WO2014020475A1

WO2014020475A1 - Fresnel type lens for lighting applications

Info

Publication number: WO2014020475A1
Application number: PCT/IB2013/055901
Authority: WO
Inventors: Li Wei SUN; Li YUN; Huan Huang; Yanmeng Sun; Qing Guo
Original assignee: Koninklijke Philips N.V.
Priority date: 2012-07-30
Filing date: 2013-07-18
Publication date: 2014-02-06

Abstract

A lens (100) for focusing light emitted from a light source, said lens (100) having a first side (101) for facing the light source and a second side (102) opposite to the first side for facing away from the light source, wherein said lens (100) comprises: a refractive zone (103) for refracting light emitted from said light source, wherein said refractive zone (103) is arranged on said first side (101); a reflective zone (104) for reflecting light emitted from said light source, wherein said reflective zone (104) is arranged on said first side (101); and a convex top lens (105) arranged on said second side (102). The refractive zone (103) comprises a plurality of refractive elements (108) for refracting light transmitted from the light source. Thereby a lens is provided capable of producing a narrow beam pattern and at the same time having a low height.

Description

Fresnel type lens for Lighting Applications

FIELD OF THE INVENTION

The invention relates to a lens for focusing light comprising refractive and reflective zones, wherein the refractive and reflective zones is capable of focusing light.

Additionally, the invention relates to a lighting device comprising such a lens.

BACKGROUND OF THE INVENTION

Replacement of halogen spotlighting lamps by LEDs is a growing market. Replacing conventional lamps by LEDs is quite challenging since conventional lamps and LEDs have different properties. More specifically, a difference between halogen lamps and LEDs is that LEDs have a limited flux output in comparison to halogen lamps. In order for a LED spotlight to have the same maximum intensity at specific beam angles as a halogen spotlight, the optics of the LED spotlight therefore needs to provide a much higher intensity in the center of the beam per unit flux in order to compensate for the limited flux output. The intensity in the center of the beam per unit flux is often referred to as center beam candle power (CBCP) per lumen value, or simply Cd/lm or CBCP/lm.

Another practical problem is that the LED emitters are becoming larger, which makes it difficult to use conventional collimators to achieve the required narrow beam patterns.

US20050024746 discloses a refractive Fresnel lens part provided on an upper surface of a plate-like lens at a central portion. A reflective Fresnel lens part is provided on a lower surface of the plate-like lens at a peripheral portion.

However, for particular purposes the focusing achivable with such a lens is not sufficient.

In view of the above, it is thus a challenge in LED spotlighting optics to design a compact and efficient optics in a very limited space to get a higher CBCP/lm value and, good efficiency for specific beam angles.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome this problem, and to provide a lens for focusing light capable of creating narrowly without taking up to much space when used in a lighting device.

According to a first aspect of the invention, this and other objects are achieved by providing a lens for focusing light emitted from a light source, said lens having a first side for facing the light source and a second side opposite to the first side for facing away from the light source, wherein said lens comprises:

• a refractive zone for refracting light emitted from said light source, wherein said refractive zone is arranged on said first side;

· a reflective zone for reflecting light emitted from said light source, wherein said reflective zone is arranged on said first side; and

• a convex top lens arranged on said second side;

wherein the refractive zone comprises a plurality of refractive elements for refracting light transmitted from the light source.

Thereby a lens is provided capable of producing a narrow beam pattern and at the same time having a low height. This allows the lens to be used in an LED lighting device that can replace conventional halogen spots. By providing the lens with refractive elements on its inside said elements are protected from outside damage. Thereby a more robust lighting device is provided. Additionally the lens may be much less complicated to manufacture.

The lens may be known as a Fresnel or Fresnel type lens, wherein reflective zone and the refractive zone are Fresnel zones.

In an embodiment the convex top lens is a refractive convex top lens.

In an embodiment the plurality of refractive elements is a plurality of annular concentric protrusions for refracting light transmitted from the light source.

Thereby a symmetric beam pattern may be created mimicking the beam patterns known from halogen spots.

The annular concentric protrusion may have any shape e.g. be triangular protrusions or rectangular protrusions.

In an embodiment, said refractive zone further comprises a central convex spherical lens surrounded by the plurality of refractive elements.

In an embodiment the first side has a concave shape and the second side has convex shape making the lens curved.

This may further improve the focusing of the lens. Additionally this allows the lens to function at least partly as a housing for a lighting device.

In an embodiment the refractive zone is arranged in a central part of the lens and the reflective zone is arranged concentric to and surrounds the refractive zone.

In an embodiment the convex top lens is arranged in a central part of the lens. In an embodiment the lens further comprises a smooth zone arranged on said second side.

Thereby a more robust lens is provided.

In an embodiment the smooth zone is concentric with and surrounds the convex top lens. In an embodiment the widest width of the convex top lens is smaller than 150%, 125 or 110% of the widest width of the refractive zone.

In an embodiment the widest width of the convex top lens is smaller than 50% of the widest width of the lens.

In an embodiment the reflective zone comprises a plurality of annular concentric protrusions for reflecting light emitted from the light source.

Each of the annular concentric protrusions for reflecting light may be configured to reflect light emitted from the light source with different sets of angles.

Consequently, by arranging the annular concentric protrusions for reflecting light, at different positions in the reflective zone, light emitted from the light source with different angels may be reflected.

In an embodiment at least one annular protrusion of the plurality of annular concentric protrusions for reflecting light comprises a receiving part for guiding light emitted from the light source into the protrusion, and a reflecting part for reflecting light from the light source guided within the protrusion.

The receiving part may be a receiving surface. The receiving surface may be a flat surface or a curved surface.

In an embodiment the reflecting part comprises a plurality of reflecting subparts, wherein a first reflecting sub-part of said plurality of reflecting sub-parts is configured to reflect light emitted from the light source within a first set of angles, and a second reflecting sub-part of said plurality of reflecting sub-parts is configured to reflect light emitted from the light source within a second set of angles, wherein the first set of angles and the second set of angles differs so that focusing of the annular protrusion can be improved.

In an embodiment the reflecting part has a revolution surface with a generatrix as a polyline or curve.

In an embodiment the receiving part is formed by a first surface, the first reflecting sub-part is formed by a second surface and the second reflecting sub-part is formed by a third surface, wherein the second surface and the third surface are adjacent to each other.

In an embodiment the first reflecting sub-part is a part a first part of a curved surface, and the second reflecting sub-part of is a second part of the curved surface.

In an embodiment said refractive zone, said reflective zone and said convex top lens are integrally formed.

In an embodiment the lens is a lens for a spot light.

According to a second aspect of the invention, there is provided a lighting device comprising a lens as specified in relation to the first aspect of the invention, and a light source, wherein said lens is arranged to focus light emitted from said light source.

In an embodiment the light source is a light emitting diode (LED). In an embodiment the bottom of said lend is approximately on level with the middle of the light source so that light emitted approximately at any forward direction from the light source is focused by said lens.

It is noted that the invention relates to all possible combinations of features recited in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.

Fig. 1 shows a middle- view of a lens for focusing light according to the invention in an embodiment comprising a reflecting zone, a refracting zone arranged on first side of the lens and a convex top lens arranged on a second side of the lens, wherein the refractive zone comprises a plurality of refractive elements.

Fig. 2 shows ray path in the lens shown in Fig. 1.

Fig. 3 shows a middle- view of a lens for focusing light according to the invention in an embodiment wherein a first annular protrusion for reflecting light comprises a receiving part for guiding light emitted from a light source into the protrusion, and a reflecting part for reflecting light from the light source guided within the protrusion, wherein the reflecting part comprises a first reflecting sub-part and a second reflecting sub-part, wherein the first reflecting sub-part is configured to reflect light emitted from the light source within a first set of angles, and the second reflecting sub-part is configured to reflect light emitted from the light sources within a second set of angles.

Fig. 4 shows ray paths for three different lenses, a first lens according to the invention in an embodiment comprising a reflecting zone, a refracting zone arranged on first side of the lens and a convex top lens arranged on a second side of the lens, a second lens comprising a reflecting zone and a refracting zone arranged on a first side of the lens, and a third lens comprising a reflecting zone, arranged on first side of the lens and a convex top lens arranged on a second side of the lens.

Fig. 5 shows resulting beam profiles for the three lenses shown in Fig. 4.

Fig. 6 shows a middle- view of a lighting device according to the invention in an embodiment comprising a lens and a light source.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

Fig. 1 shows a middle- view of an embodiment of a lens 100 for focusing light according to the invention.

The lens 100 for focusing light according to the invention generally comprises a first side 101 for facing a light source (not shown) and a second side 102 opposite to the first side 101 for facing away from said light source. The lens 100 further comprises a refractive zone 103 arranged on the first side 101, a reflective zone 104 arranged on the first side 101, and a convex top lens 105 arranged at the second side 102. The refractive zone further comprises a plurality of refractive elements 108 for refracting light emitted from a light source i.e. the refractive elements is configured so that light emitted from a light source typically positioned in the center of the lens, is refracted when it propagates from the outside medium (typically air) and into the lens.

Thus surfaces of the refractive elements 108 facing towards the light source are angled so that light traveling from the light source will hit the interface between the outside medium and said surfaces with an angle below the critical angles so that light is not reflected. As is known to the skilled person the critical angle is dependent on the difference in the refractive index between the outside medium and refractive elements 108. Additionally, as is known to the skilled person a part (typically a minor part) of light emitted from the light source hitting the interface between the outside medium and the refractive elements 108 with an angle below the critical angle will be reflected. The refractive elements 108 may be configured so that light is redirected in a direction towards the central axis of the lens, improving the focusing of the lens 100. In the embodiment shown in Fig. 1 the refractive elements 108 are a plurality of annular concentric protrusions. The refractive zone 103 may optionally comprise a convex bottom lens 107.

The reflective zone 104 is configured to reflect light emitted from the light source. The reflective zone may comprise a plurality of reflective elements for reflecting light. The plurality of reflective elements may be a plurality of annular concentric protrusions configured to reflect light. A reflective element may comprise a receiving part having a surface facing the light source wherein said surface is arranged so that light from the light source hits said surface with an angle below to critical angle, whereby light is guided into the reflective element, and possibly refracted. Additionally a reflective element may comprises a reflecting part having a surface arranged so that light emitted from the light source and guided within the reflective element by the receiving part hits said surface with an angle above the critical angle whereby the light is reflected. The surface of the reflecting part may be arranged so that light is reflected in a direction towards the central axis of the lens, thereby enhancing the focusing of the lens. In the embodiment shown in Fig. 1 the reflective zone 109 comprises a plurality of triangular annular concentric protrusions. The first side of the lens 101 has a concave shape and the second side 102 of the lens has a convex shape thereby making the lens a curved lens. The refractive zone 103 is arranged in a central part of the lens 100 and the reflective zone 104 is arranged concentric to and surrounds the refractive zone 103. The curved top lens 105 is arranged centrally. The curved top lens 105 is surrounded by a smooth part 106. In the embodiment shown the width of the convex top lens 105 approximately corresponds to the width of the refractive zone 103.

Fig. 2 shows ray path in the lens shown in Fig. 1 for light emitted from a light source positioned at 200. It can be seen that light emitted from the light source 200 hitting the lens 100 in the refractive zone 103 will be refracted a first time when it enters the lens at the interface between the outside medium and a surface of the refractive zone 103 and further refracted a second time when it exits the lens at the interface between the outside medium and the convex top lens. Generally, both the first and the second refraction guide the light in a direction towards the central axis of the lens.

It can further be seen that light emitted from the light source 200 hitting the lens in the reflective zone 104 is refracted a first time (generally) in a direction away from the central axis of the lens when it enters a reflective element at the interface between the outside medium and a surface of the receiving part of the reflective element. Then the light is guided within the reflective element towards a surface of the reflective part of the reflective element where the light is reflected in a direction towards the central axis of the lens. Finally the light is refracted a second time when it leaves the lens at the interface between smooth zone of the lens and the outside medium (generally) in a direction towards the central axis of the lens.

Fig. 3 shows a middle- view of a lens for focusing light according to the invention in an embodiment wherein an annular protrusion 203 for reflecting light comprises a receiving part 210 for guiding light emitted from a light source into the protrusion in the form of a first surface 210, and a reflecting part 213 for reflecting light from the light source guided within the protrusion, wherein the reflecting part 213 comprises a first reflecting subpart 211 and a second reflecting sub-part 212, wherein the first reflecting sub-part is configured to reflect light emitted from the light source within a first set of angles, and the second reflecting sub-part is configured to reflect light emitted from the light sources within a second set of angles wherein the first set of angles and the second set of angles differs. This may be achieved by having a reflecting part 213 comprising a second surface 211 and a third surface 212 as shown in the figure. Alternatively, the reflecting part 213 may comprise a single surface, wherein the surface is curved i.e. the first reflecting sub-part 211 will be a first part of the curved surface and the second reflecting sub-part 212 will be a second part of the curved surface. Having a reflecting part comprising two sub-parts provides improved control of the optical performance of the lens and thereby improved focusing. It further allows larger reflecting elements to be used i.e. fewer reflecting elements. This may lower the production costs. Fig. 4 shows ray paths for three different lenses, a first lens 401 according to the invention in an embodiment comprising a reflecting zone, a refracting zone arranged on first side of the lens and a convex top lens arranged on a second side of the lens, a second lens 402 comprising a reflecting zone and a refracting zone arranged on a first side of the lens, and a third lens 403 comprising a reflecting zone, arranged on first side of the lens and a convex top lens arranged on a second side of the lens. Fig. 5 shows resulting beam profiles for the three lenses shown in Fig. 4. The horizontal axis shows degrees and the vertical axis shows intensity of the beam.

It can be seen that the first lens 401 according to the invention, has a better focusing with a higher peak intensity, and a narrower beam profile.

Fig. 6 shows a middle- view of a lighting device 600 according to the invention in an embodiment comprising a lens 601 and a light source 602.

The light source 602 is a light emitting diode; however other light sources may be used. The light source is positioned at the central axis of the lens 601. The shown lighting device is a spot light that is suitable for use in household lighting.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, the lens may be a flat lens, the refractive elements do not need to be triangular protrusions, and the relative dimension of the different zones may differ e.g. the refractive zone may be large than the reflective zone.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

Claims

A lens (100) for focusing light emitted from a light source, said lens (100) having a first side (101) for facing the light source and a second side (102) opposite to the first side for facing away from the light source, wherein said lens (100) comprises:

a refractive zone (103) for refracting light emitted from said light source, wherein said refractive zone (103) is arranged on said first side (101);

a reflective zone (104) for reflecting light emitted from said light source, wherein said reflective zone (104) is arranged on said first side (101); and a convex top lens (105) arranged on said second side (102); wherein the refractive zone (103) comprises a plurality of refractive elements (108) for refracting light transmitted from the light source.

A lens (100) according to claim 1, wherein the plurality of refractive elements is a plurality of annular concentric protrusions (108) for refracting light transmitted from the light source.

A lens (100) according to any of claims 1 to 2, said refractive zone (103) further comprises a central convex spherical lens (107) surrounded by the plurality of refractive elements (108).

A lens (100) according to any of claims 1 to 3, wherein the first side (101) has a concave shape and the second side (102) has convex shape making the lens (100) curved.

A lens (100) according to any of claim 1 to 4, wherein the lens (100) further comprises a smooth zone (106) arranged on said second side (102).

A lens (100) according to claim 5, wherein the smooth zone (106) is concentric with and surrounds the convex top lens (105).

A lens (100) according to any of claims 1 to 6, wherein the reflective zone (104) comprises a plurality of annular concentric protrusions for reflecting light emitted from the light source. A lens (100) according to claim 7, wherein at least one annular protrusion (203) of the plurality of annular concentric protrusions for reflecting light comprises a receiving part (210) for guiding light emitted from the light source into the protrusion, and a reflecting part (213) for reflecting light from the light source guided within the protrusion.

A lens (100) according to claim 8, wherein the reflecting part (213) comprises a plurality of reflecting sub-parts (211, 212), wherein a first reflecting sub-part (211) of said plurality of reflecting sub-parts (211, 212) is configured to reflect light emitted from the light source within a first set of angles, and a second reflecting sub-part (212) of said plurality of reflecting sub-parts (211, 212) is configured to reflect light emitted from the light source within a second set of angles, wherein the first set of angles and the second set of angles differs so that focusing of the annular protrusion (203) can be improved.

A lens according to any of claims 8 to 9, wherein the reflecting part (213) has a revolution surface with a generatrix as a polyline or curve.

A lens (100) according to claim 9, wherein the receiving part (210) is formed by a first surface, the first reflecting sub-part (211) is formed by a second surface and the second reflecting sub-part is formed by a third surface (212), wherein the second surface and the third surface are adjacent to each other..

A lens (100) according to any of claims 1 to 11, wherein the lens is a lens (100) for a spot light.

A lighting device (400) comprising a lens (100) according to any of claims 1 to 12, and a light source (402), wherein said lens (100) is arranged to focus light emitted from said light source (402).

A lighting device (400) according to claim 13, wherein the light source (402) is a light emitting diode (LED).

A lighting device (400) according to any of claims 13 to 14, wherein the bottom of said lens (100) is approximately on level with the middle of the light source (402) so that light emitted approximately at any forward direction from the light source (402) is focused by said lens (100).