DESCRIPTION

TECHNICAL FIELD

The present invention relates to a chip-on-board (COB) type LED lighting unit capable of guiding light ideally with no lens.

BACKGROUND OF THE INVENTION

The COB LED lighting units mainly comprise various LED chips arranged directly on a printed circuit board (PCB). LED chips are bonded to the printed circuit board by means of an adhesive with a high thermal conductivity and electrical connection is established between the LED and conductive lines formed on the printed circuit board by means of conductive wires. At the bottom of the printed circuit board, a cooling layer is provided which is made of a material with high conductivity, such as aluminum, ceramic etc. Thus, the heat flow from the LED towards the printed circuit board is discharged.

At the upper portion of the LEDs which is opened to allow exit of the light, a phosphor-containing silica gel or an epoxy resin-containing window layer is provided. When it is desired to illuminate a certain area with the light, lenses used are also arranged on this window layer. Lenses may considerably affect efficiency of a LED lighting unit. In fact, lenses may have deficiencies in light guiding functions because of manufacturing errors. Furthermore, when the incident light is guided by a lens, a portion of light is reflected back, which results in a loss of efficiency of the lighting unit.

Essentially, the geometric form of the printed circuit board imposes to use a lens in a COB LED lighting unit of a known configuration. As shown in Figures 1 and 2, the known COB LED printed circuit board (similarly, the underlying cooling layer for heat transfer) has a flat form. Therefore, lenses must be used if a certain area is to be illuminated by the light at an angle of 60°, 90° and 120°.

DESCRIPTION OF THE INVENTION

An object of the invention is to increase efficiency of COB LEDs in an effective manner.

In order to achieve the above object, the present invention relates to a COB LED lighting unit comprising a printed circuit board, and at least one LED positioned thereon, wherein the printed circuit board has a form which is at least partially curved and the at least one LED is positioned on the said at least partially curved form; wherein the COB LED lighting unit does not comprise a lens for guiding the LED light.

In an embodiment of the invention, the printed circuit board has a form of a concave ellipsoid or a spherical cap surface.

In an embodiment of the invention, the printed circuit board has at least two forms with different curvatures.

In an embodiment of the invention, the printed circuit board comprises at least one flat surface and at least one curved surface. In an embodiment of the invention, it comprises a cooling layer associated with the lower portion of the said printed circuit board and the form of the said cooling layer preferably corresponds to that of the printed circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of a COB LED array according to the prior art. Figure 2 is a sectional view of a COB LED array according to the prior art. Figure 3 is a perspective view of a COB LED array according to the invention.

Figure 4 is a sectional view of a COB LED array according to the invention. Figure 5 is a sectional view of an alternative embodiment of a COB LED array according to the invention.

REFERANCE NUMBERS OF THE PARTS IN THE DRAWINGS 1 Printed circuit board

2 LED

3 Cooling layer

4 Curved surface

5 Flat surface

DETAILED DESCRIPTION OF THE INVENTION

In order to provide a better understanding of the invention, LED arrays of the COB LED lighting unit according to the invention are shown in the drawings. Accordingly, the COB LED lighting unit comprises a number of - at least one - LEDs (2), a printed circuit board (1) on which LEDs are positioned, and a cooling layer (3) covering the printed circuit board (1) underside. Since the operational connection of these components is known from the prior art, description thereof is omitted.

As shown in Figure 3, the printed circuit board (1) has a concave and ellipsoid cap surface form. The LEDs are suitably distributed on this surface. The curve of the printed circuit board (1) and the way in which the LEDs are distributed thereon may vary depending on the diffusion of the light desired in the area to be illuminated. For example, if a symmetrical light area is desired, it is likely that the printed circuit board (1) displays a form of a concave spherical cap surface and the LEDs are, in turn, arranged on the printed circuit board (1) in the corresponding number and with a uniform distribution. On the other hand, if the area desired to be illuminated is, for example, a street, an avenue etc., it may be suitable to use a printed circuit board (1) with an asymmetric geometry, as shown in Figure 5. Said asymmetric geometry may for example be comprised of a section of the printed circuit board (1) that comprises a curved surface (4) and a section thereof that comprises a flat surface (5). Likewise, the printed circuit board (1) may have at least two curved forms with different curves, based on the lighting needs of the area to be illuminated.

As shown in Figures 4 and 5, the cooling layer (3) which is located underside of the printed circuit board (1) has a form corresponding to that of the printed circuit board (1). However, in view of the conditions of an environment where the COB LED lighting unit is to be used, especially a cold outer environment, mounting tolerances should be considered, taking into consideration of expansions arising from the temperature differences.

The printed circuit board (1), though not illustrated in the drawings, may have a convex surface form, and the light may be focused on the desired region by arranging the LEDs on the convex surface in the corresponding number and with a suitable shape.

With the curved form of the printed circuit board (1) and the LEDs (2) arranged thereon in a suitable manner, an ideally lens-free COB LED lighting unit is achieved. Optionally, the COB LED lighting unit may comprise a conventional reflector. Similarly, it may comprise, at the upper portion of the LEDs which is opened to allow exit of the light, a phosphor-containing silica gel or an epoxy resin-containing window layer.