Light emitting strip

The present invention relates to a light emitting strip (10), comprising: an elongate body (12); at least one light source (16) adapted to emit light into the elongate body; and a gap (24) in the elongate body, which gap is arranged in front of the at least one light source, wherein the gap is adapted to omnidirectionally distribute, in a plane (26) perpendicular to a longitudinal direction of the light emitting strip, light emitted by the at least one light source. The present invention also relates to a method of manufacturing a light emitting strip (10).

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2018/067945, filed on Jul. 3, 2018, which claims the benefit of European Patent Application No. 17181199.5, filed on Jul. 13, 2017. These applications are hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to a light emitting strip, for example a light emitting diode (LED) strip. The present invention also relates to a method of manufacturing a light emitting strip.

BACKGROUND OF THE INVENTION

LED strips are available in a large variety. However, almost all of them have a one sided Lambertian luminous intensity distribution. In a lot of use cases this is very inconvenient, for example if the LED strip is free hanging instead of being mounted on a wall or ceiling.

US2014098535 relates to a segmented LED lighting system. In particular, US2014098535 discloses a set of channel segments connected by a flexible lens sleeve that can be positioned in a variety of ways. A printed circuit board with at least one LED is mounted in each channel segment. Each segment preferably has a base with two ribbed vertical sides. The lens sleeve is preferably coextruded from flexible acrylic and has opaque side grips that grip the ribbed vertical sides and a translucent lens portion with an air gap to help proper diffraction of the light along the length and width of the lens sleeve.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome or at least alleviate the aforementioned problem(s), and to provide an improved light emitting strip.

According to a first aspect of the invention, this and other objects are achieved by a light emitting strip, comprising: an elongate body; at least one light source adapted to emit light into the elongate body; and a gap in the elongate body, which gap is arranged in front of the at least one light source, wherein the gap is adapted to omnidirectionally distribute, in a plane perpendicular to a longitudinal direction of the light emitting strip, light emitted by the at least one light source.

The present invention is based on the understanding that a gap, for example an air gap, in the body of the strip may be shaped and/or positioned such that light from at least one light source, even if the light is emitted from the light source(s) in only one main direction, can be omnidirectionally distributed, i.e. distributed in basically all directions, in a plane perpendicular to the longitudinal direction of the light emitting strip.

By means of the present omnidirectional light emitting strip, the mounting direction of the strip becomes unimportant. Also, any twisting of the strip would not result in any visible effect. When for example the present light emitting strip is free hanging, it is possible and very favourable to get a homogenous light effect over the total length of the strip.

The gap may be arranged such that a first part of the light emitted by the at least one light source passes the gap and such that a second part of the light emitted by the at least one light source is reflected back towards a plane in which the at least one light source is situated but preferably not towards the at least one light source itself or towards any support for the at least one light source. This may be achieved by having a first interface between the elongate body and the gap, which first interface is proximal to the at least one light source and dual arches-shaped, and a second interface between the elongate body and the gap, which second interface is distal to the at least one light source. The second interface may be single arch-shaped. The second part may be reflected back by at least two total internal reflections at an interface between the elongate body and the gap, which interface for example may be the aforementioned first interface.

The at least one light source together with any support for the at least one light source may be arranged in the elongate body. For example, the at least one light source together with the support, if any, may be arranged in a space in the elongate body.

The elongate body may have a circular cross-section. The circular shape may beneficially match the omnidirectional lighting function; it has no preferred orientation and it does not change appearance when the lighting device is somewhat twisted.

The light emitting strip may further comprise an elongate diffuse outer part at least partly encircling the elongate body. The elongate diffuse outer part may homogenize the emitted light further and prevent a direct look on the at least one light source. The elongate diffuse outer part may have a further function to make the optical output insensitive to scratches and dirt, by smoothening out small artefacts. Instead of the elongate diffuse outer part, the elongate body could have a rough outer surface or a thin white coating.

The thickness of the elongate diffuse outer part may vary along the circumferential direction of the elongate diffuse outer part. The elongate diffuse outer part may for example the thicker in a main light emitting direction of the at least one light source and thinner in the opposite direction, to balance the asymmetry in case of top-emitting light sources.

The elongate diffuse outer part may comprise scattering particles, wherein the density of scattering particles varies along the circumferential direction of the elongate diffuse outer part. The density may for example be higher in a main light emitting direction of the at least one light source and lower in the opposite direction, to balance the asymmetry in case of top-emitting light sources.

The elongate body and the elongate diffuse outer part may be co-extruded. The elongate body and elongate diffuse outer part may hence collectively be referred to as a co-extruded or co-extrusion profile.

The gap may have a shape as illustrated in figures of the present application.

According to a second aspect of the invention, there is provided a method of manufacturing a light emitting strip, which method comprises: co-extruding a central elongate body and an elongate diffuse outer part; and providing at least one light source adapted to emit light into the elongate body, wherein a gap in the elongate body is arranged in front of the at least one light source, and wherein the gap is adapted to omnidirectionally distribute, in a plane perpendicular to a longitudinal direction of the light emitting strip, the light emitted by the at least one light source. This aspect may exhibit the same or similar features and technical effects as the first aspect, and vice versa.

As illustrated in the figures, the sizes of layers and regions may be exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of embodiments of the present invention. Like reference numerals refer to like elements throughout.

DETAILED DESCRIPTION

FIGS. 1 and 2a-cillustrate a light emitting strip10according to one or more embodiments to the present invention. The light emitting strip10may be a flexible omnidirectional light emitting diode (LED) strip. It is appreciated from the drawings and the following description that the light emitting strip10does not have to be flat. Instead, the light emitting strip10may (overall) be shaped like a rope or string.

The light emitting strip10comprises a (central) elongate body12. The elongate body12may for example have a length in the range of 1-10 m (for indoor applications) or 1-100 (for outdoor applications), which length may correspond to the overall length of the light emitting strip10. The elongate body12may be flexible. The elongate body12may be transparent (clear) or somewhat translucent. The elongate body12may for example be made of or comprise silicone, thermoplastic elastomer (TPE), PVC, PMMA, or Polycarbonate. The elongate body12may have a circular cross-section perpendicular to the length of the elongate body12, as seen inFIGS. 2a-c. In particular, the outer circumference of the elongate body12is circular. The diameter of the elongate body12may be in the range of 5-50 mm, typically in the range of 10-30 mm.

The light emitting strip10further comprises at least one but preferably several light sources16adapted to emit light into the elongate body12. The light sources16may be mounted on an elongate support14. The elongate support14may have (substantially) the same length as the elongate body12. The elongate support14is here a flexible printed circuit, and the light sources16are light emitting diodes. The light sources16are positioned on one side18of the elongate support14, and they may be mounted one after the other in the longitudinal direction of the elongate support14. There is typically a distance between successive light sources16. The light sources16may be facing the same direction. The light sources16may be top emitting devices having a main light emitting direction20. The elongate support14and the light sources16may be arranged in an air-filled space22in the elongate body12. The space22may for example have a rectangular shape, as seen inFIGS. 2a-c.

The at least one light source could alternatively be organic light emitting diodes or laser diodes mounted on the elongate support14, or one strip-shaped light source for example a flexible electroluminescent strip or a flexible organic LED strip without separate support. Also, instead of being a flexible printed circuit, the elongate support14could be just wires or flat cable wires on which the light sources16are directly mounted, or a plurality of small rigid boards interconnected by a flexible mechanical and electrical connection.

The light emitting strip10further comprises a gap24in the elongate body12The gap24may have (substantially) the same length as the elongate body12. The gap24may be referred to as an elongate gap. The gap24may be an air gap, or the gap24may be filled with a material with a lower index of refraction than the material of the elongate body12. The gap24is arranged in front of the light sources16, i.e. in the main light emitting direction20of the light sources16. The gap24is generally adapted to omnidirectionally distribute—in a plane26perpendicular to a longitudinal direction of the light emitting strip10—light emitted by the light sources16. The gap24is shaped and positioned relative to the light sources16such that a first part28aof the light emitted by the light sources16may pass the gap24and such that a second part28bof the light emitted by the light sources16may be reflected back towards a plane30in which the light sources16are situated (seeFIG. 2b), but not directly towards the elongate support14and the light sources16. Namely, the light emitting strip10has first and second interfaces32a-bbetween the elongate body12and the gap24. The first interface32ais proximal to the light sources16, and the second interface32bis distal to the light sources16. Furthermore, the first interface32ais dual arches-shaped, as seen inFIGS. 2a-c. That is, the first interface32ahas the shape of two arches, which are connected at an intermediate point34. The intermediate point34may be positioned centrally over the light sources16. The arches of the first interface32amay be (semi-) circular, segmented, pointed, inverted V-shaped, etc. The second interface32bis single arch-shaped, as seen inFIGS. 2a-c. That is, the first interface32ahas the shape of one arch, which arch connects with the outer points36a-bof the two arches of the first interface32a. The gap24should be wider than the at least one light source16(and the elongate support14), so that as much as possible of the light reflected back can pass the at least one light source16(and the support14). The shape of the gap24as seen inFIGS. 2a-c, as well as other shapes seen in those cross-sectional views, may be uniform throughout the length of the light emitting strip10.

The aforementioned second part28bmay be at least 10% or at least 20% but preferably not more than 50% of the light emitted by the light source(s)16as seen in plane26, whereas the first part28aconstitutes the rest of the light emitted by the light source(s)16in plane26. The first part28amay for example be 50% of the light emitted by the light source(s)16and the second part28bis 50% of the light emitted by the light source(s)16.

The light emitting strip10may further comprise an elongate diffuse outer part38. The elongate diffuse outer part38may have (substantially) the same length as the elongate body12. The elongate diffuse outer part38here completely encircles the elongate body12, as seen inFIGS. 2a-c. The elongate diffuse outer part38may for example be made of or comprise the same material as the elongate body12, i.e. silicone, thermoplastic elastomer (TPE), PVC, PMMA, or Polycarbonate. InFIGS. 2a-c, the thickness of the elongate diffuse outer38varies along the circumferential direction40of the elongate diffuse outer part38. Namely, the elongate diffuse outer part38is thicker (=more diffusion) in the main light emitting direction20and thinner in the opposite direction, to balance the asymmetry of top-emitting light sources16. The thickness in the main light emitting direction20may for example be in the range of 3-20 mm and the thickness in the opposite direction may be in the range of 0-5 mm or 0.5-5 mm. The thickness may for example vary between 10 mm (top) and 3 mm (bottom) or between 20 mm (top) and 1 mm (bottom). In case the elongate diffuse outer part38only partly encircles the elongate body12, the thickness opposite the main light emitting direction20may be 0 mm.

In another embodiment shown inFIG. 3, the elongate diffuse outer part38comprises scattering particles42, for example white paint material (such as titanium oxide) or any clear material with a refractive index different than that of the remaining elongate diffuse outer part38(such as air bubbles, PC particles, PMMA particles, silicone, glass, etc.). The density of scattering particles42may vary along the circumferential direction40. The density may for example be higher (=more scattering/diffusion) in the main light emitting direction20and lower in the opposite direction, to balance the asymmetry of top-emitting light sources16. The thickness of the elongate diffuse outer38may in this embodiment be uniform along the circumferential direction40.

In operation of the light emitting strip10, the light sources16emit light, wherein some (first part28a) of the light passes the gap24, whereas some (second part28b) of the light is reflected back towards the plane30by at least two total internal reflections at the first interface32a, resulting in an omnidirectional luminous intensity distribution, as shown inFIG. 2b. That is, the gap24(re)distributes light emitted by light sources16uniformly along the circumference of the light emitting strip10. The elongate diffuse outer part38further homogenizes the light, as shown inFIG. 2c.

FIG. 4is a flow chart of a method of manufacturing the light emitting strip10. The method comprises the steps of co-extruding (S1) the central elongate body12(including the space22and gap24) and the elongate diffuse outer part38, and providing (S2) the at least one light sources16adapted to emit light into the elongate body12. The latter step may include inserting the elongate support14and/or the light source(s)16into the space22during or after the co-extruding step.

The light emitting strip10can be used indoors or outdoors, as a direct or indirect light source. The light emitting strip10may have enough light output to create the best ambiance, or for practical purposes like soft security and navigation lighting and architectural lighting.