IL46810A

IL46810A - Electric gas discharge lamp

Info

Publication number: IL46810A
Application number: IL46810A
Authority: IL
Original assignee: Philips Nv
Priority date: 1974-03-15
Filing date: 1975-03-12
Publication date: 1977-01-31
Also published as: YU59775A; NL7403467A; FI57853C; AT339428B; ATA189875A; DK101175A; DE2509931C3; CA1020620A; BE826651A; BR7501449A; NL165605C; JPS53867B2; JPS50127480A; FI750713A7; DE2509931B2; AR209763A1; NO140156B; AU7914875A; SE7502740L; NO750833L

Description

Eleetrl gas discharge gas discharge The invention relates to an electric gas discharge lamp in which radiant energy emitted by the gas discharge is converted by means of luminescent material disposed on a missive support into radiation in the visible part of the The invention relates in particular to gas discharge lamps in which the discharge is produced in a mercury vapour which lamps may be or mercury vapour In the former type of lamps the luminescent material generally is disposed on the interior surface of the wall of the discharge space in the second type of lamps the luminescent material usually is disposed on a bulb which encloses the discharge tube In order obtain a given desired colour rendition of such lamps with a high light output it has already been proposed to blend different luminescent materials with one another or to apply them to the support in superposed According to patent specification the procedure starts from a desired chromaticity point which can be achieved with a given light output and a given colour rendition by means of a single layer which comprises a blend of luminescent As as this purpose can be accomplished by means of a blend of more expensive and less expensive luminescent according to the patent a saving is obtainable by using superposed the material of the layer which is directly disposed on the support being cheaper than the material in the layer or layers the for it has been found that thus a lesser amount of the more expensive material is required than when all the materials are blended in a single The distinct layers together produce light having the desired chromaticity but the chromaticity points of the light from the separate layers naturally are This is a great because it was found in practice that in the manufacture of the lamps the thickness of the in particular the thickness of the layer facing the must be kept within very narrow as the chromaticity points of the radiations from the different layers are dif even a small variation in the thickness of this which for considerations of cost must be made as thin as possible but still is to convert the larger part of the radiation of the discharge into produces a considerable change of the chromaticity point and of the colour rendition of the In mass production such requirements obviously are because they lead to expensive inter alia since all stages of manufacture of the lamps have to be thoroughly If the desired combination of very good colour rendition and high light output is obtainable only by employing expensive luminescent the use of the principle of the patent specification 3 gives substantially no for all such materials are expensive and the small saving which may be obtained by applying the least expensive material in a separate layer more remote from the discharge is at least partly nullified by the additional cost of applying such an additional In many cases it will even be cheaper to blend all the luminescent materials together and to apply them in a single An electric gas discharge lamp according to the invention has a luminescent screen which comprises a transmissive support on which are disposed two superposed luminescent layers which each on excitation by the radiation emanating from the discharge emit the layer nearer the discharge consisting of a luminescent material which per unit weight is more expensive than the material of the other luminescent and is characterized in that the difference between the points of the light emitted by either of the layers is less than 3 5 where represents that part of the overall amount of radiation emanating from the discharge and converted into light which is converted by the luminescent layer which faces the and lies between the values and The aforementioned CIE units were published in Paris in in a report of the Congress held in Vienna in 1 The aforementioned case that all the luminescent materials required for satisfactory colour rendition and high light output are expensive for in lamps in which the layer facing the discharge comprises a blend of three luminescent materials activated by rare earth metals and having line emissions between and between and nanometers and between and 630 When using the characterizing principle of the invention the amounts of all these expensive luminescent materials can be greatly reduced without losses in light and whilst retaining the satisfactory colour as will be shown hereinafter with reference to A condition as w s stated that at least 80 and at most of the total amount of radiation converted into light is converted by the layer which faces the If this layer contributes less than 80 a small deviation from this value has a paratively great influence on the colour rendition of the light emitted by the if the layer contributes more than 99 amount of saving is too Preferably the contribution is selected to exceed The invention will now be described more fully with reference to Examples and to a drawing which schematically shows a mercur vapour lamp according to the Referring now to the reference numeral 1 denotes the wall of the discharge The discharge space accommodates electrodes 2 and The discharge is produced by means of these electrodes in discharge space which is filled with mercury vapour and one or more noble as is usual for lamps of such The inner surface of the lamp wall 1 is coated with two superposed luminescent layers 4 and is with suitably selected voltages a discharge is produced in the discharge space of the which discharge emits largely ultraviolet in particular at a wavelength of This radiation excites the luminescent materials in the layers and Depending upon the natures of these materials the layers each emit radiation having a specific spectral energy distribution and a given chromaticity the radiation emitted the lamp being the sum of the radiations of each of the layers 4 and According to the principle of the invention the layer comprises a luminescent material or a blend of luminescent materials which per unit weight is less expensive than the material or the blend of materials in the layer chromaticity points of the radiation of the two layers are as mentioned be the difference does not exceed 5 In the layer at least and at most of the ultraviolet radiation is converted into The part of the ultraviolet radiation which is not converted in this layer is converted in the layer substantially entirely into light having chromaticity point equal to or slightly different from the chromaticity point of the light emitted by the layer Superposition of the layers and permits of making the layer thinner than if the layer were absent whilst retaining substantially the same light This will be seen from Table I which shows figures measured on a watt fluorescent TABLE I In Table A is a luminescent material of the formula Ba 0 B is a luminescent material of the formula Ce 0 i 9 C is a luminescent material of the formula Y In the Table numbers 1 and denote reference lamps not constructed according to the invent A comparison of the lamps 2 3 and with the reference lamp 1 shows that after 100 hours there is substantially no difference in light chromaticity coordinates and colour the lamps 2 and contain a considerably smaller amount of the expensive materials B and A comparison of the lamps 6 and 7 with the reference lamp 5 gives a similar Only the Ra value has decreased considerably in the lamp 7 only 1 1 g of the blend of the materials B and C is with a resulting large saving in Accordingly the value of the conversion factor is low in this very thin namely In the lamp the value of is about 87 An impression of the variation of the light output as a function of the layer thickness in a lamp which contains only one layer of a blend of o of B and of C is given by the following Table TABLE II TABLE II Layer weight relative light output 100 A comparison between the values of Table II and those of Table I shows clearly that the losses in light which would be produced by reducing the thickness of the layer in a layer which naturally would also give a cheaper do not or occur in a considerably lesser in the lamps according to the invention Applying the various layers in the lamps according to the invention may take place in an entirely conventional for example by mixing the luminescent materials concerned with a such as ethylcellulose or in a of butyl acetate or another coating the tube wall with such a drying and heating to remove the Although in the above a low pressure mercury vapour discharge lamp was given as an the principle of the invention is without essential modifications to other for example to high pressure mercury vapour discharge insufficientOCRQuality

Claims

PHN .7 7- 23. 1 . 1 75

1. Electric gas discharge lamp having a luminescent screen which comprises a light -transmis sive support on which two superposed luminescent layers are disposed which each on excitation by the radiation emanating from the discharge emit light, the layer which faces the discharge consisting of a luminescent material which per unit weight is more expensive than the material of the other luminescent layer, characterized in that the difference between the chromatic ity points of the light emitted by either of the layers is less than * ^ CIE units, where 1-P p_ represents that part of the total amount of radiation emanating from the discharge and converted into light which is converted by the luminescent layer which faces the discharge, and p_ lies between the values 0 .80 and Ο. 99 .

2. . Electric gas discharge lamp as claimed in Claim 1 , characterized in that the luminescent layer more remote from the discharge comprises one or more halophosphates of calcium and/or strontium activated by antimony and/or manganese and the layer facing the discharge consists of a blend of three luminescent materials which are activated by rare earth metals and have line emissions between 430 and 90 nanometers, between 5 0 and 565 nanometers and between 590 and 630 nanometers respectively. 3 · Electric gas discharge lamp as PHN.7^7 23.1. '75 claimed in Claim 2, characterized in that the layer which faces the discharge consists of a blend of yttrium o ide activated by trivalent europium, cerium magnesium aluminate activated by trivalent terbium and barium magnesium aluminate activated by divalent europium.