is provided with an axially symmetric protrusion 22 in the interior of the cap 20. The protrusion forms a depression 21 in the exterior of the cap 20. The symmetry axis of the protrusion 21 substantially coincides with the center position of the spatial arrangement of the plurality of LEDs 3. The alignment of the protrusion 22 with the LEDs 3 enables increased mixing of light emitted by the different types of LEDs 3. As a result, improved color mixing can be achieved.
Furthermore, the use of the hollow cap 20 with the protrusion 22, and resulting depression 21, enables the light source 1 to emit light in a substantially uniform fashion over a solid angle that exceeds the solid angle of the light emitting diodes. Due to the alignment of the symmetry axis of the protrusion 22 with the center position of the spatial arrangement of the plurality of light emitting diodes 3 the solid angle of the light source 1 may approximate the solid angle of a point source.
In
In
Some embodiments of the inventions are particularly useful for the generation of white light by mixing the spectra of two or more different types of LEDs. For example, one of the LED types 3a, 3b being used may correspond to an LED provided with a layer comprising a phosphorous compound. The phosphorous compound is arranged to convert at least a portion of the radiation emitted by the LED into radiation having a different, generally a longer, wavelength. In such case, this type of diode may be a so-called “white LED”, i.e. an LED which produces white light by mixing the light emitted by the LED with light converted by the phosphorous layer. Typically a white LED uses an LED arranged for emitting wavelengths in a range of about 420-470 nm. The light emitted by “white LEDs” generally have a low color rendering index, i.e. the emitted light is perceived as being “cold” light. The use of diodes emitting wavelengths in a range of about 590-670 nm, i.e. red LEDs, can improve the perception of the light emitted by the light source.
The protrusion 22 is preferably cone-shaped. The use of a cone-shaped protrusion 22 improves uniform transmission over a large solid angle. Light emitted from the LEDs is more likely to reflect on the inner surface of the cap, which provides a better angular dispersion of light. Additionally, the increased light dispersion results in improved color mixing which improves the uniformity of the light being emitted by the light source. A further improvement of light dispersion and color mixing can be achieved by shaping the protrusion 22 such that a top portion of the protrusion has a convex surface shape if observed from the direction of the light unit 10. In other words, in this embodiment, the top portion of the protrusion 22 has a convex outer surface shape.
At least a portion of the inner surface of the cap 20 may be smoothened such that it has a gloss factor higher than 80. The use of smoothened inner surface further increases specular reflection at the inner surface of the cap 20, which enhances dispersion and color mixing throughout the light source. Alternatively, or additionally, at least a portion of the inner cap surface may be coated with a partially reflective layer. Preferably, such coated portion includes the protrusion surface. A suitable material that may be part of such partially reflective layer is chrome.
A further improvement in color mixing can be achieved by roughening at least a portion of the outer surface of the cap 20, such that the outer surface is provided with a texture. Due to the textured outer surface light will refract at almost random angles while leaving the cap material, which greatly enhances color mixing.
Optionally, the protrusion 22 comprises a center hole 23 (denoted by dashed lines). The use of a hole 23 improves the cooling capacity of the light source. Furthermore, in case the cap 20 is made by using a molding technique, keeping the central area of the protrusion 22 free of material avoids the presence of a surplus of material at this point, which could have a negative influence on the performance of the light source in terms of uniformity of light emission in all directions.
Preferably, a cap 20 with a hole 23 is used in combination with a spatial arrangement of LEDs 3 of which the center position is free of LEDs 3. An example of such spatial arrangement is shown in
Preferably, a distance D between the top of the protrusion 22 and the center point of the spatial arrangement of LEDs 3 is at least 2 mm. The use of this minimal distance ensures that a majority of the light emitted by the LEDs 3 is not directly emitted onto the top portion of the protrusion 22. Preferably the distance D is not too large to enable light to mix throughout a large portion of the space covered by the cap 20. The spatial arrangement of LEDs 3 is often placed on a board 25. Preferably, the distance D is smaller than about half the characteristic dimension of the board 25. The characteristic dimension may vary per board shape. For example, the characteristic dimension of a rectangular structure is its diagonal, while the characteristic dimension of a circular structure is the circle diameter. So, in case the LEDs 3 are organized on a rectangular board having a diagonal of about 16 mm, the preferable maximum distance D would be about 8 mm.
The light source described above can be manufactured in the following way. First, a light unit and a cap are manufactured separately. The light unit is formed by distributing a plurality of LEDs in the form of a spatial arrangement having a center position. The plurality LEDs includes at least two different types of LEDs. Each type of LED is arranged for the emission of radiation within a different wavelength range.
The hollow curved cap is manufactured by molding a material that is substantially transparent for radiation emitted by the light unit, for example a thermoplastic such as PMMA or PC. The cap is provided with an axially symmetric protrusion forming a depression in the exterior of the cap. As described above, in some embodiments, the protrusion comprises a through hole at the center. This may be achieved by supporting the cap in such a way that the center of the protrusion, and thus also the center of the depression, remains free of molding material.
When the light unit and the cap are ready, the cap is placed over the light unit so as to cover it. The placement is such that the symmetry axis of the protrusion substantially coincides with the center position of the spatial arrangement of the plurality of LEDs.
It has been found that the point source behavior is particularly profound when the radius of a virtual hemisphere tangent to the light source is at least 10 times smaller than the radius of the virtual hemisphere tangent to the luminaire that accommodates the light source. Preferably, the radius of the virtual hemisphere tangent to the light source is smaller than 50 mm, more preferably smaller than 25 mm. A virtual hemisphere tangent to the light source of relatively small size enables the use of luminaires of relatively small size as well while still benefiting from the point source behavior of the light source.
The invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention, which is defined in the accompanying claims.
This application is a continuation of PCT application number PCT/EP2012/056000 filed on 2 Apr. 2012, which claims priority from U.S. Provisional application No. 61/470,597 filed on 1 Apr. 2011. Both applications are hereby incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 20150092419 A1 | Apr 2015 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2012/056000 | Apr 2012 | US |
| Child | 14042751 | US | |
| Parent | 61470597 | Apr 2011 | US |
| Child | PCT/EP2012/056000 | US |
