Shielded luminaire

Abstract

An improved radiation shielded luminaire utilizing gas discharge lamps. Shielding of radio frequency radiation is provided by a grounded superimposed screen and louver assembly. Additional shielding around the cathode area of the lamp shields radiation in the frequency ranges of x-ray and infrared radiation.

Description

BACKGROUND OF THE INVENTION

The present invention relates to luminaires having gas discharge type light sources and, more particularly, to an improved shielding arrangement which will suppress undesirable electromagnetic radiation while transmitting light in the frequency range of natural daylight.

It has been known for some time that gas discharge lamps such as fluorescent, mercury and sodium vapor and other similar lamps produce and emit electromagnetic radiation in the radio frequency (RF) spectrum and that such radiation causes interference with radio and other electronic measuring, testing and communicating equipment. More recently, it has become known that such radiation produces biological responses in plants. It is also believed to have an effect on animals and human beings by affecting the endocrine and central nervous systems. These biological effects are exceedingly complex and appear to involve an interplay of radiation in a number of different frequency ranges. One conclusion now evident is that natural light is a very important factor affecting life on earth and that artificial light sources should approach natural daylight in spectral distribution and intensity as closely as possible. This means that other kinds of radiation present in artificial light sources such as gas discharge lamps should be shielded since it may have an adverse effect on life as a form of radiation pollution. Radiation shielding heretofore used in gas discharge lamps and luminaires to prevent interference with electronic equipment is not completely adequate to prevent unwanted biological responses because of the wider frequency range of the radiation involved which requires shielding. Also, the shielding should not prevent the transmission from the luminaire of beneficial radiation found in natural daylight such as ultraviolet when the full-spectrum lamps, now commercially available, are used for illumination.

Accordingly, it is an object of this invention to provide an improved luminaire radiation shielding arrangement that will suppress unwanted radiation in a wide frequency range but not attenuate radiation in the frequency range of natural daylight.

Another object of the invention is to provide a shielded luminaire construction that is relatively simple, inexpensive to manufacture and which can be easily applied to luminaires of conventional construction.

Further objects and advantages of the invention will become apparent as the following description proceeds.

SUMMARY

Briefly, in accordance with the invention a luminaire is provided with a housing having an opening through which light from the lamps passes. The opening is covered by a louver assembly comprising crossed fins forming a plurality of open cells through which light passes. Supported on the louver assembly on the lamp side is a conductive screen having mesh openings large enough to pass a substantial amount of light but smaller than the louver cells. The housing, louver assembly and screen are grounded to provide RF shielding of the enclosed lamps over an extended frequency range. Visible and ultraviolet light passing directly to the illuminated area through the openings in the screen and louver are not attenuated. The louver also provides glare shielding of visible light in the usual way. Shielding of unwanted radiation in the infrared and x-ray frequency ranges is provided by additional shields encircling the cathodes of the lamps.

For a better understanding of the invention, reference should be made to the following detailed description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a luminaire embodying the shielding construction of the present invention.

FIG. 2 is a partial sectional side view of the luminaire of FIG. 1.

FIG. 3 is a perspective view illustrating constructional details of the louver assembly.

FIG. 4 shows the screen used in the shielding construction.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

Referring to FIG. 1, there is shown by way of an example a fluorescent lamp luminaire of the recessed type adapted for a flush mounting on a ceiling. The luminaire comprises a housing 10 formed of a suitable electrically conducting material such as aluminum. Illumination is provided by one or more tubular fluorescent lamps, one of which is shown and designated by the number 11. Mounting sockets 12 carried on the housing sides 13 receive the lamp pins 14 which are energized from a power source 15 through the usual ballast and starting equipment (not shown). In order to provide illumination having in the visible light range a spectral composition similar to daylight a full-spectrum fluorescent lamp is preferably used. Such lamps are now commercially available and the construction of such a lamp is shown, for example, in U.S. Pat. No. 3,670,193, issued June 13, 1972. Such lamps emit, in addition to visible light, middle and rear ultraviolet (UV) in about the same ratio as found in natural daylight and the emission of such UV is believed to be important from a health standpoint where the lamps are used for general illumination.

The housing 10 has a bottom opening 16 through which light from lamp 11 passes into the illuminated area. The opening is covered by a louver assembly 17 of the so-called egg crate type, the construction of which is shown in FIG. 3. As shown the louver assembly comprises a plurality of perpendicular crossed fins 18 and 19 secured together in any suitable manner to form a rigid construction. Light from lamp 11 passes through cells 20 formed by the crossed fins 18 and 19. The fins control the light distribution from the lamp in the usual way by cutting off direct light from the lamp 11 at so-called glare angles exceeding a predetermined angle with respect to the vertical. This is illustrated in FIG. 2 where a light ray A from lamp 11 passes through a cell 20 to the illumined area below. On the other hand, a light ray B leaving the lamp in the glare angle range is intercepted by fin 19.

For convenience in servicing the luminaire, the louver assembly 17 is suspended on pivots 21 so that it can be swung down on one side to give access to the interior of the luminaire.

As pointed out above, gas discharge lamps are known to generate and emit electromagnetic radiation in the range of the Hertzian or radio waves and for the reasons stated, it is desirable to prevent such radiation by suitable shielding. According to the invention, shielding is provided that is effective over an extended frequency range. A part of such shielding is provided by the louver assembly. To this end, the fins 18 and 19 are formed of an electrically conductive material such as aluminum and the assembly is electrically connected to ground potential in any suitable manner as by a connection designated by lead 22.

The attentuation of radio waves in a given frequency range passing through a grounded grid such as that provided by the crossed fins 18 and 19 is a function of the grid size. The control of visible light distribution from the lamp is predetermined glare angle range as explained above is also a function of grid size. Thus, if the grid size is fixed by light distribution considerations, the louver assembly will not adequately attenuate radio waves in the higher frequency ranges where proper shielding is also considered important. Therefore, to give more adequate radio wave shielding in a higher frequency range additional shielding is provided as will now be described.

Supported on the top of the louver assembly so as to cover completely the housing opening 16 is a wire mesh screen 23. The screen is formed by crossed strands 24 and 25 of electrically conductive material. The construction may, as shown, in FIGS. 1 and 4 be a woven aluminum wire similar in construction to ordinary window screen. The screen is electrically connected to ground potential in any suitable manner, the connection being designated by the lead 26. Also grounded is the luminaire housing 10, this connection being designated by lead 27.

The mesh openings 28 of screen 23 are of sufficient size to permit passage of light therethrough from the lamp 11 to the illuminated area with reasonable efficiency. They are, however, as shown, considerably smaller than the size of cells 20 in the louver assembly 17. For that reason, the screen 23 attenuates radio waves in a higher frequency range than the louver assembly 17. Acting together, the louver assembly and screen provide effective shielding of radio waves over an extended frequency range. This permits optimum design of the louver assembly with respect to its light shielding function without sacrificing efficiency of the radio wave shield. By way of an example, good results have been obtained applying the invention to a luminaire having four 40 watt fluorescent lamps and having an opening 16 of 8 square feet. The size of cells 20 was 1.75 .times. 1.75 inches square and the cell depth was 1 inch. The screen 23 used was woven aluminum screen having approximately 64 mesh openings per square inch.

Because the screen 23 is made of a highly reflective material it reflects the ultraviolet as well as the visible light from the fluorescent lamp with good efficiency and without spectral distortion as would be the case if a dark colored material such as copper were used.

Mounting the screen 23 above rather than below the louver assembly has several advantages. First, the conductive screen is held by gravity in firm contact with the conductive fin members 18 and 19 maintaining good electrical contact for uniform ground potential distribution. Secondly, mounted in this position, any glare caused by reflection of light from the lamp by the screen, as indicated, for example, by ray C in FIG. 2, will be shielded by the louver assembly.

In addition to radiation in the radio wave frequency range emanating from the lamp, there is additional radiation from the electrode area of the lamp which should be shielded. For this purpose, there are provided cathode shields 29 and 30 which are mounted on the envelope of the fluorescent tube adjacent the ends so as to encircle the cathode area. These shields may be made by wrapping lead foil around the outside of the tube envelope, the foil being held in position by an adhesive coating thereon. Cathode shields formed in this and other suitable ways are disclosed in U.S. Pat. No. 3,767,957, issued Oct. 23, 1973 and assigned to the same assignee as the present invention. By making the cathode shield of a high atomic number material such as lead they will absorb electrode radiation in the frequency range of x-rays as well as radiation on the infrared range both of which should be excluded from the luminaire light output to avoid radiation pollution.

In view of the foregoing, it will be apparent that there has been provided a luminaire that is relatively free of radiation pollution while emitting the desired radiation of the natural daylight type, including the ultraviolet which is produced by full-spectrum lamps. The ultraviolet component of such light is preserved by the use of a highly reflective radio wave screen. It is noted here that the use of a light control element utilizing a solid light transmission material such as glass absorbs the ultraviolet and is undesirable for that reason when used with full-spectrum lamps. It will also be apparent that the combined screen and shield construction is simple, inexpensive, and can be easily applied to luminaires of the conventional type.

While there has been shown what is considered to be a preferred embodiment of the invention as applied to a luminaire utilizing fluorescent type gas discharge lamps, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.

Claims

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A shielded luminaire comprising:

a housing formed of conductive material having a light-emitting opening therein,

a gas discharge type lamp mounted within said housing so as to project light through said opening,

a light shielding louver assembly extending over said opening, said assembly comprising a plurality of crossed fins formed of conductive material which form cells through which light from said lamp passes,

a mesh screen formed of crossed conductive strands extending across said opening between said lamp and said louver assembly, and

connecting means electrically connecting to ground potential said housing, louver assembly and screen,

the area of the screen mesh being sufficient to permit passage of light therethrough but smaller than the cell area of the louver assembly whereby RF radiation from said lamp is attenuated over an extended frequency range by action of the grounded screen and louver assembly while permitting passage of light from said lamp through the screen mesh and louver cells into the area illuminated by said lamp.

2. The shielded luminaire of claim 1 wherein the screen is supported by the louver assembly.

3. The shielded luminaire of claim 1 including radiation shields extending around the cathode areas of the lamp.

4. The shielded luminaire of claim 1 wherein the conductive strands of the screen are formed of a highly reflective material which will reflect light from the lamp without spectral distortion.

5. The shielded luminaire of claim 4 wherein the conductive strands of the screen are formed of a material comprising aluminum.