EP1781985A1

EP1781985A1 - Luminous blongate device with a light fibre and a ight injector

Info

Publication number: EP1781985A1
Application number: EP05725629A
Authority: EP
Inventors: Marcella M. Pesenti
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2004-04-16
Filing date: 2005-03-14
Publication date: 2007-05-09
Also published as: JP2007533102A; WO2005106322A1

Abstract

This luminous elongate device (10) comprises - aligned along a longitudinal axis (X) - a light fibre (20) and at least a light injector (30), including a light source (40) and a coupling assembly (50) connecting the light source (40) to the light fibre (20). The device (10) is characterised in that the light source (40) comprises a single LED (41) and the coupling assembly (50) comprises a funnel shaped reflective screen (54) with its narrower end (541) mounted around the LED (41) and its wider end (542) open towards the light fibre (20). The manufacture of relatively long luminous devices (10) is possible, with very low power consumption.

Description

LUMINOUS ELONGATE DEVICE WITH A LIGHT FIBRE AND A LIGHT INJECTOR

DESCRIPTION

Field

The present invention relates to a luminous elongate device, i.e. to an elongate device that emits a limited amount of light in every direction, sufficient to be easily seen but substantially insufficient to illuminate the surrounding environment. Such a device is useful particularly for signing and marking of any type, such as road signs, road markings, shop signs, decorative signs, safety signs, and the like.

Background

Most common luminous elongate devices are generally based on fluorescent light tubes, that can be shaped into any desired linear pattern and can exhibit any desired colour.

More recently, devices of this kind are also known, that are based on a light guide such as a low cost light fibre, particularly a large core plastic light fibre, adapted to transport light over the wavelength range of visible light. Plastic light fibres can be shaped rather easily and can exhibit any desired colour, if coupled to a corresponding light source. In addition, they feature a much stronger structure than fluorescent tubes as well as a better ability to withstand difficult environmental conditions. On the other hand, these devices are more expensive and energy consuming . Summary of the Invention

The present invention provides a low cost fibre type luminous elongate device.

This is achieved by a device according to claim 1; preferred optional features are set forth in dependent claims.

A luminous elongate device of the invention comprises - aligned along a longitudinal axis - the input end of a light fibre and at least a light injector, including a light source and a coupling assembly connecting the light source to the light fibre, characterised in that the light source comprises a single LED (light emitting diode) and the coupling assembly comprises a funnel shaped reflective screen with its narrower end mounted around the LED and its wider end open towards the light fibre. A LED is a cheap and energy saving light source, that has been found to be suitable to provide light for a fibre of a luminous elongate device if emitted light is collected and deflected by means of the reflective screen placed right onto the head of the LED, even in case the power of the LED is as low as 1 .

It is to be noted that, although the device has a rectilinear longitudinal axis within the coupling assembly, out of the coupling assembly the longitudinal axis follows the fibre and any bend thereof.

In principle, the light fibre can be of any type. However, in an embodiment preferred for its low cost, the light fibre is a large core plastic fibre adapted to transport light over the wavelength range of visible light. A fibre of this type is any of the fibres available under the trade name "3M HL High Luminance Light Fibre" from 3M, St. Paul, MM, USA, e.g. the LF120HL fibre or the LF70HL fibre.

The reflective screen is substantially concave, and preferably has the shape of a paraboloid, i.e. a solid generated by revolution of a parabola around an axis coincident with the axis of the luminous elongate device. The parabolic shape allows better control of the deflection of the light beams emitted by the LED.

Preferably, the wider end of the reflective screen has a diameter that is 1.3 to 3 times, and most preferably about 2 times, the diameter of the narrower end; again preferably, the length of the reflector along the axis of the luminous elongate device is 1.0 to 2.5 times, and most preferably about 1.7 times, the diameter of the narrower end.

Whatever the exact geometric shape of the reflecting screen, its shape and dimensions are such that light beams emitted by the LED and reflected by the reflective screen form an angle with the axis of the luminous elongate device that is not greater than, and preferably about equal to a predetermined angle, that depends on the fibre that is used. When a fibre of the above cited type 3M High Luminance Light Fibre is used, the predetermined angle is 8°. Indeed, light beams entering the fibre at angles substantially smaller than such predetermined angle are transmitted into the fibre and can continue to travel therein with only a minimum portion of the light being scattered out of the fibre.

Preferably, the reflective screen is made of a thin metal sheet, such as aluminium. Aluminium indeed can exhibit a very high surface reflectivity, and is relatively easy to machine into the desired shape. Other suitable materials for the reflective surface of the screen include metallized polymeric films, and non-metallized polymeric films having high reflectivity. An exemplary metallized polymeric films is an aluminium vapor-coated polyester film. An exemplary non-metallized polymeric film is Vikuiti™ ESR (Enhanced Specular Reflector) obtainable from 3M, St. Paul, MN, USA. Preferably the reflective surface of the screen reflects greater than 80% of the incident light, more preferably greater than 90%, and most preferably greater than about 95% of the incident light. Clearly, if a reflective film is used, such film is applied onto a suitable support.

Preferably, the coupling assembly comprises: a hollow main body with an inner cylindrical cavity, the LED being provided in the cavity, supported in the centre of a base of said cavity, a ring-like bushing, having an external cylindrical side matching the cylindrical cavity and an internal conical side to engage the wider end of the reflective screen; pressure means to urge the bushing toward the base of the cavity, thus holding the reflective screen around the LED.

More preferably, the pressure means comprise a sleeve body of the coupling assembly, in screwing engagement in the cylindrical cavity of the main body, and pressing against the bushing.

This simple structure allows for easy, precise and stable positioning of the reflective screen. More preferably, thanks to its structure, the coupling assembly is easily made water tight, so as to ensure better working conditions over time in outdoor applications, or in applications under aggressive environmental conditions.

Preferably, the coupling assembly comprises heat dissipation means, to dissipate heat generated by the LED and ensure better working conditions thereto. Such means can preferably comprise a finned portion of the main body, adjacent said base of the cavity of the main body. In this way, enough heat is dissipated with a simple and solid structure.

For relatively short fibres, the luminous elongate device of the invention comprises only one light injector at one end of the fibre, and thus only one light source and one coupling assembly. If the fibre is longer, the luminous elongate device preferably comprises two light injectors, one at each end of the light fibre, whereby the device has a more uniform luminosity.

Brief Description of the Drawings

Further features and advantages of the invention will become apparent from the following description of a preferred embodiment thereof, given by way of example and with reference to the enclosed drawings . In the drawings : figure 1 is a schematic view of a luminous elongate device of the invention; figure 2 is a detail perspective view of part of the device of figure 1, showing a coupling assembly; figure 3 is a longitudinal sectional view of the coupling assembly of figure 2, with partially separated parts; figure 4 is a perspective view of the coupling assembly of figure 3 ; figure 5 is a perspective view of the reflective screen of the coupling assembly of figures 2 to 4; figure 6 shows a schematic detail of a longitudinal sectional view of the coupling assembly of figures 2 to 4.

Detailed Description

In fig. 1 of the drawings, a luminous elongate device 10 is shown, that comprises a large core plastic light fibre 20, having a large core 21 covered by a thin cladding 22 (see fig. 2) . An example of a suitable fibre 20 is a LF120HL 3M High Luminance Light Fibre, available from 3M, St. Paul, MN, USA, which fibre has a 12 mm diameter core 21 covered by a 1 mm thick cladding 22, resulting in an overall diameter of about 14 mm. The refractive index of the cladding 22 is lower than the refractive index of the core 21, so that the structure is able to perform as a light fibre, keeping within the core 21 the light beams that hit the cladding 22 at an angle lower than a predetermined angle α. The fibre 20 is 5 to 10 m long, and is flexible enough to be shaped rather freely according to the desired arrangement or sign; figure 1 shows - just as an example - a simple arrangement

(useful to highlight the outline of a door in a building) , it being clear that not only other linear signs can be made with a device according to the invention, but also that several devices of the invention may be used together to make more complex signs. Of course, as with all light fibres, care must be taken to ensure that bent radiuses are large enough to ensure that the optical properties of the fibre are retained.

At each of the two ends of the fibre 20, the device 10 is provided with a light injector 30, that includes a light source 40 and a coupling assembly 50 (see figs. 2 to 4) . The coupling assembly 50 has a main body, 51, that is substantially hollow, having an internal cylindrical cavity 512 and a substantially circular base 513.

The light source 40 includes a single, low power, LED 41, mounted in the centre of the base 513, and having its light emitting head 411 faced into the cavity 512 and an electric supply cable 42 that exits the main body 51, protected by a cable protection sleeve 53, coupled to the main body 51. To ensure an effective seal between the main body 51 and the sleeve 53, these are provided with matching threads, respectively numbered 514 and 534 in the drawings, and an o- ring gasket 52 is mounted therebetween. To ensure an effective seal between the sleeve 53 and the cable 42, the sleeve 53 is provided with a conical rubber gasket 531, pressed by a ring cap 532 that is screw engaged onto the sleeve 53; when the cap 532 is screwed onto the sleeve 53, its internal conical shape urges the conical rubber gasket 531 against the cable 42, holding and sealing it with respect to the light injector 30. The main body 51 is provided with annular fins 515, formed around the zone of the body 51 where the LED 41 and its supply cable 42 are mounted, so as to dissipate heat generated by these elements.

In the cavity 512, a reflective screen 54 is mounted onto and around the LED 41, particularly around its light emitting head 411. The reflective screen 54 is funnel shaped, having an narrower open end 541 and a wider open end 542. This reflective screen 54 has the shape of a solid generated by revolution of a section of a parabola around the axis X, in particular the shape of a section of a paraboloid having X as axis. The screen 54 is made by a thin sheet of reflective metal, such as aluminium.

The wider end 542 of the reflective screen has a diameter that is 1.3 to 3 times, preferably about 2 times, the diameter of the narrower end 541, and the length of the reflector along the axis X is 1.0 to 2.5 times, preferably about 1.7 times, the diameter of the narrower end.

The reflective screen 54 is firmly but delicately held in position within the cavity 512 by a ring-like bushing 55, that has an external cylindrical side 551 matching the cylindrical cavity 512 and an internal conical side 552 that engages the wider end 542 of the reflective screen 54 and presses the screen 54 against the head 411 of the LED 41. To ensure that the pressing action is actually as delicate as required by the thin structure of the reflective screen 54, the bushing 55 is made with an exact axial length, so that it abuts against the base 513 when fully pressed.

The coupling assembly 50 includes also a sleeve body 56, intended to press the bushing 55 against the reflective screen 54, and to keep the fibre 20, transversely cut at a right angle, held against the outer end face of the bushing 55. To ensure the pressing action onto the bushing 55 and also an effective seal between the main body 51 and the sleeve body 56, these latter are provided with matching threads, respectively numbered 516 and 566 in the drawings, and an o- ring gasket 57 is mounted therebetween. Therefore, the sleeve body 56 acts as pressure means for the bushing 55.

To ensure that the fibre 20 is effectively gripped by the sleeve body 56 and also ensure an effective seal between the sleeve body 56 and the fibre 20, the sleeve body 56 is provided with a conical rubber gasket 561, pressed by a ring cap 562 that is screw engaged onto the sleeve body 56. When the cap 562 is screwed onto the sleeve body 56, its internal conical shape urges the conical rubber gasket 561 against the fibre 20, gripping the fibre with respect to the light injector 30, and holding it in abutment against the bushing 55; gasket 561 ensures also sealing between the fibre 20 and the light injector 30.

As shown schematically in figure 6, the light beams B emitted by the head 411 of the LED 41 hit the reflective screen 54, and are reflected toward the fibre 20 with an angle α with respect to axis X. The shape of the reflective screen 54 is such as to keep the angle as close as possible to 8°, since - when the fibre 20 is of the type mentioned above - this is the angle that ensures that the light beams B - once entered the fibre 20 - do not exit therefrom as soon as they are incident on the cladding 22 but, rather, can undergo multiple internal reflections at the cladding 22 before they exit the fibre 20; in this way, all the light emitted by the LED 41 is efficiently injected into the fibre 20, and is thus available for making the fibre 20 a luminous object. An angle α greater than 8° would have the consequence that the light beams would exit the fibre 20 the first time they are incident on the cladding 22; on the other hand, the smaller the angle . is, the more difficult is the actual construction of the reflective screen 54, as well as its correct positioning while, for an angle α substantially less than 8°, the likelyhood of light being scattered out of the fibre is substantially reduced.

Using the construction described above with reference to the drawings, it is possible to manufacture elongate luminous devices as long as 10 m or even longer, using two simple LEDs, with just 1 W power consumption each (or even a single LED, for short fibre constructions) , and a very cheap and strong large core light fibre. The construction thus makes the practical use of elongate luminous devices possible in many instances where they could not be used previously, for example in road marking.

Claims

1. A luminous elongate device, comprising - aligned along a longitudinal axis (X) - the input end of a light fibre (20) and at least a light injector (30) , including a light source (40) and a coupling assembly (50) connecting the light source (40) to the light fibre (20) , characterised in that the light source (40) comprises a single LED (41) and the coupling assembly (50) comprises a funnel shaped reflective screen (54) with its narrower end (541) mounted around the LED (41) and its wider end (542) open towards the light fibre (20) .

2. The luminous elongate device of claim 1, wherein the reflective screen (54) has the shape of a section of a paraboloid.

3. The luminous elongate device of claim 2 , wherein the wider end (542) of the reflective screen (54) has a diameter that is 1.3 to 3 times the diameter of the narrower end (541), and the length of the reflector (54) along the axis (X) of the luminous elongate device (10) is 1.0 to 2.5 times the diameter of the narrower end (541) .

4. The luminous elongate device of any of claims 1 to 3 , wherein the shape and dimensions of the reflective screen (54) are such that light beams (B) emitted by the LED (41) and reflected by the reflective screen (54) form an angle with the axis (X) of the luminous elongate device (10) that is not greater than a predetermined angle ( ) .

5. The luminous elongate device of claim 4, wherein said predetermined angle (α) is about 8°.

6. The luminous elongate device of any of claims 1 to 5, wherein the reflective screen (54) is made of a thin metal sheet.

7. The luminous elongate device of claim 6, wherein the reflective screen (54) is made of aluminium.

8. The luminous elongate device of any of claims 1 to 5, wherein the reflective screen (54) is made of a reflective film applied onto a suitable support .

9. The luminous elongate device of any of claims 1 to 8, wherein the coupling assembly (50) comprises: -a hollow main body (51) with an inner cylindrical cavity (512), the LED (41) being provided in the cavity (512), supported in the centre of a base (513) of said cavity (512),

-a ring-like bushing (55) , having an external cylindrical side (551) matching the cylindrical cavity (512) and an internal conical side (552) to engage the wider end (542) of the reflective screen (54) ; -pressure means (56) to urge the bushing (55) toward the base (513) of the cavity (512) , thus holding the reflective screen (54) around the LED (41) .

10. The luminous elongate device of claim 9, wherein the pressure means comprise a sleeve body (56) of the coupling assembly (50) , in screwing engagement in the cylindrical cavity (512) of the main body (51) , and pressing against the bushing (55) .

11. The luminous elongate device of any of claims 1 to 10, wherein the coupling assembly (50) is water tight.

12. The luminous elongate device of any of claims 1 to 11, wherein the coupling assembly (50) comprises heat dissipation means (515) , to dissipate heat generated by the LED (41) .

13. The luminous elongate device of claims 9 and 12, wherein the main body (51) has a finned portion (515) , adjacent said base (513) of the cavity (512) thereof.

14. The luminous elongate device of any of claims 1 to 13, wherein the light fibre (20) is a large core plastic light fibre, adapted to transport light over the wavelength range of visible light.

15. The luminous elongate device of claim 14, wherein the fibre (20) is at least 1 m long.

16. The luminous elongate device of claim 15, wherein the fibre (20) is at least 9 m long.

17. The luminous elongate device of any of claims 1 to 16, comprising two light injectors (30) , one at each end of the light fibre (20) .