WO2003060580A1

WO2003060580A1 - An illuminated device

Info

Publication number: WO2003060580A1
Application number: PCT/GB2003/000110
Authority: WO
Inventors: Morton Graham; Udo Fischer
Original assignee: Morton Graham; Udo Fischer
Priority date: 2002-01-15
Filing date: 2003-01-15
Publication date: 2003-07-24
Also published as: AU2003235638A1; GB0200776D0

Abstract

An illuminated device comprising a rod (10) of an optically transparent material with light source (11) located at least at one end of the rod thus to transmit light into the rod for total reflection therewithin, and a linear reflector (12) extending longitudinally of the rod at a position thereon to reflect light transmitted through the rod and to create a beam of such reflected light emitted from the outer surface of the rod in a transverse direction. Such devices may be used for signage and produce a linear beam of considerable brilliance and colour from a low-power light source such as one or more LED's.

Description

AN ILLUMINATED DEVICE

THIS INVENTION concerns illuminated devices such as may

be used for display purposes to produce an apparent linear beam of light,

usually, but not necessarily, coloured, from a transparent rod to the end

of which is applied a light source.

So called side-emitting illuminated devices are known, for

example, from US 2002/0080623 where light is uniformly distributed

throughout the length of a light transmitting transparent rod usually, but

not necessarily, of an acrylic or other material having similar optical

qualities which permit total internal reflection of the light throughout the

length of the rod, and outcoupling material affixed to an outer surface of

the rod such that light entering the rod at one end travels along the rod by

total internal reflection and the outcoupling material reflects the light

outwardly from the surface of the rod in a transverse direction.

Whilst such devices are generally known, the brilliance of

the outcoupled light beam has certain limitations, particularly if the light

source is a light emitting diode (LED), the total luminance of the light

being limited by the effectiveness of the light source and by the spectral

reflection property of the outcoupling material. If the light source is applied to just one end of the rod then,

in order to ensure uniformity of the transmitted beam throughout the

length of the rod it is necessary to provide a reflector at the opposed end

of the rod to prevent light from escaping at the end.

It is an object of the present invention to provide an

illuminated device of this general kind whose brilliance and optical

performance is improved.

In a typical example of the application of such a device it

may be required to emit a linear beam of light over a vertical span of some

50 degrees where the top of the beam is arranged to be substantially

horizontal with the bottom of the beam defined as 50 degrees below the

horizontal. Lengths of such a rod may be arranged for example around the

canopy of a filling station so that the beam of light can be seen from a

distance as the viewer approaches the station but upon exit from the beam

i.e. beneath 50 degrees below the horizontal the rod then appears as a

clear rod with no light visible. By concentrating the beam in such a

narrow angle a substantially reduced power input is required when

compared with a rod whose entire surface is to be illuminated. Other

advantages ensue from a concentrated beam, for example there is no

wasted light exiting in a direction where it cannot be viewed such as

towards the sky. The device uses the principle of total internal reflection of

light within a clear material showing a negligible absorption in the visible

range of wavelengths. For this reason the surface of the rod must be as

smooth as possible. A preferred material for the rod is clear extruded

PMMA, but certain types of glass can be used instead. The total internal

reflection is interrupted only if the light falls upon an imperfection in the

surface of the rod or a linear reflector placed along the external surface or

as a central core therewithin.

If the rod is of circular cross section it serves as a lens to

amplify the beam width. However, the rod may be of other cross-section

such as square, triangular, ovoid or any other shape. The shape of the

rod, together with the width of the reflector strip will determine the shape

and width of the emitted light beam.

An illuminated device according to the invention, comprises

a rod of an optically transparent material; a light source located at least

at one end of the rod; and a linear reflector extending longitudinally of the

rod and positioned thereon to reflect light transmitted through the rod

from the light source and to create a beam of such reflected light emitted

from the outer surface of the rod in a transverse direction such that the

beam width is directly proportional to the width of the reflector;

characterised in that the spectral reflection factor of the material of the reflector is at least substantially as great as the bandwidth of the light

emitted by the light source.

An embodiment of the invention will now be described, by

way of example only, with reference to the accompanying drawings, in

which :-

Fig. 1 illustrates in transverse cross-section and

illuminated device according to one embodiment of the

invention;

Fig. 2 is an isometric view of the device;

Fig. 3 is a view similar to Fig. 1 of a second embodiment;

and Fig. 4 illustrates a waterproof end cap for use in connection

with the invention.

Referring now to the drawings, a clear acrylic or other

plastic or glass rod 10 typically one metre in length and in the region of

30mm in diameter includes, preferably at both ends, an indentation 11 for

receiving a light source preferably in the form of an LED. Disposed along the length of the rod is a strip 12 of a

material such as paint or tape which, as will be described, serves as a

reflector.

Located within the indentation 11 , in this example, is a

single LED mounted on a printed circuit board (not shown) which may be

contained within a waterproof cap 17 (Fig. 4) in a central region of which

there is a waterproof strain relief bush 18 through which a power supply

cable may pass to the circuit board.

When the LED is illuminated, light is reflected totally within

the rod and if the opposed end thereof has another such light source or a

reflective surface, then without the presence of the reflector strip 12 the

light would be contained within the material of the road but would be

invisible, but for imperfections in the rod, when viewed transversely.

By placing the reflector strip 12 on the circumference of the

rod, light is reflected by it to produce a beam visible on the opposite side

of the rod, the beam width being determined by the proportion of the

circumference of the rod occupied by the reflector strip 12. For example,

if the strip 12 occupies 10 degrees of the circumference of the rod then a

beam of 21.6 degrees will exit opposite the reflector. If the reflector strip

is 20 degrees of the circumference then a beam of 31.6 will be emitted so that the width of the visible beam is determined by the width of the

reflector strip.

Referring now to Fig. 3, in another embodiment, the single

LED is replaced by a uniformly spaced array of nine LED's again disposed

upon a printed circuit board contained within the waterproof end cap.

Such an arrangement provides more evenly distributed light transmission

into and through the rod.

Several such rods may be axially aligned thus to provide the

appearance of a continuous illuminated rod.

While the light source may be other than one or more LED's,

nevertheless LED technology with its durability, zero maintenance and low

power consumption provides considerable advantage thus to produce a

low cost product specifically applicable to the highlighting of buildings,

signage and other forms of commercial illumination. By selecting the light

source of an appropriate colour or a multiple of colours the desired effect

is readily achieved.

The reflector strip may be applied to the rod by co-extrusion

therewith or by casting or screen printing rather than simply bonding a

strip to the surface. It is known that LED's emit a relatively narrow bandwidth

of wavelength such that they can produce extremely pure colour.

Reflecting materials may have a wide bandwidth of spectral

reflection whereas the bandwidth of light emitted by an LED is quite

limited. Therefore, to achieve maximum luminance from the beam of light

produced, the spectral reflection factor of the reflecting material, whether

it be lacquer, paint, film, etc. must be as high as possible in the range of

wavelengths of the LED's. The spectral reflection factor of the reflecting

material must be substantially as great as the bandwidth of the LED, and

preferably slightly greater so that all of the emitted light is reflected.

Similarly, the material must absorb as little as possible and be highly

reflective optically to the light submitted to it. Thus, the spectral reflection

factor of the material of the reflector is matched to the light emitted by the

light source.

Bandwidths vary from one colour to another. For example,

in the visible range of 380nM to 780nM, blue light is emitted in the region

of 428nM while red light is emitted in the region of 645nM.

Preferably, an additional dense white, highly reflective outer

covering layer should be placed upon the reflective material on its outer

surface thus to avoid or minimise any transmission of losses through the reflective material in a direction opposite to that in which the beam is to

be transmitted.

When the reflector is matched to the light source and thus

shows as a coloured line, then this line will appear illuminated even

during the daytime by reflecting daylight through the rod as the collecting

lens thus to show the desired colour during daytime at least where the

strip is visible as a result of the lens effect.

Multiple coloured LED's may be used to provide a mix, for

example, purple from red and blue.

The luminance and efficiency of the device can be improved

by using a reflector of a fluorescent material which converts the radiation

from the shorter wavelength of daylight into radiation of the desired

colour/ wavelength region in addition to the expected reflected radiation.

In this case, the fluorescent reflector is covered on its outer surface as

referred to previously.

When LED's are used as the light source, it is preferable to

use those with concentrating spherical lenses thus to produce a narrow

beam illumination to overcome any tendency for there to be a luminance

gradient along the rod. In certain prior art documents this gradient is overcome by modulating the reflector characteristics along the length of

the rod.

To provide light sources at both ends of the rod reduces the

visible impression of non-uniformity enabling a longer length of rod to be

uniformly illuminated.

In a further embodiment, a wider angle of visible beam may

be provided by using a T-shaped reflector profile where the leg of the T is

disposed radially towards the centre of the rod while the top of the T is a

bonded reflector of a similar width to that of the radius leg, the reflector

being located at the outer surface of the rod. Such a reflector may be co-

extruded with the rod during manufacture.

In a still further embodiment, the rod may contain a central

axial core of an opaque material which serves as a central reflector

providing 360 degrees of surface illumination. In this case, a plurality of

LED or other light sources are arranged in a circular formation around the

central core on one or both ends of the rod.

Whatever light source is used, any parts of the end surfaces

of the rods not occupied by the light sources themselves should preferably be coated with a reflective material thus to ensure no light loss through

the ends of the rod.

It is preferable that the material of the rod be produced by

extrusion rather than casting since a cast rod will require a polished

surface finish resulting in a multitude of microscopic scratches thus

allowing light to exit the rod other than at the intended beam location and

thus the rod would appear less than clear.

Claims

1. An illuminated device comprising a rod of an optically transparent

material; a light source located at least at one end of the rod; and

a linear reflector extending longitudinally of the rod and positioned

thereon to reflect light transmitted through the rod from the light

source and to create a beam of such reflected light emitted from

the outer surface of the rod in a transverse direction such that the

beam width is directly proportional to the width of the reflector;

characterised in that the spectral reflection factor of the material

of the reflector is at least substantially as great as the bandwidth

of the light emitted by the light source.

2. An illuminated device according to Claim 1, wherein the spectral

reflection factor of the material of the reflector is greater than the

bandwidth of the light emitted by the light source.

3. An illuminated device according to Claim 1 or Claim 2, wherein the

cross-sectional profile of the rod is circular.

4. An illuminated device according to Claim 1 or Claim 2, wherein the

cross-sectional profile of the rod is non-circular.

5. An illuminated device according to any preceding claim, wherein

the light source is a plurality of light emitting diodes.

6. An illuminated device according to any preceding claim, wherein

the light source is located at both ends of the rod.

7. An illuminated device according to any preceding claim, wherein

the rod is of clear acrylic.

8. An illuminated device according to any of Claims 1 to 7, wherein

the rod is of clear polycarbonate.

9. An illuminated device according to any preceding claim, wherein

the linear reflector is painted on the outer surface of the rod.

10. An illuminated device according to any of Claims 1 to 9, wherein

the linear reflector is provided in the form of a tape bonded to the

outer surface of the rod.

11. An illuminated device according to any of Claims 1 to 9, wherein

the linear reflector is formed along the surface of the rod by co-

extrusion therewith.

12. An illuminated device according to any of Claims 1 to 9, wherein

the linear reflector is of T-shaped cross-section with the leg of the

T being disposed radially with respect to the rod and the top of the

T being bonded to the outer surface thereof around at least a part

of the circumference thereof.

13. An illuminated device according to any of Claims 1 to 9, wherein

the linear reflector is a core of an opaque material which passes

longitudinally through the rod internally thereof thus to reflect

light with a beam providing illumination throughout a substantial

proportion of the circumference of the rod.

14. An illuminated device according to any preceding claim, comprising

a plurality of such rods axially aligned end-to-end respectively.