Field of the Invention

The present invention relates to a field of illumination, in general, and to an illumination device based on light-emitting diodes, in particular.

Background of the Invention

Use of light-emitting diodes (LEDs) for applications requiring strong illumination has been enabled by recent efficiency improvements in commercially available LEDs that work adequately for many applications. Several applications including indoor and outdoor illumination, are still difficult to realise, however, due to several limitations, such as light efficacy, performance, cost, size, and manufacturability, which are posed by commercially available packaged LEDs.

The existing market solutions for indoor or outdoor illumination use either conventional fluorescent lamps or two flat LED panels arranged such that the light emission sources are directed in opposite directions. While conventional lamps distribute light radially in 360° of arc, most of the LEDs have a maximal 120° distribution, with a main magnitude of light that concentrates around the angle of 60°. Notwithstanding the above limitation, LED lamps are more energy efficient, do not emit heat and considered green technology. However, the narrow illumination angle does not allow the LED lamps to reach the desired uniform light distribution. For example, in case of illuminated light boxes, the LED lamps cannot achieve uniform light distribution of both screens at the same time.

CN 102748599 mentions a LED lamp comprising a plurality of the LED light sources arranged on their respective substrates attached to the triangular heat radiating sleeve, and a lamp tube cylinder.

CN 201739796 U relates to a LED fluorescent lamp comprising a lamp tube, external power supply connectors fixed at two ends of the lamp tube, an internal power supply converter, a radiator and LED light sources. This lamp is equipped with a tubular heat sink and the LED light sources arranged at intervals by 120° on the surface of the sink housing, forming a main luminous radiating framework.

US 20110019421 Al mentions a tubular LED illuminating device comprising a tubular shell, a supporting frame and a plurality of light emitting units. An inner surface of the shell forms a plurality of elongate protrusions extending along a direction parallel to an axial direction of the shell. The supporting frame is received in the shell and comprises three supporting plates.

WO 2014067329 Al mentions an LED lamp tube with a relatively large light-emitting angle. The LED lamp tube comprises a cover and plugs arranged at both ends of the cover, a hollow triangular aluminium cylinder, and a printed circuit board (PCB) assembly.

Although US 20110019421 Al and WO 2014067329 Al allegedly state that light emitted through the shell from the LEDs, may achieve a light- emission angle of 360°, in reality it is not so. Simple assembly of three LED lamps on three supporting plates at an angle of 120° does not achieve the required uniform illumination over the circle of 360° due to geometric constraints, as explained below.

It is therefore an object of the present invention to provide an improved illumination device, which allows uniform distribution of the luminous flux produced by LED light sources over 360°.

Other objects and advantages of the invention will become apparent as the description proceeds. Summary of the Invention

The present invention is a novel and improved illumination device, which allows uniform distribution of the luminous flux produced by LED light sources over 360°.

A first aspect of the present invention is an illumination device comprising:

a) an optically transparent tube having a shape comprising a plurality of concave surfaces, wherein said concave surfaces are capable of creating lens effects;

b) a plurality of light-emitting diodes (LEDs) fixed on a plurality of the LED substrates;

c) electric contacts on both ends of the LED substrates!

d) an adapter attached to the tube; and

e) an end cap covering the adapter.

Another aspect of the present invention is use of the illumination device in any indoor and outdoor illumination applications, for example two-sided illuminated light boxes in street signs, advertising stands, and the like, providing uniform light coverage over each screen. Various embodiments of the invention may allow various benefits, and may be used in conjunction with various applications. The details of one or more embodiments are set forth in the accompanying figure and the description below. Other features, objects and advantages of the described techniques will be apparent from the description and drawings and from the claims.

Brief Description of the Drawings

The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the appended figures.

Fig. 1A is a perspective view of the illumination device according to the invention;

Fig. IB is a triangular arrangement of the LEDs inside the optically transparent tube according to the invention;

Fig. 2 is a cross-section view of the optical tube profile according to the invention;

Fig. 3 is a cross-section view of the device according to the invention showing the path of light beams propagated from the illumination device of the invention containing three LEDs and placed between two screens; Pig. 4 is a cross-section view of the prior art device with three LEDs inside the tube having the equal width shell, without concave surfaces, and the path of light beams propagated from such device;

Fig. 5A is a graph of a relative luminosity as a function of a deflection (radiation) angle for the illumination device with three LEDs but without lenses!

Fig. 5B is a graph of a relative luminosity as a function of a deflection (radiation) angle for the illumination device having three LEDs with lenses;

Fig. 6A is a light flux (distribution) diagram for the illumination device having three LEDs without lenses; and

Fig. 6B is a light flux (distribution) diagram for the illumination device having three LEDs with lenses.

Dettailed Description of the Invention

In the following description, various aspects of the invention will be described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the invention. However, it will also be apparent to one skilled in the art that the invention may be practiced without the specific details presented herein. Furthermore, well-known features may be omitted or simplified in order not to obscure the invention. Although a portion of the discussion may relate to the indoor or outdoor lamps, the present invention is not limited in this regard, and embodiments of the present invention may be used in conjunction with various other devices, systems, and processes. As such, some embodiments of the invention may be used, for example, in conjunction with illumination required in biotechnological devices and in biomedical field, in general, for in vitro or in vivo applications. Some embodiments of the invention may be used not necessarily in the context of the instantly claimed applications.

In one aspect, the present invention relates to a novel and improved illumination device, which allows for uniform distribution of the luminous flux produced by LED light sources over 360°.

A first aspect of the present invention is an illumination device comprising: a) an optically transparent tube having a shape comprising a plurality of concave surfaces, wherein said concave surfaces are capable of creating lens effects;

b) a plurality of light-emitting diodes (LEDs) fixed on a plurality of the

LED substrates;

c) electric contacts on both ends of the LED substrates;

d) an adapter attached to the tube; and e) an end cap covering the adapter.

The device of the invention combines the advantages of a regular fluorescent lamp having an illumination angle of 360° and a low-energy consuming LED lamp. The illumination device overcomes the limitation of narrow lighting angle of the LED lamps and allows considerable energy saving by reducing the number of the LED substrates, which require for uniform 360° light emission.

The device comprises a plurality of LED substrates integrated into an optically transparent tube having a shape comprising a plurality of concave surfaces which are not parallel to each other, thereby creating lens effects. The special optical tube functions both as a casing of the device and as an optical instrument that allows increasing the light emission angle of LEDs and hence, achieving uniform illumination of the area.

Reference is now made to Fig. 1A showing the perspective view of the illumination device according to the invention. Optically transparent tube (l) having a plurality of concave surfaces along its outer surface is used as both a casing and an optical instrument for the LEDs mounted on their corresponding substrates (2). There are electric contacts (4) attached onto both ends of the illumination device by rivets or pins (3). In addition, adapter (5) is attached to tube (l) by means of screws (7), which firmly fix the LED substrates (2) at the permanent positions and thus prevent them from wobbling inside tube (l). Further, cap (6) at the end of tube (l) covers adapter (5) by means of screw (8). The cap incorporates electrical pins and/or plugs.

Reference is now made to Fig. IB, which shows a triangular arrangement of LEDs (10) inside the optically transparent tube. The LEDs are mounted on their corresponding substrates (2), and the substrates are held using ring (15). This is an optional design, particularly useful in cases when the optical tube is made of materials, as detailed below, which are difficult to process. In the design shown in Fig. 1A and Fig.2, the use of ring (15) is omitted, since substrates (2) are inserted directly into the tube's wall. As mentioned above, rivets or pins (3) are used to attach the electric contacts. Substrate (2) is essentially a printed circuit board (PCB) for LEDs. The PCB is commercially available or customized, if needed.

Reference is now made to Fig. 2 showing a cross-section view of optical tube (l), which represents, inter alia, an optical instrument. The shape of tube (l) comprises a plurality of concave outer surfaces (ll) and concave inner surfaces (12). LEDs (10) are mounted on substrates (2), which are firmly held by protruding rails (16) made in the wall of tube (l). The effect of expanding the light emission angle is reached by creating a concave curvature in the shapes of the transparent tube's surfaces to obtain segments of the tube in which the surfaces are not parallel to each other, thereby providing the required lens effect. The resulted pseudo-lens has a complex double-concave shape defined by outer surface (ll), which extends from point (a) to point (b), and inner surface (12), which extends from point (c) to point (d). Further, LED substrates (2) are inserted inside tube (l), as shown in Fig. 2. Tube (l) has openings (9) designed for screws (7) that connect adapter (5) to tube (l).

Optically transparent materials for tube (l) can be any inorganic or polymeric organic materials, for example fused silica, transparent ceramics (such as crystalline alumina, spinel and yttrium aluminium garnet), calcium fluoride, magnesium fluoride, zinc selenide, optical polyimides, polycarbonates etc.

Deflection angle of light emitted by LEDs and passing through the concave surfaces can be changed in three following ways: a) by changing the curvature of outer concave surface (ll); b) by changing the distance between LED (ll) and inner concave surface (12), and c) by changing the tube's material, since different materials have different refractive indices which affect the strength of deflection occurring at the boundaries of the concave surfaces due to the refraction of the light beam. In fact, points (a), (b), (c) and (d) determine the theoretical deflection angle of light emitted by any particular LED placed at certain distance from inner concave surface (12). In other words, the effect of the uniform light distribution with the LEDs can be clearly achieved by controlling the form of outer surface (ll), and inner surface (12) and/or by controlling the distance between the LED unit and the lens in front of it. In addition, when used, for example, in two-sided illuminated narrow boxes, the required form and/or required distance between a LED and a lens depend on the tube's material chosen.

Reference is now made to Fig. 3, which depicts a cross-section view of the illumination device of the present invention placed between two screens (13) at distance (B), and paths of light beams (14) propagated from these three LEDs. The aforementioned deflection angle (a) affects the size of the incident light zones (H) on screen surfaces (13), as a result of the overlap between light beams (14) when two or more LEDs are used.

Reference is now made to Fig. 4, which shows a cross-section view of a prior- art illumination device mentioned in the introductory part of the specification. As seen from Fig. 4, simple assembly of three LEDs (10) on three supporting substrates at an angle of 120°, as mentioned in the references above, does not achieve the required uniform illumination over the circle of 360°. Each LED (10) has a maximal deflection angle of light, which is 120°. Since the LEDs are not placed at the same physical spot, there will always be an unlit zone (S) between adjacent LEDs. In spite of the fact that the uniform illumination is speculated in the above-referenced publications, there is still an unlit zone (S), which is formed between light beams (14) of adjacent LEDs (10) positioned between screens (13). These unlit zones (S) are formed because of the spatial design constraints and geometrical considerations. Although, the aforementioned references allegedly maintain that such specific triangular arrangement of the LEDs, without using any optical lenses, is capable of producing the full illumination area of almost 360°, Fig. 4 clearly shows that in reality it is not so. The construction, which is shown in Fig. 4 does not use optical lenses and hence, cannot evenly distribute light on screens (13).

In addition, although LED (10) shown in Fig. 4 is able to distribute light over 120°, light intensity strongly varies with the deflection angle, wherein at the edges, it is significantly lower than in the centre, as shown in Fig. 5A. Thus, in order to achieve a relatively uniform light distribution and wider deflection angle, as shown in Fig. 5B, it is absolutely necessary to compensate for lower luminosity at the edges. This can be achieved by expanding the deflection angle of light emitted by the LEDs using lenses, and thereby, creating light overlapping zones (H) on the screens or on any illuminated surface, according to embodiments of the present invention. The advantages of applying lenses can be seen by comparison of the radiation pattern (light flux) for two models: with and without lenses. Reference is now made to the light flux diagrams for these two models : without lenses (Fig. 6A) and with lenses (Fig. 6B). It can be clearly seen that in the model without lenses (Fig. 6A), the light distribution is greatly uneven, with sharp falls in light intensity below 60% in the following zones: 35°-85°, 150°-220° and 270-330°. In total, these zones of low light intensity constitute approximately 50% of the illuminated area. Moreover, deviations of light intensity in this model (without lenses) are essentially large. As seen in Fig. 6A, light intensity reaches only 20% of relative luminosity in the lowest points.

In the model with lenses, the light distribution is significantly better, with only minor falls in light intensity below 60% in the following zones: 55°- 65°, 85°-95°, 175°-185°, 265°-275°, 295°-305°. In total, these zones of lower light intensity constitute approximately 10%- 15% of the illuminated area. In this model (with lenses), the deviations of light intensity are essentially smaller. As seen in Fig. 6B, light intensity reaches approximately 50% in the lowest points. The light distribution angle of a single LED in the illumination device of the present invention can be as wide as 160°.

Using a larger number of LED strips may simplify the design of the illumination device. In such illumination devices having more than three LED substrates, the form of the optical tube, substrates and contacts may be different from the triangular arrangement. In cases when many substrates are used, the optically transparent tube can be used even without concave surfaces (i.e., without lenses). Although such design has an advantage of the technologically simplified form of the tube, it has essential disadvantages of (a) lower control over the light distribution, since the illuminated areas with light overlapping (H) are larger, and light intensity in those areas might be higher than in other areas; and (b) more complex holder construction is required in order to fix the inner lamp mechanism into a smooth round tube casing.

Another aspect of the present invention is use of the illumination device in any indoor and outdoor illumination applications, for example two-sided illuminated light boxes in street signs, advertising stands, and the like, providing uniform light coverage over each screen.

While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.