PHOSPHORESCENT DEVICE

Abstract: This invention relates to a phosphorescent device for use in for instance a light box for a meeting hall for indica­ tion of an exit out of the same. According to the invention the device comprises a trans­ lucent fabric (6) of a special material which at least on its one side is coated with a layer (7) of luminous colour having the ability to absorbe and store light so that, if the light surrounding the device should die out, the device continues to light during a relatively long time after that.

Description: This invention relates to a phosphorescent device for use in for instance a light box for a meeting hall for indication of an exit from the same. Such light boxes are common at the exit doors of emergency evacuation in meeting halls and similar spaces and the purpose of these boxes is that they shall continue to light in fire and similar emergency situations when the main current disappears so that the emergency exits become clearly indicated for those people who shall evacuate the hall. The light boxes usually have a parallelepipedic form and are placed above each emergency exit. Inside the box there is a light source usually a fluorescent tube which is lit when the main current is on, whereby the word "OUT" on the front portion of the light box, which front portion as a rule comprises a plastic plate, lights out of the hall. According to the law the light box has to be provided with some form of light in reserve so that the box continues to light even if the main current should disappear. This light in reserve is made possible by chargeable dry batteries which are placed inside the light box. Batteries are perishables which are very quickly destroyed in the warm environment that quite naturally arises inside the light box where the fluorescent tube always lights. In order to be quite sure of the function of these dry batteries they have to be controlled at least every third month and be exchanged when that is necessary. These control and exchange measures become very expensive and therefore they are not taken to the necessary extent. Due to that fact the risk is very great that the batteries and accordingly the current in reserve does not function in a real emergency situation. Investigations have appeared that only about 20% of the light boxes would function in a real emergency situation. Of course this is a clear deficiency from a safety point of view. By the American patents 4 420 898 and 4 466 208 devices are previously known which comprise a phosphorescent material. In this case, however, the phosphorescent material is embedded in a vinyl plate (4 420 898) and in a transparent plate (4 466 208), respectively. That means that the rays of light coming in towards and hitting the known plates with the phosphorescent material are not subjected to any reflecting influence but essentially move past the crystals of the phosphorescent material without activating these other than marginally. The result becomes a bad phosphorescent action during a very short time. Other known devices are shown in FR-A-831 805, GB-A-672 762 and US-A-2-436 182. The first document, FR-A-831 805, discloses a device, which in contrast to the device according to this invention uses the fluorescence technique. Moreover, the device comprises a plate instead of a fabric. Also the second document, GB-A-672 762, refers to the fluorescence technique and accordingly discloses a device which cannot be compaired with the device according to this invention. The third patent discloses a phosphorescent device consisting of a composition of a translucent material and a phosphorescent material. Thus, the phosphorescent material is mixed with the translucent material. That means that this known device is very complicated and, therefore, becomes expensive to manufacture. Moreover, the result will not be very good. The present invention intends to solve the problems with the known technique and offer a reliable phosphorescent device which can be used in light boxes and in other arrangements and which has the ability to be able to maintain the intensity of light so that the guidance of the device is maintained during a long time after the darkening of the lamp of the light box. This has been achieved by a device of the kind mentioned by way of introduction which is characterized by the features mentioned in the following claims. By being designed in this way the device can suck up light from all directions and store it. That means that in the case of the light box the device is charged irrespective of if the light comes from the outside or from the inside. Two embodiments of the invention will be described more closely with reference to the accompanying drawing where Fig. 1 shows a light box known on the market and placed above a door leading out from a room; Fig. 2 shows a horizontal cross section of the light box according to Fig. 1; Fig. 3 shows a horizontal cross section of a front plate according to a first embodiment of the invention which front plate can be used in a known light box of that type shown in Figs. 1 and 2 or in other types of light boxes and Fig. 4 shows a horizontal cross section of the front portion of a light box according to a second embodiment of the invention. In Figs. 1 and 2 there is shown a known light box 1 which as has been mentioned previously, is intended to be placed above a door 2 in a meeting hall 3 which door is intended to be an emergency exit. This light box comprises a fluorescent tube 4 always lighting, that is also on occasions when the light in the hall dies out. The light from the fluorescent tube 4 is intended to come out into the hall by the front portion 5 of the light box which as a rule comprises a plastic plate so designed that it is possible to read on the same the word "OUT", "EXIT" or the like. The light box also encloses at least a lamp in reserve driven by dry batteries and which shall begin to light if the main current is cut off with the consequence that the fluorescent tube dies out. As has been mentioned previously it does not function in that way in reality. The solution of the problem is a phosporescent device according to the present invention. A first embodiment of the invention is illustrated more closely in Fig. 3 showing a cross section of a front plate of a light box. The front plate comprises a translucent fabric 6 of glass fibre which is coated with a layer 7 of luminous colour. The layer of luminous colour comprises crystals of zinc sulphide having the ability to suck up and store incoming light, whereby the layer of luminous colour becomes phosphorescent. Due to the fact that the fabric 6 of glass fibre allows the light to pass through, the layer of luminous colour can be charged by light from all sides. The fabric of glass fibre has wave form in cross section. Due to the fact that the luminous colour is in the form of a separate layer on the outside of the fabric it is possible for the crystals of zinc sulphide to be collected in the wave troughs of the fabric of glass fibre which partly means that the number of crystals per unit of the area becomes great, partly means that the crystals of zinc sulphide get the ability to reflect the incoming rays of light between themselves. This leads to a better storage of the light from the rays of light in the crystals of zinc sulphide leading to that these ones become charged through. This in its turn leads to a prolonged lighting time. Another essential contribution to the prolonged lighting time is the fact that the fibres of the fabric of glass fibre have the ability to spread the incoming rays of light so that as many crystals of zinc sulphide as possible are hit by the rays of light. The new front plate is very suitable to be used as a front plate 5 in light boxes existing on the market, the layer 7 of luminous colour being intended to be positioned farthest away with the fabric layer 6 inside and accordingly facing the fluorescent tube. On the outside of the layer of luminous colour a plastic tape is intended to be fastened, for instance with the text "OUT". The surface on this layer of luminous colour, however, is rough and therefore it could be hard to fasten the plastic tape properly. The embodiment according to Fig. 4, however, solves this problem. This embodiment like the first one has a layer 6 of glass fibre coated with a layer 7 of luminous colour. On the outside of this layer of luminous colour there is another layer 8 of luminous colour. Farthest away on the device there is a plane plastic plate 9 placed. When manufacturing the front portion the layer 8 of luminous colour is suitably applied against the inside of the plastic plate 9, whereafter the plastic plate with the layer 8 of luminous colour is applied against the first layer 7 of luminous colour. Since the plane plastic plate 9 is positioned farthest away, it constitutes the part of the device that the tape with the text shall be fastened on. Due to that fact there is created a good base for the tape resulting in that it can be fastened properly. According to this embodiment two layers 7 and 8 of luminous colour are placed between the layer 6 of fabric of glass fibre and the plastic plate 9. Of course it is possible to have only one layer. One of the advantages with the invention according to the two described embodiments is that the layer of luminous colour is charged not only by the light outside the light box but also by the light from the fluorescent tube inside the light box which tube is always lit. That means that the layer 7 of luminous colour of the device is charged also during the time when the light outside the light box, that is out in the hall, is switched off. If the main current in a hall should be cut off having the consequence that not only the light in the hall but also, the fluorescent tube in the light box die out, the light box still continues to light because the layer of luminous colour in the front portion of the box has become phosphorescent by the charge and can during a time of several hours after the current cut off indicate where the emergency exit is. Investigations have shown that the intensity of light of the device has diminished so slowly that the device has given guidance during eight hours after a current cut off. A further advantage with the new device is that it does not require maintenance at all because it has no unit in reserve with dry batteries which should need to be controlled and be exchanged if required. According to the described embodiment it has been stated that the fabric is made of glass fibre. Of course it is within the scope of the invention to use a fabric of another material. Furthermore, it has been suggested that the layer of luminous colour comprises crystals of zinc sulphide. In this connection the number of crystals per square centimetre ought to be about 12 000. Of course the layer of luminous colour can be of another kind. Furthermore, light boxes for emergency exits are only one of several possible areas of use for the invention.

Claims: A phosphorescent device for use in for instance a light box for a meeting hall for indication of an exit out of the same, characterized by the combination of the following features: The device has a first layer comprising a translucent fabric (6) having the ability to spread incoming rays of light; The device has a second layer (7) comprising a luminous colour provided with crystals, the colour coating one side of the fabric and having the ability to absorbe and store light; The fabric has wave form in cross-section so that it is provided with wave troughs, whereby the crystals of the luminous colour are collected in the wave troughs of the fabric for a good storage of incoming rays of light. A device according to claim 1, constituting a front portion in a light box enclosing a fluorescent tube, characterized in that the layer (7) of the luminous colour of the device is positioned on the outside, having the consequence that the layer (6) of the fabric faces the fluorescent tube (4). A device according to claim 1, constituting a front portion in a light box enclosing av fluorescent tube, characterized in that the front portion besides the layer (6) of the fabric and the layer (7) of the luminous colour also comprises a plane plastic plate (9) positioned on the outside, whereas the layer (6) of the fabric is positioned on the inside and accordingly faces the fluorescent tube (4). A device according to claim 3, characterized in that the front portion comprises a further layer (8) of luminous colour which is applied at the inside of the plastic plate (9) and which when manufacturing the front portion is accordingly applied against the first layer (7) of the luminous colour. A device according to any one of the preceding claims, characterized in that the fabric (6) is made of glass fibre. A device according to any one of the preceding claims, characterized in that the layer (7,8) of the luminous colour comprises crystals of zinc sulphide.

Inventors: SEFASTSSON, LARS
Applicants: SEFASTSSON, LARS
Application year: 1988
Main classification: G09F13
IPC codes: G09F13, F21S8, F21S4