Fluorescent Luminaire With Circular Heat-exchange Louver

Abstract

A luminaire containing one or more fluorescent tubes is provided with a housing in the form of a closed-end trough having a generally planar back surface with one or more ventilating air exhaust louvers therethrough. A light-transmitting front surface is provided with apertures therethrough for the passage of ventilating air into the luminaire, each louver in the back surface being comprised of a plurality of concentric rings of apertures, each aperture being provided with a superimposed vane disposed at an angle with respect to the plane of the louver, whereby the louver openings are substantially obscured by the vanes from a viewing angle near normal to the plane of the louver and the majority of the louver openings are substantially obscured by the vanes from any viewing angle from the front of the luminaire. The apertures are either arcuate or linear.

Description

BACKGROUND OF THE INVENTION

Fluorescent luminaires are often provided with a means for circulating ambient air through the body of the fixture and venting the lamp and ballast heat out of the top of the fixture housing. It has been established that the photometric efficiency of the lamps, and hence the fixture, is greatly reduced if the lamp temperature and the ballast temperature are allowed to increase beyond the design operating temperature.

It is current practice to provide an ambient air inlet through or around the light-transmitting element of the fixture, and to allow the air to move by convection through the fixture body to pick up component heat and carry it out through a louver in the back (or top) of the luminaire. Such louvers are usually in the form of a row or succession of closely-spaced apertures comprising elongated, parallel cutouts. The openings allow some measurable loss of light from the fixture, and therefore represent an optical efficiency loss, as well as forming a visually apparent dark spot within the luminaire when viewed from the light-emitting face of the luminaire. To reduce these effects, the apertures are often provided with integrally-formed parallel blades set at an angle with respect to the plane of the apertures. The blades serve to reduce the light loss from the fixture, and also reduce the apparent dark area of the louver as seen from an angle normal to the plane of the fixture back, but still show a dark area when viewed from an angle parallel to the plane of the louver blades.

The object of this invention is to provide a luminaire with a heat-exchange louver that has apertures substantially obscured by a system of vanes when viewed from any angle in front of the luminaire, thereby maintaining an adequate flow rate through a louver which is visually unobtrusive within the luminaire.

SUMMARY OF THE INVENTION

The object of the invention is achieved by a luminaire having a housing in the general form of a closed-end trough having a generally flat back surface of thin material, such as sheet metal, one or more fluorescent light sources disposed within the housing, a generally planar light-transmitting front surface having a means for venting ambient air into the luminaire, and a louver in the back surface of the housing having a number of concentric, arcuate apertures and partially obscuring vanes are formed therein.

The louver is comprised of a concentric series of arcuate apertures in the form of concentric, interrupted rings. The material forming the louver is a portion of the back surface of the luminaire housing, and the apertures are created by shearing one edge of each arcuate aperture from the plane of the parent sheet material and displacing the sheared edge away from the plane of the parent material to form a canted vane substantially spanning the width of the aperture and forming a generally cylindrical opening between the displaced sheared edge and the edge of the parent material. In an alternate embodiment, the apertures themselves are linear and arranged in concentric rings.

When the louver so formed as a number of concentric apertures and integral blades is viewed from an angle normal to the plane of the louver, the blades serve to substantially span all of the apertures, obscuring the openings from direct view. Similarly, the majority of the louver apertures are obscured from any viewing angle possible from the front of the luminaire.

Experimentation has shown that an open cross-sectional area characteristic of a given conventional, parallel-blade louver can be formed in accordance with the invention so that the visible dark area that can be seen from any angle in front of the luminaire is approximately one-third that of the conventional louver, while providing improved air flow and optical efficiency and significantly improved uniformity in appearance.

Although many variations of the concentric arcuate louver are possible which represent improvements over straight parallel-blade louvers, experience has shown that one embodiment is functionally preferred. That embodiment comprises a louver wherein the outer edge of each of the arcuate apertures is sheared from the parent material of the luminaire housing, leaving the inner edge attached in the plane of the parent material, and wherein the sheared edge of each arcuate aperture is displaced away from the plane of the parent material in a direction into the luminaire housing, towards the light source.

This preferred arrangement most easily accepts air from a large area within the luminaire and collects the heated air as it passes through the louver into a single column or chimney that tends to maintain the temperature of the column outside the luminaire and thereby enhances the effectiveness of convective pumping. In addition, the photometric properties of the preferred embodiment are superior in that the greatest amount of both diffuse and specular reflection from the louver blades are retained within the luminaire wherein the blades project into the luminaire housing.

A nearly ideal geometry for air flow in combination with optical efficiency is one in which each aperture has an open width dimension in the plane of the parent material approximately equal to the flat width of the parent material between adjacent apertures, in which the aperture also has its open width dimension approximately equal to the height of the opening created by the displacement of the sheared edge of the aperture away from the plane of the parent material, and in which the blade formed by displacement of the sheared edge is at an obtuse angle with respect to the plane of the parent material.

In a typical luminaire installation, the luminaire is installed in a horizontal plane so that the back surface of the housing is the top of the luminaire, and the light-transmitting element is the bottom surface facing into the room that is being illuminated. The luminaire, when used as a heat-exchange device, serves to at least partially exhaust air from the room, through the bottom surface of the luminaire into the fixture housing where the air can cool the luminaire components, and then through the louvers in the top surface of the luminaire to exhaust the heated air into a plenum above the room ceiling.

In operation, the invention serves to effectively scavenge the hottest air within the fixture by drawing from all directions along the plane of the uppermost surface. The hot air is then vented in the form of a concentrated column most capable of efficient convention. The louver apertures through the luminaire housing are totally obscured when viewed from directly beneath the luminaire and, similarly, the apertures are substantially obscured when viewed from any angle beneath the luminaire, thereby providing exceptionally efficient heat exchange performance and at the same time providing an improved uniformity of brightness visible from beneath the luminaire.

DESCRIPTION OF THE DRAWINGS

This invention may be more clearly understood from the following detailed description and by reference to the drawings in which:

FIG. 1 is a perspective view of a preferred embodiment of the luminaire as viewed from beneath, with the light-transmitting element removed to show the interior of the luminaire;

FIG. 2 is an enlarged perspective view of the louver of FIG. 1;

FIG. 3 is a cross-sectional view of the luminaire, showing typical air flow paths and light reflection properties;

FIG. 4 is an enlarged sectional view of the embodiment of FIG. 2 taken along lines 4--4 of FIG. 2; and,

FIG. 5 is a perspective view of a polygonic adaptation of the arcuate louver embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Now referring to FIG. 1, a luminaire 10 may be seen with the conventional grid or diffuser removed for purposes of clarity. The luminaire 10 includes basically a channel-shape pan member 11 having a pair of end plates 12 and 13 and a rear face 15 of the pan 11. Longitudinally mounted in a pair of sockets 20 and 21 are a pair of fluorescent lamps 22 and 23. Mounted on the rear wall 15 of the luminaire is a ballast 24 for the lamps. The lamps 22 and 23, as well as the ballast 24, constitute substantial sources of heat energy since approximately 80 percent of the electrical energy used by the luminaire is converted to heat and the balance into light which is directed downward through the open face of the luminaire. The heat generated within the luminaire must be removed for efficient operation of the lamps 22 and 23 and ballast 24 and room heat likewise must be removed. The covering for the lamps 22 and 23 at the bottom of the pan 11 is a grid or diffuser structure shown in FIG. 3. Heated room air is free to pass up into the luminaire and, if given proper venting in the rear face 15, passes through the luminaire over to the space above and, in the process, cool the lamps 22 and 23 and particularly the ballast 24. Where a diffuser is used below the lamps which are closed, an air handling groove represented in the drawing as slot 25 extends across one end of the luminaire 10. Preferably, this slot 25 is adjacent to the end holding the ballast 24.

Venting of the luminaire 10 is achieved through the louver, designated generally 26, made up of a pair of concentric segmented openings 30A-D and 31A-D. In the embodiment of FIG. 4, the numbers 30A-D are equally spaced around in a circular array of approximately 51/2 inches in diameter while the inner array 31A-D is approximately 3 inches in diameter. In a typical installation, the louver 26 comprises approximately 11 square inches of throat area which provides adequate cooling at static pressure differential of only 0.05 S.P. H.sub.2 O between the front and rear of the luminaire.

The details of the louver of FIG. 1 are more apparent in FIG. 2. In FIG. 2, it may be seen that the rear face 15 is made of thin sheet metal, for example, sheet steel, and the louver 26 and each of its openings is formed by stamping arcuate vanes 30A-D and 31A-D from the planar surface 15 in accordance with techniques well known in the metal piercing and stamping arts. In this case, the vanes 30A-D and 31A-D have integral surfaces which are generally angular with respect to the plane of rear face 15 as shown in FIG. 4 and present radially extending openings. The louver of FIG. 2 has a pair of vents opening in each of the four directions. The flow of air through the louvers tends to be towards a common central point of the louver assembly 26. The view of FIG. 2 is a louver as would be seen typically from below in the absence of any diffuser or grid on the luminaire. Note that approximately one-third of the total opening area is visible to the viewer.

The air handling and photometric properties of the louver of this invention are best shown in FIG. 3, which is a transverse section through a typical luminaire with eggcrate diffuser. The luminaire includes a pan 40 having a front step 41 in which eggcrate diffuser 42 is positioned below a pair of lamps 43 and 44. The luminaire of FIG. 3 is designed for flush mounting in a ceiling 45 in a manner which is well known in the art. Given the type of eggcrate diffuser shown in FIG. 3, air is free to enter the luminaire throughout its entire box surface and the air flow around the simple lamp 43 is represented by arrows. Positioned above the lamps 43 and 44 are a pair of louvers 50 and 51 with the first of the configuration shown in FIG. 2 and the second of an alternate configuration. In this case, it is noticed that air entering the diffuser 42 is swept past the lamp 43 and upward in a concentrated manner to the louver 50 in a form of vertically extending column of air formed like a chimney. The arrangement of the vanes making up the louver 50 tend to sweep the air past the relatively high temperature ballast 53 which is shown secured to the back wall 54 of the luminaire. This sweeping action of air through the louver 50 has been found in practice to produce approximately a 25 percent increase in air flow through the luminaire at the same static pressure between the front and rear of the luminaire as compared with the conventional aligned louver of the same cross-sectional area. Inasmuch as the static pressure across the luminaire is not controllable by the lamp designer, the increase air flow of the same static pressure is desirable. Typically, a luminaire having room temperature +2.degree.F air flow in the range of 25-75 cfm as compared with static condition results in approximately a 25 percent increase in light output because of the lower operating temperature of the lamp (air flow at room temperature, a plus approximately 20.degree.F).

It should be noted that the louver 51 differs from louver 50 in that the vanes are formed and extended outward or upward from the luminaire as compared with louver 50. In some luminaire designs, maximum unobstructed internal volume is required and then the arrangement similar to louver 51 is recommended. Note that the direction of flow of air is the same in both louvers (inward) but the vane direction is rearward. Both types of louvers are illustrated side-by-side in FIG. 3 for easy comparison although luminaires normally will have both louvers of the same form.

The recommended positioning of louvers of this invention in respect to lamps is illustrated in FIG. 3 with the lamp 44 directly under the louver 51. Considering the center of the lamp 44 as the light source, a number of ray patterns appear in the drawing. In the transverse plane of FIG. 3, all of the light emitted from source 44 is reflected and none passes through the louver 51. It must be recognized that the lamp 44 is elongated and light energy at acute angles along the lamp will tend to pass through the louver and be lost, however, since only approximately one-third of the total of the open area of louver 51 is visible from any viewing angle beneath the luminaire, a minimum of open area is presented to the lamp 44 as well.

Optimum dimensioning of the louvers is illustrated in FIG. 4 which shows a section along line 4--4 of FIG. 2. The louvers all extend at an angle A with respect to the plane of the housing. This angle has been determined to greatly affect the air handling capacity of the louver. As indicated above, the desire is to have the air swept past the heat producing elements of the luminaire and leave the luminaire with a degree of concentric inward flow to form the rising column of air or chimney shown by the dash-dot line in FIG. 3. We have found that vanes having a nominal angle A of 30.degree. meet this requirement and at the same time, meet a second optimizing relationship. It is desired that the air passage through the back 15 provide a minimum of turbulence and, if possible, no constrictions. We have found that three critical dimensions are involved. In this case, the outlet throat of louver 30 is designated B, while the inlet throat transverse dimension is designated D. The average length of the passage through louver 30 is a function of the spacing between rows and louvers and is designated C.

We have found that optimum handling through louver in accordance with this invention is achieved when the condition B .apprxeq. C .apprxeq. D occurs. That is to say, where the inlet, outlet and throat are equal in cross section. This occurs when the angle A approximates 30.degree. and the spacing between louvers is at least equal to B, C or D. The angle A may be varied from the optimum 30.degree. by approximately plus or minus 5.degree. without significant degradation or performance of the louver. The value of C may be greater than either B or D without decreasing the efficiency of the louver. This relationship appears in FIG. 5 which is used to illustrate that the vanes need not be curved as shown in FIG. 1 and 2. The circular array of straight vanes as shown in FIG. 5 provides the same chimney effect for air handling and minimum black area when viewed from the normal viewers angle below the luminaire. It again prevents only one-third visible open area in worst condition. From the foregoing, it may be seen that we have by careful analysis of the conventional venting louvers for lighting systems determined that through a change in arrangement and dimensions of the vanes, an increased air handling capacity in the order of 25 percent may be affected and at the same time improve the visual effect of the louvers.

As an ancillary and unforeseen improvement, we have also discovered that the louver of this invention tends to break up sound wave patterns entering the luminaire and passing through the louver to the chamber behind. This results in reduction of room-to-room sound transmission when the region above the luminaire is common to more than one room. Room-to-room sound transmission is undesirable, of course, and this configuration of louver as compared with prior art has demonstrated between 10 percent and 15 percent sound reduction transmission. This reduction in sound transmission is still in the presence of increased air handling capacity as described above.

It is recognized that following the teaching of this invention, one could, through minor changes within the scope of the teaching, produce variations which carry out the substance of the invention while having minor difference in detail. Therefore, the monopoly afforded by this patent shall not be restricted to the foregoing specific embodiments but instead by the invention as described in the following claims and their equivalents.

Claims

We claim:

1. A luminaire comprising:

an elongated housing member including side walls, a back wall and a light-transmitting front wall;

at least one fluorescent tube positioned in said housing to emit light through said front wall in said housing;

a vent in the back wall of said housing, said vent being positioned to allow air flow from the front face of the housing past the fluorescent tube and out through the back wall of said housing;

said vent comprising a plurality of integrally formed louvers arranged in a circular array with air passage being from the inside of said housing to the outside substantially inward towards the center of the circular array.

2. The combination in accordance with claim 1 wherein said vent comprises a plurality of concentric arrays of louvers.

3. The combination in accordance with claim 1 wherein said louvers are formed by displaced metal of said back wall extending inwardly into the housing at an angle in the order of 30.degree..

4. The combination in accordance with claim 1 wherein said louvers have an inlet throat displaced from the plane of said back wall a distance substantially equal to the transverse dimension across the louver in the plane of the back wall.

5. The combination in accordance with claim 4 wherein the said vent comprises a plurality of concentric louvers wherein adjacent louvers of different circles are spaced at least a distance equal to the width of the inlet throat and the transverse dimension of the louvers of the next outer circle of louvers.

6. The combination in accordance with claim 1 wherein said luminaire includes ballast means secured to said back wall and positioned wherein air passing through at least one of the louvers of said vent is swept past the ballast.

7. The combination in accordance with claim 6 wherein said vent is positioned along the length of said housing adjacent to said ballast.

8. A fluorescent luminaire for central horizontal mounting in a ceiling and including

an air passage between the space below and above the ceiling;

said luminaire comprising an elongated housing including a substantially planar back wall, a pair of side walls and a front light-transmitting face including at least one air inlet portion, at least one fluorescent lamp positioned within said housing;

said back wall of said housing including at least one vent positioned adjacent to the fluorescent tube and spaced along the length of said housing from at least a portion of the air inlet of the luminaire front face;

said vent comprising a circular array of louvers formed from metal displaced inwardly into said housing from said planar back with the air passage between the inside and outside of said luminaire through said louvers extends generally inwardly of said circle whereby air passes in through the inlet of the front face along at least a portion of said fluorescent lamp and out through said louvers in a generally chimney-like column as it leaves said louvers.