FIELD OF THE INVENTION

This invention relates to a lamp comprising a light source and a reflector for redirecting light from the light source into a main direction, the reflector comprising a plurality of translucent parts for allowing part of the light from the light source to leave the lamp in a direction extending from the light source through the reflector.

BACKGROUND OF THE INVENTION

Such a lamp is, e.g., known from the United States patent application published as US 2011/0233593 Al. Said patent application discloses a LED lamp with a bowl-shaped heat dissipater. The inner surface of the heat dissipater also functions as a reflector for distributing and redirecting the light into a main direction. The heat dissipater comprises multiple windows (through-holes filled with translucent members). The windows are provided for deliberately leaking part of the emitted light out of the heat dissipater. The light leaking through the windows travels in a direction different from the direction of the light reflected at the inner surface of the bowl-shaped heat dissipater.

The use of translucent parts, however, comes with some disadvantages. A first disadvantage is that the translucent material causes a change of color. Commonly used translucent materials tend to filter the blue part of the light. Light leaving the lamp through the translucent parts at the back of the heat dissipater is therefore more yellow/orange than the light reflected at its inner surface. Furthermore, the translucent material absorbs part of the light and thereby reduces the efficiency of the lamp. An additional disadvantage follows from the orientation of the through-holes, which is such that light from the light source follows a straight line through the windows and leaves projections on a surface on which the light is incident.

OBJECT OF THE INVENTION

It is an object of the invention to provide a lamp in which part of the light is emitted in a different direction, and in which all of the above-mentioned disadvantages have been overcome. SUMMARY OF THE INVENTION

According to a first aspect of the invention, this object is achieved by providing a lamp comprising a light source and a reflector for redirecting light from the light source into a main direction, the reflector comprising a plurality of holes for allowing part of the light from the light source to leave the lamp in a direction extending from the light source through the reflector, the holes in the reflector having reflective inner walls and being dimensioned and oriented such that any light rectilinearly propagating from the light source into the holes is reflected by the inner walls at least once before leaving the holes.

When holes are used instead of translucent material, the color of the light is maintained and absorption is reduced. However, the use of holes may lead to further problems that are also overcome by the lamp according to the invention. A disadvantage of using holes is that the light source is directly visible at the back of the reflector or, if e.g. a diffuser covers the lamp, as a projection on the diffuser. When multiple light sources are used, the different light sources are not blended and can be distinguished as individual light sources. In, e.g., a Wake-Up lamp, it is important to provide semi-natural general lighting of the room and to avoid the impression of individual, artificial light sources.

The desired semi-natural general lighting experience is obtained by providing the holes in the reflector with reflective inner walls and by ensuring that the holes are shaped and positioned in such a way that the light from the light source will always be reflected at the inner wall of one of the holes at least once, before leaving the lamp at the rear side of the reflector (the front side being the reflector surface redirecting the light into the main direction). The reflection of the light at the inner walls of the holes causes the light to leave the holes (and the lamp) in many different directions and there is no direct light path from the source through the holes to a projection surface. As a result, the light leaving the lamp at the back of the reflector is diffuse and individual light sources cannot be distinguished. The ratio of light leaving at the front and light leaving at the back of the lamp is determined by the size and number of the holes.

In an embodiment, the holes have a uniform cross-section with a width (W), at least over a length (L), and, for each hole, an angle (a) between a longitudinal axis of the hole and a straight line extending from the light source to an entrance point of the hole closest to the light source is greater than arctan(W/L). With such dimensions and orientation, the light from the light source is guaranteed to be reflected at an inner wall of the holes at least once before leaving the reflector. When a > arctan(2W/L), the light will be reflected by an inner wall of the holes at least twice.

In an embodiment of the lamp according to the invention, the length (L) of the holes is defined by a thickness of the reflector and an orientation of the hole relative to a surface of the reflector. This is the case when the hole has straight walls and runs from the front surface of the reflector to the back surface of the reflector. The hole is not necessarily aligned perpendicularly to one (or both) of the reflector surfaces, but may be provided at an angle with respect to the surface normal. Such orientation may help to provide holes of sufficient length, in case the thickness of the reflector itself would not enable a sufficient length of the holes.

In a preferred embodiment, the length (L) of the holes is increased by extension tubes. Also the inner walls of the extension tubes are reflective. These tubes may be provided at the front and/or rear surface of the reflector. The orientation of the extension tube relative to the light source may be substantially the same as the orientation of the hole, but may also be different, e.g. to increase the amount of reflections inside the tube.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Figure 1 shows a cutaway drawing of a lamp according to the invention, Figures 2 and 3 schematically show cross-sections of part of a reflector with holes, and

Figures 4, 5 and 6 schematically show cross-sections of parts of reflectors with holes and extension tubes.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows a cutaway drawing of a lamp 10 according to the invention. In this example, the lamp is a wake-up light 10 that is used to wake up people by switching on and gradually increasing its brightness around the time a user wants to wake up. The wake-up light 10 is designed to mimic the natural wake-up process by providing the overall general lighting experience of a normal sunrise. For a wake-up light 10, it is therefore important to emit light into different directions and not give the impression of individual light sources illuminating the area. It is, however, to be noted that the inventive reflector that will be described hereinafter can also be used in other lighting applications.

The lamp 10 comprises a light source 11 and a reflector 12. The light source 11 may be any kind of light source, e.g. an incandescent light bulb, a gas discharge lamp or a LED lamp. The reflector 12 is made of or covered with a reflective material in order to redirect most of the light coming from the light source 11 towards the front side 28 of the lamp 10. The reflector 12 may, e.g., be made of metal or plastics. For example, polycarbonate or polybutylene mixed with titanium-dioxide (Ti0 ₂ ) may be used, wherein Ti0 ₂ provides the reflective properties. If the reflector material itself does not have the desired reflective properties, a reflective coating may be applied.

The reflector 12 comprises a plurality of holes 13 for allowing part of the light from the light source 11 to leave the lamp 10 at the back side 29. The holes 13 have a reflective inner wall for reflecting the light at least once before it leaves the hole 13. Like the reflector surface, the reflective inner wall of the holes 13 may be reflective because the reflector 12 is made of a reflective material or because a reflective coating is used. The orientation and dimensions of the holes 13 determine how often the light is reflected before it reaches the back of the reflector 12. In different holes 13, the light is reflected into different directions, which causes the light at the back of the lamp 10 to be diffuse. In addition, the internal reflections at the inner walls of the holes 13 also cause the light leaving a single one of the holes 13 to be diffuse. The longer the holes 13, the more internal reflections there are and the more diffuse the light is. Extension tubes 14 may be provided at either (or both) sides of the holes to increase their length. Further details of the holes 13 and the extension tubes 14 are provided below with reference to figures 2 to 6.

Figures 2 and 3 schematically show cross-sections of part of a reflector 12 with holes 13. The hole 13 shown in this figure is a tube with a length L equal to a thickness D of the reflector 12. In this example, the hole 13 is tubular, but it may also be rectangular or any other shape. It is only important that the hole 13 is a through hole, such that light that enters the hole at one side can leave the hole 13, after one or more reflections, at the other side. The hole 13 has a uniform cross-section with a diameter W. The cross-section is not necessarily uniform over the whole length of the hole, but may vary. The inner wall of the hole 13 is provided with a reflective coating 31. Such a coating 31 is necessary only when the reflector material 12 itself is not reflective for light of the relevant wavelength.

The minimum length L for providing at least one internal reflection depends on the other dimensions of the hole 13 and the orientation with respect to the lamp 11. Here, we describe the orientation by defining an angle a between a longitudinal axis of the hole 13 and a straight line extending from the 'top' of the light source 11 to an entrance point at the inner wall of the hole 13 closest to the light source 11. Of course, if the light source 11 were positioned above the hole 13, the angle a would be defined as the angle between the longitudinal axis of the hole 13 and a straight line extending from the 'bottom' of the light source 11 to an entrance point at the inner wall of the hole 13 closest to the light source 11. The minimum length L of the hole 13 is given by the equation:

L > W I (tan a)

For the orientation of the hole, this means that:

a > axctaniWIL)

If at least two internal reflections are desired, the minimum length changes to:

> (2iP) / (tan a)

and the orientation angle a to:

a > axctanilWIL)

Figure 3 shows how changing the orientation of the hole may result in additional internal reflections because the light does not have to travel as far before reaching the other wall. An additional advantage of changing the orientation of the hole 13 relative to the reflector surface is that the length L of the inner walls may be larger than the thickness D of the reflector 12, which might also increase the number of internal reflections.

Figures 4, 5 and 6 schematically show cross-sections of parts of reflectors 12 with holes 13 and extension tubes 14. At the inner wall of the extension tube 14, a reflective coating 41 is provided. Such a coating 41 is necessary only if the tube material 14 itself is not reflective for light of the relevant wavelength. The tubes 14 may or may not be made of the same material as the reflector. The extension tube 14 elongates the hole 13 and thus increases the amount of internal reflections. Using such tubes 14, it is consequently not necessary to use very thick reflectors 12. It is only important that the reflector 12 and the extension tube 14 together provide a hole 13 of sufficient length L in relation to its width J and orientation.

As seen in Figure 5, also when extension tubes 14 are used, it may still be beneficial to choose an orientation for the hole 13 that is not perpendicular to the reflector surface. Figure 6 shows that the orientation of the hole 13 inside the reflector 12 may differ from the orientation inside the extension tube 14. Different orientations may be used for extension tubes 14 at different positions at the reflector surface 12. In the figures, all extension tubes 14 are provided at the back side of the reflector 12, but it is also possible to provide them at the other side.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.