US1943877A - Lighting unit - Google Patents

Description

Jan. 1e, 19345A n. A. s. PAGET 1,943,877'v y I LIGHTING UNIT original Fi1ed'Jan.,4,'1929 4 Smets-sheet' 1 R. A. S.- PAGET Jan. 16, 1934.

LIGHTING UNIT Original Filed Jan. 4, 1929 4 Sheets-Sheet 2 AJan. 16, 1934. R. A. s. PAGET 1,943,877

LIGHTING- UNIT original Filed Jan. 4, 1929. 4 sheets-sheet 3 Jan. 16, 1934. l R A, s, PAGE-r LIGHTING UNIT 4 sheets-Sheet '4 Original Filed Jan. 4, 1929 Patented jan. i6, 1936i 1,943,877 LIGHTING UNIT Richard Arthur Surtees Paget, Lancaster Gate; England, assignor to Thermal Syndicate Limited, Neptune Bank; Wallsend-on-Tyne, England l Application January 4, 1929, serial No. 330,318. and in Great Britain January 7, 1928. Renewed June 14, 1933 4 Claims. (Cl. 24o- 4.1)

coloured globes or to use the light from a lament lamp only after reflection from coloured surfaces. Colour screening or colour reflecting devices are not desirable, however, owing to the' resultant reduction ofthe lighting efficiency of the filament lamps. It has also been suggested to provide a composite lighting unitconsisting of a quartz mercury arc lamp and filament lampo arranged so that the chemically active ultraviolet rays of the quartz lamp may be combined with the ultra-red radiations from the lament lamps, the reason for the addition of the filament lamps, being to improve the colour` of the radiation from the mercury lamp. No explanation however has been given as to the extent of this addition or of the colour quality desired. Moreover, Where such a lighting unit is used as a general illuminant, it has not been proposed to provide protection from the injurious short 'wave length radiations from the mercury arc, and with the unscreened mercury arc, dangerous sunburnin'g would occur if the unit were used as an 'ordinary source of illumination.

According to the present invention I provide a high efficiency lighting unit, approximating to daylight both as to its visible and ultra violet content, by combining Within a casing,1lamps of different character, Whose radiations are complementary in relation to wave length for exs ample mercury vapour lamps or other lamps producing ultra violet rays and metal filament lamps, ,the combined radiations being transmitted by a layer of translucent fused quartz or the equivalent, so proportioned as to-thickness and texture as to transmit only the radiations required. The quantity of illumination to be used from each source is determined so that the resulting visible radiation is brought as close as possible to' the quality which exists in ordinary daylight. I further specify the materials and methods which are required to produce this illumination together with a safe land tolerable amount of ultraviolet radiation.`

Because of the Way in which the mercury lamp emits its radiation, that is to say, discontinuously, so far as` the spectrum is concerned, a complete match With ordinary daylight is not possible by the addition of filament lamps but thel composite radiation which I produce by the method hereinafter described is not further removed from daylight values on the blue side .than is the v filament illumination removed on the red side.

The features which I have found require experimental investigation in making a lighting unit to fulfill the required conditions are:

1st. The ratio of filament and mercury arc illumination. 2nd. Theensuring of a uniformly illuminated bowl surface. 3rd. Proper ventilation, and 4th. Control of the amount of ultra violet radiation sent out by the lamp.

Taking these features in turn, it is desirable to use the maximum amount of mercury arc illumination permissible in order to increase the lighting efficiency of the unit as much as possible, since, as is Well known, the mercury arc lamp has a higher luminous efficiency than ordinary filament "w lumens per watt with the radiation from one direct current mercury vapour arc contained in a quartz tube 6 inches long and 15 millimetres external diameter consuming 400 watts together with its series resistance and operating at an overall eiiiciency of about 15 lumens per watt, a very 4fair approximation to the quality of ordinary daylight is obtained. In this case an equal Wattage is supplied to both systems. These figures are given only by way of example and I do not limit myself to these specific amounts of filament and mercury arc illumination. Smaller or larger units may be prepared retaining about the same ratio of filament to mercury arc illumination. The proportion of illumination from'themercury arc may be increased so that a greater proportion up to a maximum of twice the amount indicated of mercury arc illumination is used, still producing a lamp which functions under the required conditions, although the precise ratio specified gives the best match to daylight. I have given the power consumption of the mercury vapour lamp with reference to a direct current burner running at a specified efficiency but no restriction is to be placed on the type of burner whether alternating or direct current, provided that it operates substantially in the range Where itsl efficiency is between 15 to 30 lumens per watt. With more efficient mercury vapour lamps the power consumption required for this part of the unit-is to be reduced pro rata for its increase in eiciency above 15 lumens per watt so that the desired ratio of filament and mercury arc illumination is kept in the proportions already set out. Similarly for filament lamps of greater or less efficiency than 11 lumens per watt. y

In order to limit the amount of ultra-violet radiation the assembled lamps are enclosed by a screening and diffusing bowl of translucent fused silica or quartz or other suitablematerial which will transmit the ultra violet rays of the desired wave length and to produce uniform illumination on the surface of the enclosing bowl I find it l best to arrange the various units symmetrically with reference to the axis of the bowl.

To maintain `this uniform illumination with `lamps of diilerent brilliancy and colour values careful spacing of the various lamps away from the surface of the screening bowl is required. At the same time to safeguard the user, provision must be made that no radiation from the mercury lamps reaches the working plane unless after passing through. the obscuring bowl or after reflection.

In the accompanying drawings I have shewn examples of preferred constructions of lamp units in accordance with the invention. Figure 1 shews an elevation in part section lof aunit designed for use with the resistance of the mercury lamp unit similar' to that shewn in Figure l, but arranged to accommodate the ballasting resistance for the mercury vapour lampl in the upper part of the housing; Figure 4 is similar to Figure l, but adapted for use with a mercury vapour lamp of the atmospheric type where no tilting arrangement is required to start the arc; Figures 5 and 6 give a general View in elevation of a unit similar to that shewn in Figure 1 and illustrating in Figure 6 how the lower bowl may be opened on its hinge for cleaning purposes; Figures '7 and 8 shew a similar unit to that shewn in Figures 5 and 6; Figures 9 and 10 shew in elevation and plan a lighting unit in which a mercury vapour lamp surrounds a filament lamp.

Referring to Figures 1 and 2 the construction shews a straight arc tube lamp l, around which are symmetrically arranged .four lament lamps 2, in the diametral plane of the approximately hemispherical silica bowl 3, which serves to enclose the lamps. Additionally, reflectors 4, may be added disposed at an angle to the axis of the arc tube to distribute the radiation from the mer-- cury arc into those portions of the bowl 3, not well illuminated by it, particularly those portions lying near to the electrode chambers 5 and 6 of the arco Similar reflectors may be used suitably arranged to throw the rays from the filament lamps on to that part of the bowl which would otherwise be in shadow such shadow being caused by another detail of the assembly.

Double metal rings 7 and 8 carry the upper silica bowl 9 and the lower silica bowl 3, the inner ring 7 being hinged to the outer ring 8 to give easy access to the lower bowl for cleaning purposes, as shewn in Figures 5 and 6.

The arc tube shewn is of the vacuum type and is provided with the usual tilting mechanism.

-When the unit is in operation air currents pass in through holesv 11, drilled in the double rings 7 and 8, and out at the top 'through the aluminium cover 12.

.the mercury vapour lamp 1.

In Figure 3 supports'l`3 carry the metal hood 14 and also the platform 15, to which is'xed the tilting arrangement 16 to start the mercury vapour lamp 1. A cylinder '17 of insulating material is provided and on this is wound the ballasting resistance wire which is connected in series with The resistance wire when heated induces a circulation of cooling air within thecasing. The unit is otherwise similarto that shewn in Figures 1 and 2. In operation air vcurrents pass in through holes l1 and through the annular space between the platform 15 and the hood 14, and out at the top as shewn by the arrows.

Figure 4, as hereinbefore mentioned, shews a similar unit to that of Figure 1, except that a mercury vapour lamp 1a, of the atmospheric type is provided.

Figures 7 and 8 shew a similar unit to that shewn in Figures 5 and 6 but in this case the lower Vbowl 3, and its supporting ring 18, is suspended from the main structure by means of three or more chains or cords 19, which pass over pulleys 20. Balance weights 21, are attached to the other ends of these chains orcords. Figure 7 shews the lower bowl in the closed position and Figure 8 shews this bowl lowered for cleaning.

A handle 22, may be attached to the bottom of the bowl 3, as a convenient means for raising or lowering the bowl.

Figures 9 and 10 shew in elevation and plan, a lighting unit having a mercury vapour lamp with its lighting tube 23 arranged in the form of a circle or ring inside which -is placed the filament lamp 24.

In this unit the arrangement with regard to the opening of the light transmitting surfaces or bowls 9 and 3, may be similar to those shewn in the preceding Figures 5, 6, 7 or 8 and can be arranged to suit any particular requirements. In all cases the inside of the bowls should be easily accessible for cleaning purposes: this is important in view of the fact that a small amount of dust accumulation will cut off the ultra-violet radiation.

With the types of enclosing housings which are commonly available when used only with filament lamps the problem of ventilation is not serious and the cooling of these units is principally ac' complished by thermal radiation and convection from the outer fittings and not by an internal circulation of air. I have found that composite units of the type referred to in this specification require careful arrangement so that no interference occurs with the operation of the mercury arc lamp andv also so that injury may not be done to the filament lamps at or about those p ortions where joints are made with metal caps and the like, and indeed also injury directly to the glasses used in this type of lamp, by overheating. To escape such injuryto the filament lamp or lamps and further to maintain the mercury lamp in stable operation at its desired rating I arrange the various components of the unit symmetrically as already specified and assist the natural ventilation of the lamps so that cold incoming air may be directed on to the mercury lamp and-also on to those points of the filament lamp or lamps which require special cooling.

Because of the use of quartz mercury arc lamps in the assembly of the lighting units it is necessary to use a suitable enclosing bowl or fit ting which shall cut down the intensity of ultraviolet radiation in the working plane to a safe limit, and properly diuse and intermingle the light from the various sources which it encloses.

I have found however as the result of experivments that the most suitable material for this purpose is translucent fused silica or quartz, of the general type obtained by fusing pure quartz sand 4and in a thickness between lg and 1/8 of an inch.

lamp so that at common working distances onlyv, a'mild sun-burning effect is obtained upon pro- 20:

tracted exposure. It is generally considered that radiations of a wave Ilength less than 2500 A'. U.

have injurious effects on human tissues and the exclusion of these radiations which are emitted by the mercury vapour lamp is an important advantage depending upon the use of the translucent silica bowl. It is possible further by altering the texture (that is to say, the size and number of air' bubbles in the silica) and increasing or diminishing the thickness of section of bowl used to control the output of ultra-violet radiation from the lamp over a considerable range without interfering much with the transmission of visible radiation. As an example of the control of the bowl upon the output of ultra-violet radiation, with a unit composed of four 100 watt lament lamps 'together with one mercury lampconsuming over all 400 watts in a silica bowl of the type indicated and about T16" thick, exposure at two feet from the assembled unit for two hours produces a sun-burn effect equivalent to that got by exposure to the naked lamp at the same distance for about vthree minutes. Sunburn of this type would be produced by the normal medical dosage of about three minutes and is commonly known as the rst stage of erythema. At greater distances from a unit of the type indicated the intensity of ultra violet radiation falls off much in the same manner as the ordinary visible i1- lumination so that at ordinary working distances say 6 feet, the time of exposure. required for'sunburning is of the order 30 hours or more. Such exposure is quite safe for continuous daily use of the unit as an ordinary source of illumination, and because of the presence of ultra-violet radiation important benefits to the health and well being of the user are to be expected.

I have found, as a result of photo-electrical measurements that by altering the texture of the silica bowl, by partly re-fusing or glazing itin an electric arc, the transmission .of ultra-violet radiation is very much increased without interferingsensibly with its transmission of ordinary visible illumination. The extent of this increase may be as much as eight times when the bowl is glazed from each of 4its surfaces. Thus, by adjusting the extent of this glazing treatment, and/or altering the thickness of the bowl, the transmission of ultra-violet radiation can be accurately controlled, as also the mechanical strength. L

It will thus be seen that when I use a fused silica or quartz bowl I canl control the trans- When the minimum amount of ultra violet rays is required I would use a thick unglazed bowl whilst for the maximum amount of ultra violet rays a thin bowl glazed on both sides would be used and for intermediate strength I have the alternatives such as a thin unglazed bowl or a slightly thicker bowl glazed on one side only. When mechanical strength is of some consideration I prefer to use a fairly thick bowl glazed or not as circumstances require.

I have found, further, as a result of tests that no injurious effects are produced upon the human eye by irregular reflection of ultra-violet radiation from common working surfaces when lamps of this type are used'as a general source ofvillumination. y

Where it is required completely to enclose the lamp which is advantageous to prevent deposition of dust on the transmitting surfaces the up-` per cover of the bowl may be partly of translucent fused silica and partly of metal but the use of fused silica is not essential for I have found, that very little ultra-violet radiation is reflected bythe materials ordinarily used toproduce a white ceiling in a room. In cases when the lamps are intended to be used in a dusty atmosphere as for instance in a factory or warehouse, it would be advisable to make arrangements to prevent as far as possible any dust entering and settling on the inside of the bowls. This can be done by covering all Ventilating holes and the chimney with fine wire gauze. This gauze will also prevent house flies and other .winged insects from entering the lamp and collecting in the bottom of the bowl.

In my description I have exemplified only the use of direct current mercury lamps which have the important advantage of easy starting, but I do not wish to confine myself to this type of bm'ner and nothing in my description is altered in sense if, for mercury vapour lamp either direct or alternating current mercury vapour lamp is read. The lamp may be most simply arranged for distant control by incorporating a'suitable relay with a solenoid, and plunger in mechanical connection with the mercury lamp, so that upon closing the circuit to the lamp, the lamp is tilted continuously until the arc strikes and then this mechanism is rendered inoperative by' the relay.

Aall in the mercury lamp and its resistance, and

400 watts in the filament lamps, the efficiency of the unit in lumens per watts is 4.6, whereas the efficiency of filament lamps only, arranged in a similar partly enclosed diffusing bowl' is only 3.9

lumens per watt, a gain of 8 per cent. It is further preferable in these units to use a mercury lamp of as large a size as is permissible since these are' more efficient, thus by way of example withA a mercury lamp consuming over all 417 watts 65 per cent of the total power is used in the lamp proper, Whereas with a lamp which consumes over all 218 watts the percentage of power consumed by the lamp is only 42 lper cent.

In my description of the lamp 'I have referred only to the combination of a quartz mercury va.- pour lamp and lament lamps but I do not limit the scope of this invention to such a combination;

5 I may use other forms of lamps giving the required amount of ultra violet rays which when used in combination with filament lamps securev approximately the same complementary series of radiations with a surplus of short Wave component requiring selective ltering.

What I claim is:

1. A lighting unit comprising a source of ultraviolet radiation and a screen of fused silica, the.

arc arranged so that the heat generated in the resistance induces a circulation of cooling air within said screen.

3. A lighting unit as dened in claim 2, in which there is also a filament lamp within the screen.

4. A lighting unit which comprises a plurality of complementary light sources which together give a spectrum extending over the range of daylight, including the ultra violet, the light sources being so selected and proportioned in intensity as mutually to compensate for their respective deilciencies in spectral range, and means substantially enclosing said light sources comprising a screen of translucent silica, having bubbles, glaze and thickness regulated to absorb a relatively very large proportion of the radiation in the objectionable far ultra violet part of the spectrum and to transmit a relatively large proportion of the beneficial near ultra violet part of the spectrum.

RICHARD ARTHUR SURTEES PAGET.

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