US2366216A - Shield for mercury vapor lamps - Google Patents

Description

Jan. 2, 1945. J. A. ROBERTS SHIELD F OR MERCURY VAPOR LAMPS Filed Feb. 14, 1942 m mm M WA M m Patented Jan. 2, 1945 SHIELD FOR MERCURY VAPOR LAMPS John A. Roberts, New York, N. Y., assignor of onehalf to H. Dorsey Spencer, New York, N. Y.

Application February 14, 1942, Serial No. 430,939

4 Claims.

This invention relates to devices for improving both the efllciency and the light values of various illuminating devices, and particularly those in which mercury vapor is employed.

The efliciency of mercury vapor lamps, and

mercury vapor is employed to produce the ultraviolet radiation which activates the fluorescent lining of the lamp tube, is affected considerablyby changes in temperature of the tube or bulb wall of the lamp. For highest efliciency it has been found that the bulb wall temperature of fluorescent lamps should be stabilized within the range of from 100* to 120 F. and that marked variations from this range will cause a sharp drop in rescent light has been produced by a newer lamp called "soft white," but even the purpose of this lamp has been largely defeated by its bad color particularly of those fluorescent lamps in which distortion.

A simple and inexpensive solution of the problem caused by excessive coldness of fluorescent daylight is, therefore, an incidental object of the light efllciency. This drop in efllciency is dueto (a) Condensation of mercury vapor within the lamp at lower temperatures, and V (b) Increased vapor pressure at'higher temperatures. t

One of the objects of the presehtimieffiion is to improve the overall efllciency of mercury vapor lamps, and particularly of mercury vapor lamps of the fluorescent type, by preventing marked variations in the bulb wall temperature. Fluorescent lighting is rapidly replacing other forms of artificial illumination because of its economy of operation and because it provides a whiter and more optically efficient light than the light produced from a tungsten filament. Fluorescent illumination as thus far developed has, however, certain peculiarities and objectionable characteristics which it is the purpose of the present invention to overcome in a simple and inexpensive way.

The sensitiveness of the mercury vapor and fluorescent lamps to temperature changes and particularly to drafts has been referred to hereinabove and, as above suggested, the principal object of the present invention is to protect such lamps from marked variations in the bulb wall temperature and thus maintain a high efficiency of operation. However, one of the objectionable characteristics of fluorescent illumination, as it has so far been developed, is that the light from what is called the fluorescent daylight lamp is admittedly a very cold appearing light, generally too cold to be acceptable for use in the home or in other places where true daylight color values are not the primary object. To offset this objection, fluorescent lamp manufacturer have modified the so-called daylight" lamp by producing another lamp designated as white. This lamp has also proved to be still unpleasantly cold and, therefore, more recently a still warmer fluo- .present invention.

the invention aims to provide a simple and comaratively inexpensive combined temperature stabilizing shield and light filter, preferably in the form of a sheath which can be slipped over the lamp tube and which will serve both to protect the tube against marked changes in the bulb wall temperature and also, where desired, to produce the desired light correction or color effect.

an important feature of the invention is the provision of a light weight, inexpensive and easily applied combined temperature stabilizing covering for tubular lamps, and particularly :for fluorescent lamps, which is formed of translucent elastic sheet material so conformed to the lamp tube with which it is to be used as to be selfsupporting when in temperature stabilizing relation thereto and yet having the greater part of its surface so spaced from the lamp tube as to provide ventilation and thus overheating. A further important feature of the invention is the formation of the greater part of the sheath or shield or fluted elastic material so conformed to the lamp tube that the ridges of the flutes will engage the tube and assist in maintaining the sheath in proper relation thereto. Among the advantages of this last-mentioned construction are the provision of passages for ventilating air between the greater part of the sheath or shield and the tube and the fact that only a very small part of the surface of the sheath or shield is actually in contact with the tube. Overheating of thetube is thus prevented by the moderate circulation of the combined insulating and heat removing air between the sheath and the tube and overheating of the sheath or shield is also prevented by the relatively small amount of surface of the sheath or'shield brought into heat-conducting contact with the lamp tube.

Other objects and important featuresof the invention will appear from the following descrip tion and claims when considered in connection with the accompanying drawing, in which Figure 2 is a transverse section through the structure shown in Figure 1;

Figure 3 shows a slightly modified form of the sheath illustrated in Figures 1 and 2, the modification being designed to adapt the sheath for use'with fluorescent lamps in which the lamp tube is located close to the reflector;

Figure 4 is a modified form of the sheath for use with the ordinary cylindrical fluorescent lamp tube;

Figure 5 shows still another modification of the sheath suitable forv use with cylindrical fluorescent lamp tubes;

Figure 6 shows a slight modification of the sheath construction shown in Figure 5, and

Figure '7 shows a modification of the fluorescent lamp tube section to permit the use of a cylindrical form of sheath without spacing ribs or lugs.

In the illustrative embodiment of the invention shown in Figures 1 and 2, the fixture which supports the fluorescent lamp tube 2 comprises end sockets. and 6 for thetube; said sockets being carried upon a reflector structure 8 supported from the ceiling, or other suitable part of the room to be illuminated, by hollow rods iii and I2 through which the electrical connections to the lamp are made. ihe sheath i4 shown in Figures 1 and 2 is made of translucent elastic plastic sheet material, preferably having a very low coemcient of light absorption, and this sheet material is pleated, preferably to form longitudinal flutes. As herein shown, the longitudinal flutes of the sheath ware iormed with comparatively sharp ridges, but it will be understood that the invention is not restricted to the particular flute shape here shown or to a comparatively large number of flutes shown and that,

any other form of flute which will provide channels It for insulating and ventilating purposes may be employed. One advantage of the comparatively sharp ridges showninthe illustrated sheath M isthat the amount 0! the surface of the sheath l4 that is brought-into actual contact with the tube 2, even with the large number of flutes shown, is comparatively slight thus preventing much conduction of heat directly from the tube 2 to the sheath ll.

When a fluted sheath, such as shown in Figures 1 and 2, is to be used with a fixture in which the tube is located in close proximity to the reflector, as, for example, in the structure shown in Figure, 3 in which the curved reflector I8 is spaced only a short distance from the upper surface of the tube 2, the fluting maybe omitted from that part of the sheath which is to cover the part of the tube 2 closest to the reflector it, this partof the sheath, asshown, being formed of smooth overlapping margins and 22, preferably cemented together to complete the tubular form of the sheath. I

It will be seen that a sheath such as shown in Figures 1, 2 and 3, which is made up of translucent elastic plastic sheet material, pleated into longitudinal flutes asshown, will, when formed into a complete tube, adjust itselfreadily to fluorescent lamp tubes of slightly dlfierent'diameters and that it will provide insulation for the lamp tube against sharp changes in the temperature of the surrounding atmosphere, and particularly against draughts, by reason of the air which is in the channels it and that-these channels 16 will also provide for a moderate circulation of air therethrough to carry away any excess heat.

that might tend to accumulate by reason of the insulation thus provided, thereby preventing overheating of the tubes.

In Figure 4 is shown a modified embodiment of the invention which will provide ventilation to prevent overheating of the tube but which may require a somewhat thicker plastic sheet to give the same degree of insulation, by reason of the lackof the closely spaced air channels l6 and by reason of the more extensive contact of the surface of the plastic with, the lamp tube. As shown in Figure 4, the sheath 24 is octagonal in form thus providing air channels 26. This sheath 24, like the sheath I 4, allows for some variation in the diameterbf the tube 2. such variation, if on the high side, causing a distor-" tion of the octagonal form or, in other words, a

, as continuous ribs, the sheath maybe formed as a continuously .extruded tube of the plastic of the sectional shape shown in Figure 5, thus avoiding the necessity for cementing together the overlapping or abutting margins of the sheet, as is done in the forms shown in Figures 2, 3, 4 and '7.

Byso proportioning the diameter of the sheath 28 to the diameter of the lamp tube 2 with which it is to be used that, when the sheath is eccentrically positioned on the lamp tube, as shown in Figure 5, the ventilating and insulating space 32 will be sufiicient to maintain the desired tube temperatures, then the fact that the part of the sheath adjacent to the reflector, that is, the part covering the top part ofthe lamp tube 2 is in immediate contact with the tube will not materially aifect-the desired overall result.

In the form of the invention shown in Figure 6,

which is a modification of the structure shown in Figure 5, the sheath 34 is shown, not as a complete tube completely surrounding the lamp tube 2, but as an elastic structure, open on the top side where the tube is more or less protected by the reflector of the fixture anyway, thi construction having the advantage that it maybe sprung over the lamp tube '2 without removing it from its fixture." It will be understood that this provision of an open side is not restricted to this form of the invention and that, if the plastic employed in making the sheath be sufiiciently elastic to form a self-sustaining sheath shape.

any form of the sheath of the present invention Figure '7 is made polygonal in cross section, the

illustrated lamp tube being shown a hexagonal in section. This permits the use of a cylindrical sheath 38 of a diameter which permits it to engage each of the apices of the angles of the hexagon. As will be seen, the curvatureof the sheath 38 away from the plane sides of the hexagon 36 provides the insulating and ventilating passages 40 between the sheath 38 and the tube 36.

From the foregoing description it will be seen that the present invention provides simple and comparatively inexpensive means for increasing invention, because of its comparatively low absorption of light and because of its high resistance to deterioration when subjected to the lamp heat and other conditions which are met with in the use of sheaths of the present invention with fluorescent lamps, is the plastic sold under the trade name 01 Plastacele.- Another plastic that has given very satisfactory results in use in sheaths embodying the presentinvention is one sold under the trade name of Lumarith.

be seen that, by reason of the ease with which it can be given any desired color, tint or shade, it lends itself readily both to color correction,

where necessary, and to the production of color eflfects in lighting, as, for example, in store window displays.

What is claimed as new is: -1. A temperature stabilizing covering for tubular lamps of the mercury vapor type comprising translucent elastic sheet material of substantially uniform thickness and sufficiently conformed to the shape of the lamp to be self-supporting thereon when brought into protective relation thereto, said covering enclosing all light radiating parts of the lamp tube which would otherwise be'directly exposed to atmospheric changes in the illuminated sp'ace and having lamp-engaging por- When Plastacele is employed as the plastic for use in making the sheath of the present invention, a colorless sheet of this plastic of the thickness required to give the desired elasticity and strength and shaped to form a sheath such as shown in Figures 1, 2 and 3 is estimated to have a light absorption factor of about 2%. If, therefore, a sheath of the form shown in Figures 1, 2 and 3 be constructed of colorless Plastacele of the aforementioned thickness and be used with a fluorescent lamp subjected to considerable variations in temperature of the surrounding atmosphere, it will be found that the light output of the lamp at low temperatures will be markedly increased and that there will be substantially no lowering of the output as compared with a bare lamp until the temperature of the surrounding air passes normal room temperature. It will thus be seen that for usual lighting conditions the use of the sheath of the present invention will increase the overall efiiciency of the fluorescent lamp and that only under abnormal conditions, that is, when the atmosphere surrounding the lamp is above normal room temperature will there be loss of emciency as compared with the bare.

tions thereof so construe ed and arranged that the major portion of the inner surface of said sheet material is only slightly spaced from the a lamp when in protective relation thereto but is provided with continuous longitudinally extending open-ended air channels between said lamp and said protective covering which serve not only for containing-insulating air but also for permit 7 ting heat-removing circulation thereof suflicient out the greater portion of its tube covering area and is so conformed to the lamp tube with which it is to be used that, when the covering is in protective relation thereto, ridges of the flutes engage .2 the tube throughout its light radiating extent "and form ventilating and insulating channels continuous from end to end thereof.

- 3. A temperature stabilizing covering according to claim 1 in which the elastic sheet material is moulded into a tube, the adjacent margins of the sheet being left unconnected whereby the tube may be sprung into covering position on the lamp. 7

v 4. A temperature stabilizing covering according to claim 1 in which the translucent sheet material is composed of a translucent plastic which,

when uncolored and of a thickness sufficient to provide the required self supporting elastic in the finished structure, has a light absorption coeflicient of only about two per cent of the rays passing directly therethrough.

JOHN A. ROBERTS.

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