GB2261981A

GB2261981A - Tritium powered luminescent signs

Info

Publication number: GB2261981A
Application number: GB9125222A
Authority: GB
Inventors: Allan George Kevin Wallace; Ray Yates
Original assignee: ALLPRINT SUPPLIES Ltd
Current assignee: ALLPRINT SUPPLIES Ltd
Priority date: 1991-11-27
Filing date: 1991-11-27
Publication date: 1993-06-02
Also published as: GB9125222D0

Abstract

A tritium powered emergency exit sign is provided comprising an elongated tritium powered light tube 5 mounted at the focus of a parabolic reflector 3 coated with a phosphorescent coating. The tube and reflector are mounted in an elongate trough shaped housing, with a translucent cover 2. In an emergency, e.g. in the event of a power failure in a building or other structure, the phosphorescent coating will reinforce the light emitted by the tritium tube for a short period whilst the eyes adjust to the darkness. <IMAGE>

Description

TRITIUM POWERED LUMINESCENT NT SIGNS This invention relates a tritium powered luminescent signs.

It is known to use tritium powered luminescent signs to indicate emergency exits in buildings, vehicles, mine shafts and galleries etc.

in the event of a power failure. Such luminescent signs are selfpowered, i.e. they comprise a tritium containing light bulb, the inner surface of which is coated with a phosphor which is energised by the radioactive tritium. Tritium bulbs are also used to provide low levels of lighting in photographic dark-rooms etc. The light output from such bulbs is very low, but nevertheless sufficient to be visible to the naked eye in conditions of near or total darkness, and being selfpowered they are not affected by external power failures, nor do they need to be switched on in the event of a power failure.

However, the extremely low light output from such bulbs is disadvantageous in that, in the event of an emergency involving a sudden failure and a consequent sudden plunge into conditions of near or total darkness, the human eye takes some seconds or even minutes to adapt and for the still illuminated sign to become visible. In an emergency, those few seconds can be all important when it comes to a question of survival.

The present invention seeks to overcome this problem by providing such tritium powered luminescent signs with a second luminescent light source which serves to boost the light output from the sign to render the sign more easily visible to the naked eye in an emergency.

In accordance with the invention, this is achieved by mounting the tritium bulb in a housing and providing a phosphorescent reflector positioned in the housing to reflect light from the tritium bulb to the exterior of the housing, usually but not necessarily through a translucent panel positioned in the housing in front of the bulb, that phosphorescent reflector incorporating a phosphor having an pxcitation wavelength in the visible band of the electromagnetic spectrum, or having such a phosphor incorporated into a phosphorescent coating provided on the surface of the reflector.

As will be apparent, the phosphorescent coating on the reflector will supplement the light output from the tritium bulb, although in the absence of excitation energy of appropriate wavelength from an external source, e.g. daylight or other ambient light source, that supplemental phosphorence will gradually diminish leaving only the light emitted by the tritium bulb plus any residual phosphorescence resulting from the continued excitation of the phosphorescent coating on the reflector by the light from the tritium bulb.

In an emergency involving the sudden extinction of ambient lighting, the effect will be that light output from the self illuminated sign will be greater than that from the tritium bulb alone, so that the sign will be more easily visible to the naked eye as it adjusts to conditions of total or near total darkness and so that by the time the phosphorence from the phosphorescent coating decays the eye will have adjusted.

As will be apparent, there are a whole range of different phosphors of different colours and different decay rates, ranging from a few seconds to several minutes or more, that can be used to provide the phosphorescent coating on the reflector. The selection of the appropriate phosphor and techniques for coating that phosphor onto the reflector are well within the ability of the person of ordinary technical skill in the art of phosphorescent coating techniques.

Alternatively the phosphor may be incorporated in a known manner as a pigment into a polymeric matrix and moulded to provide a phosphorescent moulded plastic reflector.

The principle of the invention is illustrated by the accompanying diagrammatic drawing.

In the drawing, 1 represents a housing of a self-powered luminescent sign with a translucent front panel 2. In the housing is mounted a reflector, e.g. an elongate parabolic reflector 3, having a phosphorescent coating 4 on its reflective surface and comprising a phosphor having an excitation wavelength such that it is energised by ambient light e.g. daylight or incandescent light transmitted through the front panel 2. Alternatively the reflector is a moulded phosphorescent plastics structure having a phosphorescent pigment incorporated into the polymer.

Suitably mounted at the focus of the reflector 3 is a tubular tritium powered light bulb 5 of known type comprising tritium gas sealed in a glass envelope coated on its inside surface with a phosphorescent coating comprising a phosphor which is excited by the radioactive tritium The sign thus has a dual light source, one long term, i.e. the tritium bulb 5, and the other short term, the phosphorescent reflector 3.

Claims

1. A self-powered luminescent sign comprising a housing, a tritiumcontaining bulb mounted in the housing and phosphorescent reflector positioned in the housing to reflect light from the tritium bulb to the exterior, said phosphorescent reflector incorporating a phosphor having an excitation wavelength in the visible band of the electromagnetic spectrum, or having such a phosphor incorporated into a phosphorescent coating on the surface of the reflector.

2. A luminescent sign according to claim 1, wherein the reflector is an elongate parabolic reflector with an elongate tubular tritium bulb positioned along the axis.

3. A luminescent sign according to claim 1 or 2, wherein the housing provides a translucent front panel positioned in front of the bulb.