AU2006203081A1 - An improved yellow traffic signal light device - Google Patents

Description

Regulation 3.2 Revised 2/98

AUSTRALIA

Patents Act, 1990

ORIGINAL

COMPLETE SPECIFICATION TO BE COMPLETED BY THE APPLICANT NAME OF APPLICANT: ACTUAL INVENTOR: ADDRESS FOR SERVICE: Aldridge Traffic Systems Pty Limited (ACN 001 678 557) Andrew Bull Peter Maxwell and Associates Level 6 Pitt Street SYDNEY NSW 2000 AN IMPROVED YELLOW TRAFFIC SIGNAL LIGHT DEVICE 2005 903 750 14 July 2005 Australia INVENTION TITLE: DETAILS OF ASSOCIATED PROVISIONAL APPLICATION NO: The following statement is a full description of this invention including the best method of performing it known to us:m:\docs\20061037\102892.doc The present invention relates to an improved yellow traffic signal light device.

Incandescent reflector lamps have traditionally been used in traffic 0 signal lights, but with the emergence of light emitting diode (LED) technologies,

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LEDs are increasingly being used for this purpose.

Red, orange and yellow (also referred to as amber) LEDs commonly use 0aluminium indium gallium phosphide (AllnGaP) dye technology to produce their respective colours, whereas green and blue LEDs commonly use indium gallium nitride (InGaN) dye technology to produce their respective colours.

These technologies have, over time, displaced older gallium arsenide phosphide (GaAsP), gallium phosphide (GaP), and aluminium gallium arsenide (AIGas) LED dye technologies.

Manufacturers commonly test and sort in an appropriate bin each LED according to luminous intensity and colour. Like incandescent reflector lamps, the luminous intensity of LED devices is specified in terms of its beam angle.

However, LED manufacturers refer to this as the viewing cone angle or the 29 2 angle (in degrees). Typically, all LEDs within a bin do not vary in luminous intensity by more than a factor of two. Because of the difficulty in measuring luminous intensity accurately, there is an expected 10% overlap between adjacent bins.

The colour of an LED device is specified in terms of the dominant wavelength emitted Xd (in nanometres). AllnGaP LEDs produce the colours red (626 to 630nm), red-orange (615 to 621 nm), orange (605nm), and yellow (590-592nm). InGaN LEDs produce the colours green (525nm), blue green (498 to 505nm), and blue (470nm).

The luminous intensity, colour and forward voltage of AIInGaP LEDs are affected by the temperature of the LED p-n junction. As the temperature of the 14/07/06 AIInGaP LED p-n junction increases, the luminous intensity decreases, the _dominant wavelength shifts towards longer wavelengths and the forward voltage drops. In contrast, the variation in luminous intensity in InGaN LEDs 00with operating ambient temperatures is small (about 10%) from 200C to 800C.

0 The small variations are not readily visible and need not be taken into account \ffor most applications. However, the dominant wavelength of InGaN LEDs does vary with LED drive current. As the LED drive current increases, the dominant wavelength moves towards shorter wavelengths.

Therefore, AIInGaP LEDs (by virtue of their dye technology) are significantly more temperature sensitive than InGaN LEDs. This heightened sensitivity to temperature makes it particularly difficult for manufacturers to produce commercially viable amounts of yellow LEDs which, according to the Australian Standard for colour boundaries for a yellow traffic signal (AS 2144- 2002), must be in the chromaticity range of 585-590nm. Temperature variations during the manufacturing process may cause the desired chromaticity range of a yellow LED to shift to outside the allowable boundary set by the Australian Standard.

It has now been found by the present inventors that a yellow traffic signal light having the required chromaticity range of 585-590nm may be provided by using InGaN dye technology to produce warm white coloured LEDs (rather than the conventional green, blue green, and blue coloured LEDs) having a sufficient luminous intensity that, when combined with a suitable yellow coloured lens, results in yellow light in the required chromaticity range. The use of InGaN dye technology for this purpose means that the manufacture of the LED component of yellow traffic signal lights of the present invention is no longer as temperature sensitive as in the prior art and so no longer relies on the difficult production of commercially viable amounts of 14/07/06 yellow LEDs. It has also been found by the present inventors that the yellow coloured lens must be of a suitable thickness to facilitate the transmission of the desired yellow colour.

00 According to the present invention, there is provided a yellow traffic 0 signal light device comprising:a plurality of light emitting diodes adapted to emit a warm white coloured light, the light emitting diodes manufactured by a process using indium gallium nitride dye technology, a yellow coloured lens for filtering the light emitted by the light emitting diodes to provide a yellow colour being within a chromaticity range of 585 to 590nmm, and a power supply for applying current to the light emitting diodes.

In order that the invention may be readily understood and put into practical effect, reference will now be made to the following Example of a method for manufacturing a preferred yellow traffic signal light device of the invention.

A plurality of warm white LEDs are manufactured in the conventional manner using InGaN dye technology. The luminous intensity of each such LED is 7,500 mcd. The LEDs are operably incorporated into a traffic signal light in a conventional manner, and a yellow coloured lens is then added to create a traffic signal light device, the emitted light of which is yellow light in the chromaticity range (or wavelength) of 585-590nm. The yellow coloured lens has a thickness of 5mm and has a combination of colour components so mixed to produce a yellow colour having the aforementioned chromaticity range.

A process will now be described for producing the yellow coloured lens which, when located in front of the aforementioned warm white LEDs manufactured using InGaN dye technology as part of a traffic signal light 14/07/06 device, will provide a yellow colour within the chromaticity range of 585 to 590 nm.

Warm white LEDs are selected to have a colour rank of D1, D2 which corresponds to a dye temperature, when the current passes through the LED, of between 3800K 4600K in order to achieve colour co-ordinates of: X 0.3575 Y 0.3610 within the AS 2144-2002 colour boundaries.

Polymethylmethacrylate (PMMA) is the polymer present in the lens and is produced as follows:- 1) Acetone is reacted with hydrogen cyanide to form acetone cyanhydrin

CH

3 CH C O HCN SHydrogen Cyanide

CH

3 CH C

C

CH

3

CH

3 Acetone Cyanhydrin 2) The acetone cyanhydrin is treated with sulphuric acid and methyl alcohol to give methacrylate monomer.

CH3 OH Methyl CH 2 Alcohol C H 2 S0 4

C

CH

3 CN CHi CO.O CH 3 Methyl Methacrylate 14/07/06 The conversion of the monomer to polymer follows essentially the pattern of normal vinyl derivative chain growth, i.e. free radicals are formed and oo unite with inactivated molecules to form long chains which are substantially

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5 unbranched. The overall polymerisation process may be illustrated as follows:-

CH

3

CH

3 CH3 CH 3 I I I CH 2 C CH 2 2 C CH 2

C

CO.OCH

3 CO.OCHs CO.OCH 3

CO.OCH

3 A yellow pigment, namely, non-cadmium pigment, is added in the polymerisation process and, as a result, is compounded with the PMMA molecules. The process is so controlled as to produce granules.

The granules are then heated to a temperature of 2600C to form a sufficiently flowable or molten material for injection moulding. An injection moulding machine fitted with a lens die receives the molten material and the formation of a hardened lens then occurs in the conventional manner.

The hardened lens is then tested to determine if, when located in front of the warm white LEDs manufactured using InGaN dye technology, it produces a yellow colour that is within the chromaticity range of 585 to 590nm.

If not, the mix during polymerisation of monomer with pigment is adjusted so as to achieve the colour as required.

The so produced yellow coloured lens will ensure that there is no veiling reflection.

A basic assembly of a preferred yellow traffic signal light device according to the invention is shown in Fig 1. The device includes a back housing 12, display board 14, lens element 16, and a front housing 18. The 14/07/06 Sdisplay board 14 has a power supply printed circuit board (PCB) 20, an LED PCB 22, an LED display carrier 24, and a plurality of warm white LEDs 26.

The lens element 16 has a gasket 28 and a lens cover 30 of 5mm thickness oo with a compounded yellow colour of the desired mix.

0 Various modifications may be made in details of design and construction \O without departing from the scope and ambit of the invention.

14/07/06

Claims (8)

1. A yellow traffic signal light device comprising:- 00oo a plurality of light emitting diodes adapted to emit a warm white coloured light, the light emitting diodes manufactured by a IND process using indium gallium nitride dye technology, a yellow coloured lens for filtering the light emitted by the light emitting diodes to provide a yellow colour being within a chromaticity range of 585 to 590nmm, and a power supply for applying current to the light emitting diodes.

2. The yellow traffic signal light device of claim 1 wherein the luminous intensity of each light emitting diode is 7,500 mcd.

3. The yellow traffic signal light device of claim 1 or claim 2 and further including a back housing to which a display board is connected, the display board supporting the light emitting diodes.

4. The yellow traffic signal light device of any one of claims 1 to 3 wherein the lens comprises a hemispherically shaped lens element.

The yellow traffic signal light device of any one of claims 1 to 4 and further including a front housing.

6. The yellow traffic signal light device of claim 3 wherein the display board includes a power supply printed circuit board and a printed circuit board for the light emitting diodes. 14/07/06 O 9 O

7. The yellow traffic signal light device of any one of claims 1 to 6 wherein the lens is made of polymethylmethacrylate compounded with a yellow, non- oo cadmium payment. O ci \O

8. A yellow traffic signal light device substantially as hereinbefore 0 described with reference to the accompanying drawings. Dated this 13 day of July 2006 Aldridge Traffic Systems Pty Limited Patent Attorneys for the Applicant PETER MAXWELL AND ASSOCIATES 14/07/06