NZ510592A

NZ510592A - LED traffic signal with anti-reflection mask

Info

Publication number: NZ510592A
Application number: NZ51059201A
Authority: NZ
Inventors: Keith James Aldridge; Raj Nath Bhat
Original assignee: Aldridge Traffic Systems
Priority date: 2000-10-31
Filing date: 2001-03-20
Publication date: 2001-06-29
Also published as: AU737997B3

Abstract

In a traffic light, light emitting diodes 24 project from the front of the printed circuit board 18 on which they are mounted and through the apertures 28 in a non-reflective mask 14 covering the front of the board. The mask allows the light from the diodes to be seen but prevents the reflection of sunlight from the other parts of the front of the circuit board.

Description

Patent Form No 5.

NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION 510 5 9 2 IMPROVEMENTS IN TRAFFIC SIGNALS We Aldridge Traffic Systems Pty Limited, an Australian company of 14 Leeds Street, Rhodes, New South Wales, 2138, Australia HEREBY declare the invention, for which we pray that a patent be granted to us and the method by which it is to be performed, to be described in and by the following statement:- intellectual property office of n.z. 2 0 MAR 2001 Received The present invention relates to improvements in traffic signals and, in particular, to a non-reflective traffic signal in which illumination is provided by a plurality of light emitting diodes (LED's).

LED traffic signals are a fairly recent development that are gradually replacing the more traditional globe traffic signals. Although the use of LED's has many advantages over the use of globes in traffic signals, some problems remain. For instance, LED traffic signals utilizing a clear front lens may result in a "veiling reflection" effect, causing reflected sunlight to be white. The reflected white light could, in some circumstances, be of such an intensity that it appears as an undefined signal causing confusion to drivers approaching the traffic signal. Furthermore, the reflected white light will add to the aspect signal when the aspect (either red, amber or green) is on, causing desaturation of the colour of the aspect signal.

Therefore, the effect of "veiling reflection" on LED traffic signals can cause the colour of the signal to move outside the allowable range of colour for that signal. To some extent, "veiling reflection" can be prevented or made less likely by the use of a coloured front lens (or cover) designed to maintain the colour of the signal within the allowable range under the conditions presently used in the art for measuring "sun phantom" intensity.

However, the use of coloured front lenses may lead to the creation of a "sun phantom" effect, because any reflected sunlight from the lens will be coloured and so the traffic signal will appear to be on when it is off.

One of the major causes of reflected sunlight from an LED traffic signal is the LED printed circuit board itself, from the anterior (or front) side of which project a plurality of generally evenly distributed LED's and which also supports reflective elements such as resistors, transistors, current diodes and printing. Each of these elements of the board are, in themselves, reflective to a minor extent, but their combined effect is to create a generally reflective surface, the undesirable consequences of which are as described above.

It is an object of the present invention to overcome, or at least substantially ameliorate, the disadvantages and shortcomings of the prior art.

According to the present invention, there is provided a traffic signal in which illumination is provided by a plurality of light emitting diodes projecting from an anterior side of a printed circuit board on which the diodes are mounted, characterised in that the traffic signal includes a non-light reflective mask covering the anterior side of the board and having a plurality of apertures at locations corresponding to the location of the plurality of light emitting diodes for allowing the diodes to project through the apertures but masking the remainder of the anterior side of the board to prevent reflection of sunlight therefrom.

Preferably, the non-light reflective mask has a matt black colour.

It is preferred that the mask is made of a polypropylene copolymer.

In order that the invention may be readily understood and put into practical effect, reference will be made to the accompanying drawings, in which: Fig 1 is an exploded perspective view of a traffic signal according to a preferred embodiment of the present invention, Fig 1A is an enlarged view of detail A shown in Fig 1, Fig 2 is a front elevational view of the non-light reflective mask used in the traffic signal of Fig 1, and Fig 3 is a cross sectional view through a cut-away portion of the traffic signal shown in Fig 1.

The traffic signal 10 shown in Fig 1 has a board assembly 12, a non-light reflective mask 14, and a plurality of screws 16 for securing the correctly positioned mask 14 to the board assembly 12.

The board assembly 12 consists of a printed circuit board 18 mounted to a circumferentially surrounding bracket 20 from which extend mounting members 22 for locating the traffic signal 10 to a traffic signal lantern box or the like enclosure.

The posterior (or rear) side of the board 18 has mounted thereto the essential electronic componentry (not shown) for operating the plurality of light emitting diodes 24 which project from the anterior side of the board 18 in a generally even distribution. There are a plurality of reflective elements 26, such as transistors, resistors and current diodes, supported on the anterior side of the board 18 which, together with any white printing that might be displayed on the anterior side of the board 18, combine to create a generally reflective surface.

The mask 14, which, in this embodiment, has a matt black colour and is made of a polypropylene copolymer, has a plurality of apertures 28 at locations corresponding to the location of the plurality of light emitting diodes 24, and when the mask 14 is being correctly positioned over the anterior side of the board 18, each of the light emitting diodes 24 pass through respective apertures 28 of the masks 14 so that they project through the apertures 28, but the remainder of the anterior side of the board 18 is masked or covered to prevent reflection of sunlight therefrom. Once correctly positioned, the mask 14 is secured to the board assembly 12 by the application of screws 16 through overlying holes 30, 32 in respective peripheral regions of the mask 14 and board 18.

The traffic signal of the present invention has been found to prevent the creation of "sun phantom" effect when coloured front lenses (or covers) are used. For instance, in a test conducted by a NATA accredited laboratory, the "sun phantom" intensity measurements (in units of candelas (cd)) of a traffic signal having a green LED signal with two samples of green coloured front lenses were 38.0 cd and 47.6 cd respectively, both of which measurements represent a fail mark in relation to accepted standards in the art for avoidance of "sun phantom". When tests were conducted under the same conditions but with the use of a mask as described above as part of the traffic signal, the "sun phantom" intensity measurements of the traffic signal were 15.1 cd and 19.0 cd respectively, both of which measurements represent a pass mark in relation to the aforementioned standards. In fact, the reduction in "sun phantom" intensity for the green signal is in the order of about 60% when the traffic signal of the present invention is used as compared to prior art LED traffic signals.

A particularly preferred polypropylene copolymer is that marketed under the name HOSTALEN PPT 2052 by Hoechst.

Various modifications may be made in details of design and construction without departing from the scope and ambit of the invention. 6

Claims

WHAT WE CLAIM IS:

1. A traffic signal in which illumination is provided by a plurality of light emitting diodes projecting from an anterior side of a printed circuit board on which the diodes are mounted, characterised in that the traffic signal includes a non-light reflective mask covering the anterior side of the board and having a plurality of apertures at locations corresponding to the location of the plurality of light emitting diodes for allowing the diodes to project through the apertures but masking the remainder of the anterior side of the board to prevent reflection of sunlight therefrom.

2. The traffic signal of claim 1 wherein the non-light reflective mask has a matt black colour.

3. The traffic signal of claim 1 or claim 2 wherein the mask is made of a polypropylene copolymer. Dated this 15th day of March, 2000 Aldridge Traffic Systems Pty Limited Patent Attorneys for the Applicant PETER MAXWELL & ASSOCIATES intellectual property office of N.z 2 o MAR 2001 received