A LIGHT HOUSING PROVIDED WITH AN AFTERGLOWING COATING, THE COATING USED FOR THAT PURPOSE AND THE COATING METHOD USED FOR THAT PURPOSE

Abstract: A light housing, such as a light box or a light source of an at least partially transparent material, characterized in that at least part of said light housing is provided with an illuminating coating. In a preferred embodiment, the coating is a dispersion with a base of cellulose, acrylate, epoxy or polyurethane, or is a foil, for example a shrink foil provided with an afterglowing pigment of an alkaline-earth metal-containing aluminate, which is doped with one or more transition metals.

Description: A LIGHT HOUSING PROVIDED WITH AN AFTERGLOWING COATING, THE COATING USED FOR THAT PURPOSE AND THE COATING METHOD USED FOR THAT PURPOSE The invention relates to a light housing, such as a light box or a light source of an at least partially transparent material . The term light source as used herein is understood to mean an incandescent lamp or a tube lamp, for example, and the term light box is generally understood to mean a light casing, a lamp shade or other devices which enclose a light source at least partially. A normally operating, energized light source generally emits "white" light. When the current supply to the light source is interrupted, for example in case of a power failure caused by calamities, such as the blowing of a fuse, fire and the like, or when part of the light source just breaks down, for example when a filament burns through, or when the light source is turned off, the room darkens. When such darkening is undesirable, numerous problems may arise. Generally, persons who were carrying out activities in such a room cannot resume their activities until the light source emits light again, for example. In particular in case of an emergency, such darkening generally leads to panic reactions and the persons have difficulty in getting their bearings in the dark, in particular when they have to leave said rooms. Usually it will be necessary in such situations to revert to the use of light sources which operate independently of a power source, for example pocket lights and candles. It is an object of the present invention to obviate the above drawbacks. To that end, the invention provides a light housing which is at least partially provided with an illuminating coating. When the current supply to a light housing according to the present invention is interrupted, visible light will still be emitted, due to the action of the illuminating pigments, at positions where such a light action is expected, namely by the light source itself or by a light box enclosing said light source. Thus, it is not necessary for the persons who are present in such a room to remedy the calamity at once, since the light that is still being emitted is sufficient to enable them to complete the normal activities. In case of a dangerous situation, such as a fire, people can leave the room without any problem, since a sufficient amount of light is still available. Possible panic reactions are suppressed in this manner. The invention thus provides a safe and secure solution for the problems which may arise in case of undesirable darkening. The term afterglowing pigment as used herein is understood to mean a fluorescent and/or phosphorescent pigment . Fluorescence is the process whereby radiation is emitted as a result of a transition between molecular energy levels exhibiting the same spin condition, whilst in the case of phosphorescence, radiation is emitted as a result of a transition between two molecular energy levels exhibiting different spin conditions. Fluorescence is of very short duration, and generally it only occurs visibly when a fluorescent pigment is exposed to light. Phosphorescent pigments, however, are capable of emitting light for a much longer period of time after being exposed to light, however. Another advantage of fluorescent as well as of phosphorescent pigments is the fact that they are both capable of emitting light of a different wavelength or a different wavelength range than the light to which they are exposed, or to which they were initially exposed. Such a pigment is thus capable of emitting light of a particular colour or tint upon or after exposure to for example "white light" . Illuminating pigments are activated by natural light or by other light sources. In the dark, for example in case of a power failure, the absorbed light is immediately emitted. This makes it possible within the framework of passive safety to use said photo-illuminating light housings as signal generators in case of the above calamities, such as a power failure. An additional advantage of such light housings is the fact that the light from the light source is directly absorbed by the photo-illuminating pigment. When the natural light becomes dimmer or when the light sources are extinguished, actively or not actively, the pigment will start to emit the absorbed light. A light housing according to the invention is in particular provided with a coating consisting of a dispersion with a base of cellulose, acrylate, epoxy or polyurethane, or of a foil, for example a shrink foil provided with an afterglowing pigment of a alkaline- earth metal-containing aluminate, which is doped with one or more transition metals. Such a coating can be applied thinly, since said illuminating pigments have a small grain size of approximately 7 - 10 μm. The afterglowing or illuminating pigment can be exposed to light having a wavelength range of about 350 - 450 n, preferably of about 380 - 400 nm. The afterglowing pigment preferably emits light wherein the wavelength maximum lies at about 520 nm and the wavelength range of the emitted light is about 475 - 575 nm. The persistence and the intensity of the afterglow in accordance with Din 67510, Part 4 (1995) of the afterglowing pigment is at least 1,350 minutes, preferably at least 2,000 minutes with a visibility limit of 0.3 mcd/m 2 . The intensity of the light being emitted by the afterglowing pigment after 5 minutes is at least 170 mcd/m 2 , preferably at least 400 mcd/m 2 , after 30 minutes it is at least 25 mcd/m 2 , preferably at least 65 mcd/m 2 , and after 20 minutes it is at least 5 mcd/m 2 , preferably at least 11 mcd/m 2 . The the light housing according to the invention is preferably provided with a coating wherein the charging degree of the afterglowing pigment is 10 - 80%, preferably 20 - 50%. This provides a perceivable light intensity for a duration of at least 8 hours, which makes it possible to find the exits when darkness sets in or when the lights go out due to a calamity. A light housing according to the invention preferably comprises a coating having a layer thickness of 10 - 100 μm, for example 50 μm. The coating according to the invention is particularly suitable for being used as an outer layer on a prefabricated light housing. The provides the additional advantage of protection against breakage, for example in the case of glass fracture of a light source, whereby fragments of glass that may have come loose are confined. Such a thin layer will not visibly interfere with the light emitted by the light source, so that the transparency remains ensured. In case of an interruption in the power supply, the initial light output of the light housing according to the invention will preferably be at least higher than 3,000 mcd/m 2 , more preferably at least 5,000 mcd/m 2 . One preferred embodiment is a light housing according to the invention in the form of a fluorescent tube. Since such a fluorescent tube has a large surface area, a substantial afterglow action can be obtained due to the action of the large surface area of the coating. For the same reasons, the generally known energy-saving lamps constitute a preferred embodiment of a light housing according to the invention. The invention furthermore relates to an illuminating coating with a base of a dispersion, for example a cellulose, acrylate, epoxy or polyurethane dispersion or a foil provided with an afterglowing pigment of an alkaline-earth metal-containing aluminate, which is doped with one or more transition metals, and to a method of applying such a coating to a light housing. The coatings, for example with a base of a polyurethane dispersion or another plastic emulsion or dispersion, are directly applied to the glass of the light housing, the light source or the light box by dipping or by using another application technique. Said coated light sources can be fitted in the usual light boxes or lamp holders. A coating with a base of a foil of LDPE or PE, for example, preferably a shrink foil, for example of modified vinyl acetate, can be applied to the light housing directly after the manufacture thereof as a subsequent finishing step. The advantage of using a shrink foil is that a tightly fitting, dust-proof and moisture-proof illuminating coating is obtained. The light housings may first be subjected to a pre- treatment step, for example an etching step or another, 6 mechanical operation, such as blasting or sanding. The application of a primer may render such a pre-treatment step superfluous. A uniform coating is applied to the glass in a layer thickness of approx. 10 - 100 μm by dipping, after which drying and curing follows. A layer thickness of 20 - 70 μm is preferred. Such a thin coating disturbs the normal light action only minimally. Said dipping may take place in two directions, so as to obtain a homogeneous coating. According to to technique, the light source, such as a tube, a lamp etc. is rotated horizontally in the coating, thus obtaining a uniform coating in one operation. This coating can only be applied by means of a paint brush or by using a spraying technique. Possibly, the coating may be provided with a colourless finishing layer.

Claims: CLAIMS 1. A light housing, such as a light box or a light source of an at least partially transparent material, characterized in that at least part of said light housing is provided with an illuminating coating. 2. A light housing according to claim 1, characterized in that said coating is a dispersion with a base of cellulose, acrylate, epoxy or polyurethane, or is a foil, for example a shrink foil provided with an afterglowing pigment of a alkaline-earth metal- containing aluminate, which is doped with one or more transition metals. 3. A light housing according to claim 1 or 2, characterized in that said coating comprises an afterglowing pigment exhibiting a charging degree of 10 - 80% 4. A light housing according to claim 3, characterized in that said coating comprises an afterglowing pigment exhibiting a charging degree of 20 - 50%. 5. A light housing according to any one of the preceding claims 1 - 4, characterized in that said coating has a layer thickness of 10 - 100 μm. 6. A light housing according to claim 1, characterized in that said illuminating coating is provided on the light housing as an outer layer. 7. A light housing according to any one of the preceding claims 1 - 6, characterized in that the initial light output following an interruption of the power supply is at least higher than 3000 8 mcd/m 2 . 8. A light housing according to any one of the preceding claims 1 - 7, characterized in that said light housing is a fluorescent tube. 9. An illuminating coating obviously suitable for coating a light housing according to any one of the preceding claims, with a base of cellulose, acrylate, epoxy or polyurethane, or a foil, for example a shrink foil provided with an afterglowing pigment of a alkaline-earth metal-containing aluminate, which is doped with one or more transition metals. 10. An illuminating coating according to claim 9, characterized in that said foil is a shrink foil. 11. A coating according to claims 8 - 10, characterized in that said pigment exhibits a charging degree of 20 - 50%. 12. A method of coating a light housing with a coating according to claims 9 - 11, characterized in that said light housing is pre-treated by means of a chemical agent, such as HF, or by means of a mechanical operation, such as blasting, sanding, etc., or provided with a primer, wherein a coating is applied to the light housing in a layer thickness of 10 - 100 μm. 13. A method according to claim 12, characterized in that a colourless finishing layer is applied to said coating.

Inventors: BEELE JOHANNES ALFRED, BEELE, JOHANNES, ALFRED
Applicants: BEELE ENG BV, BEELE JOHANNES ALFRED, BEELE ENGINEERING B.V., BEELE, JOHANNES, ALFRED
Application year: 1999
Main classification: F21V9
IPC codes: C09K11, F21V9