US3098612A - Lighting fixtures - Google Patents

Description

July 23, 1963 E. PRICE ETAL LIGHTING FIXTURES Filed Sept. 18, 1958 5 Sheets-Sheet 1 M 6 ma W m/e m E om w r v 0 4 W. N G m m f Y B Filed Sept. 18, 1958 5 Sheets-Sheet 2 fail,

INVENTORS [o/so/v Pym: /5A4 Goooea July 23, 1963 E. PRICE ETAL 3,098,612

LIGHTING FIXTURES Filed Sept. 18, 1958 5 Sheets-Sheet 3 IN ENTORS fa/so R v/qr G I BY /s44c 00 644 Z nyo'v 9- w ow Array/vars Jul 23, 1963 E. PRICE Em. 3,098,612

LIGHTING FIXTURES Filed Sept. 18, 1958 5 Sheets-Sheet 4 INVENTORS [0/5 0 191: 6

BY 4844 Q 6000544 kayo July 23, 1963 E. PRICE ETAL LIGHTING FIXTURES 5 Sheets-Sheet 5 Filed Sept. 18, 195B FIG. 8

INVENTORS EDISON PRiCE ISAAC GOODBAR BY 7 ZZ/ ATTORNEYS United States Patent 3.698.612 LIGHTING FIXTURES Edison Price, 17 King St. New York, N.Y., and Isaac Goodbar. New York, N.\. (93-02 211th St., Queens Village 28, NJ.)

Filed Sept. 18. I958, Ser. No. 857,641 4 Claims. (CI. 240-4135) The present invention relates to lighting fixtures and more particularly to lighting fixtures which have the characteristic of being practically invisible when viewed at angles with the vertical axis of the fixture greater than a predetermined angle.

When lighting building lobbies. arcades. rooms. etc., it is often desirable to light certain objects or areas with direct or once reflected light from luminary sources while effectively hiding these sources from the viewer who is not directly or substantially directly under one of them. Many lighting engineers have attempted to accomplish this objective by bathing. reflectors and other similar means with only partial success and ofttimes at the expense of lost light.

The present invention provides a solution to this long existing problem. In accordance with this invention the light source which may hzoe practically any desired shape, is positioned in and has a definite relation to a light fixture having a particular shape. This light fixture is generally well adapted to be recessed in a ceiling although this is not essential. Further. it is preferred that the inner surface of this fixture should be a specular polished black surface to give the best re ults from an invisibility of light source standpoint and it should be assumed that a fixture having such a surface is being referred to hereinafter, although other surfaces may be used such as gold, etc. to give special desired eflects.

Such a fixture made in accordance with this invention will reflect a high percentage of the light from the light source onto areas beneath the fixture but will be virtually invisible to the vieucr looking toward the fixture from a greater angle as such viewer will only see that portion of the inside of the fixture which is dark. Thus the viewer will not see any reflection of the light source nor will he see any reflections from the area beneath the fixture.

It is a primary object of the present invention to pro vide such a light fixture which will have the foregoing characteristics.

It is another object of the present invention to provide such fixtures which have these characteristics and also provide good lighting economy.

It is still another object of this invention to provide such fixtures having a very low glare factor when viewed from normal angles of view.

Still further objects and advantages of the present invention will he recognized during a reading of the following description in conjunction with the accompanying drawings referred to, wherein:

FIG. 1 is a diagrammatic perspective view of a cutaway light fixture and light source wherein the outer surface of the light source is defined by a vertical plane therethrough revolved about its vertical axis;

FIG. 2 is a diagrammatic view similar to FIG. I wherein the light source has a generally horizontal cylindrical shape;

FIG. 3 is a diagrammatic vertical cross-sectional view through a light fixture and light source having a somewhat irregular surface contour;

FIG. 4 is a diagrammatic vertical cross-section through a light fixture and a light source of the spotlight or internal reflector type:

FIG. 5 is a modified form of FIG. 4 wherein the fixture is adapted for low ceiling use; and

FIG. 6 is a diagrammatic vertical cross-sectional view of a fixture of the present invention disposed below a light source comprised of a silvered bowl incandescent lamp having a reflector positioned concentrically therearound.

FIG. 7 is a diagrammatic side elevational view of a modified form of the invention showing its application in the case of cylindrical light sources.

FIG. 8 is a cross sectional diagram of the construction shown in FIG. 7.

FIG. 9 is a diagrammatic perspective view of the same construction.

As will be seen from a further reading of this description the foregoing figures are merely the diagrammatic illustrations of examples of fixtures that are designed around the particular light source 1 illustrated in accordance with the present invention and any other light source can be accommodated by following the teachings of this specification.

In general, the known light sources 1. i.e. the contour of the luminous surfaces thereof, have either of the followin g shapes: to) A surface of revolution about tical; or (b) A horizontal cylindrical surface havinga constant vertical cross-section.

an axis normally ver- In both of these cases the surface of the light source 1 and the inner surface of the light fixture 2 can be defined in plane coordinates to give the light fixture contour and light source placement of the present invention.

In the (a) case the axis of symmetry will be designated the y axis as in FIG. 1 and. since all cross sections containing it are identical. the x axis can be taken anywhere. perpendicular to the y axis. In particular cases. as it will be shown. a good choice of the .1" axis may greatly simplify the mathematical equations arising.

In some cases. especially if the y axis is not vertical. the limiting angle with y (above which only very low brightness must be seen) may change in ditferent directions. These special cases will be treated in due course.

In the case of cylindrical sources such as FIG. 2 the x and y axes may be taken in any plane.

In any of the situations considered. therefore. the shape of the source will be perfectly defined by a plane curve. and in general the shape of the reflecting surface will also be perfectly defined when its intersection with the plane of coordinates is known.

In the course of the present description. these reflecting surfaces will be defined as functions of the source shape and limiting angle, first in absolutely general cases and then more specifically as when the sources have other simple shapes.

Referring to FIGS. 1 and 3 wherein the contour of the light source 1 is a surface of revolution about the vertical or y axis it is first necessary to define this contour either graphically or analytically, by the equation:

Any coneavities in the light source 1 should be replaced with straight tangentially bridging lines. as in FIG. 3 at 1'.

Once the curve of the light source 1 is known it will be possible to determine at any of its points:

the reflecting surtangents 5. to the If this is achieved. the of the source will be al- Since we are always concerned with the extreme tangents, i.e. with tangents that do not intersect the source, whenever there is a concave part in the source 1 it must be replaced with straight tangentially bridging lines, as in FIG. 3, at 1'. Otherwise the tangents drawn from concave parts of the source 1 would each intersect the source. The desired curve will have, at each point P, a common tangent with a parabola inclined at an angle c from the vertical, having the focus at the point of tangency, and containing the point P, as shown in FIG. 3. As the point of tangency keeps moving along the curve 1, this parabola keeps changing continuously, generating the curve 2 which is, thus, very difierent from any single parabola. Referring now to FIG. 3, where X, Y is a point of the desired reflecting surface 2 and x, y, a point of the outline of the source, because of a well known property of the parabola, the sum (U-l-L) (where U is the distance from any point X, Y to a straight line forming an angle c with the x-axis and containing the origin of coordinates and L is the distance measured along the extreme tangent to the source, between the source and the reflector) must remain constant for each parabola of focus x, y. If the focus of the parabola moves along the curve 1, the length of travel of this focus, along the curve 1 must be equal to the increment of the sum (U+L). or, calling s the length of the curve measured from x= to the point of x, y, the sum (U+L+s) must remain constant. Calling this constant E, it is possible to write:

Looking at FIG. 3, it is possible to see that the distance U can be expressed as a function of the desired, and yet unknown, coordinates X and Y, and the angle 0:

(2A) U:X sin c-Y cos c also, these unknown coordinates X, F, may be expressed as functions of the known coordinates .r, y, and of the, yet unknown, length L:

are the horizontal and vertical projections of L.

Replacing 3A and 4A in 2A:

U=x sin c-y cos cd l 805 6 replacing 6A in 1A:

:csin c-y cos c+ +L+s=E replacing SA,

O X (11 2 laquation 4- ahovo and s: 1+( dz (4!) below) I! 4 in SA and 4A:

- J1 sine cosc+ l+ where E is a constant of integration, to be determined from desired initial conditions, making:

(4 FIB/1+ (3) and (4) then become:

and:

as well as:

(11) s, i wm -de If the light source 1 is defined only graphically, a tangent 5 thereto should be drawn from the point 0. This tangent 5 at the point of contact with the light source 1 will have the coordinates x y while its slope will give y and the length along the curve 4 from the y axis will be designated s Then:

+s +x sin c-y cos c Using (12) in Equations 5 and 6 and taking into account Equations 2, 3 and 4 a set of parametric equations (with x or another variable as an independent parameter) will perfectly define the reflecting surface. In some cases it may be found convenient to use several values of E for different portions of the reflecting surface, this can be done simply by repeating, as many times as required, the procedure just described.

This inner surface of the fixture 2 in turn defines in space a surface having the following property, as it is possible to prove mathematically:

Any visual line contained in a plane forming an angle c with the vertical which intersects the inner surface of the fixture 2 defined, will be reflected in a plane tangent to the line 5. Only one visual line forming the angle with the vertical will be reflected as tangent to the source 1 and all the other visual lines in the plane considered will be reflected in the plane of tangent but outside of the source 1 and will reach other points of the inner surface of the fixture 2. Also, all visual lines such as 42, contained in planes forming angles greater than c with the vertical will be reflected below the tangent line 5 and will thus not reach the light source 1.

When the inner surface of the fixture 2 is viewed from a comparatively large distance, as in a higher ceiling building where the viewer is beneath the fixture as a large distance, the visual lines such as 44, reach it as practically parallel lines. Accordingly they will all form the same angle L with the extreme bright rays 43, reflected at each point. The brightness of the inner surface of the fixture 2 will, for this reason, appear almost uniform. Also, any ray of light emitted by the light source 1 in any direction, such as 45, will be reflected into the useful zone at angles with the vertical smaller than c.

It is also possible to prove mathematically that all visual rays of light are reflected inside the fixture provided that the inner surface of the fixture 2 is prolonged downwards a sutficient distance to intersect the extreme tangent 6 to the light source 1 forming with the vertical the desired angle 0 and that no brightness outside of the fixture can be seen, directly reflected in any part of the fixture.

All of the foregoing is also true in the case of cylindrical sources when the fixtures are viewed from points such that the lines of sight lie in planes approaching the perpendicular to the source. This may be acceptable in many situations. When it is not acceptable other cylindrical reflecting surfaces, with generatrices perpendicular to those of the source will have to be provided. These surfaces can be designed by applying Equations 5 and 6 in planes parallel to the generatrices of the source.

To make this more understandable a practical example will be considered. FIGS. 7, 8 and 9 show the application of Equations 5 and 6 when the gcneratrices are perpendicular to the generatrices of the source as in the case of the most common cylindrical source at present in use, the fluorescent tube. If the fixture is to be viewed from planes such as 1: (plane of FIG. 8), approaching the perpendicular to the source 1, only the surfaces 2p are required. When this is not acceptable, i.e. when the fixture has to be viewed also from planes approaching the parallel to the source, or, in fact, from any other planes, other cylindrical surfaces Zq (FIGS. 7 and 9) with generatrices perpendicular to those of the source 1 will have to be provided. These surfaces can be designed by applying Equations 5 and 6 in planes parallel to the generatrices of the source, such as It (plane of FIG. 7).

Most standard reflector lamps at present available send their luminous output through an outside spherical surface, such as 11 in FIG. 4. Often the edges of these reflector lamps are of a toroidal shape, as shown in 12, FIG. 4.

The equation of the surface 11 in the system of coordinates shown (with the axes x and y passing through the center of the sphere) and the radius of the sphere taken as the unit of length, will be:

the parametric equations will be:

y sint (1 i) lx=oost or, calling:

then:

( w m vmfi=cosec t replacing this in (5) and including /z1r in E.

parametric equations perfectly define the desired curve.

If it is desired that no part of the source should be directly visible at angles larger than c, this curve has to be prolonged downwards until:

23 i=r-C if the angle b shown in FIG. 4 is: (24) b /21r-c or until:

In this last preferred case the lowest point P corresponding to the extreme point 7, cannot be the end of the inner surface of the fixture 2, as this would make possible the direct viewing from point v of parts of the source at an angle d larger than angle c which cannot be accepted. Therefore, in this case the inner surface of the fixture 2 must be continued downwards, in view of the edge portions 12 of surface 11 which are small circles of radius r. The parametric equations for this extension area:

where i.e. until the curve 2 intersects the straight line 52. This will prevent the viewing of any part of the source at angles larger than c.

In some lamps, surface 11 may end abruptly at points p. The corresponding equation for the curve, for

sin (t c)+cos U)-C)] cost and making: (30) 2K: /z1r+b-t sin (t --c)+cos (bc) (29) becomes: {X=sin b+K stc (t*c) sint Y cos bK see LKIAC) cost which are the parametric equations of a parabola with focus of coordinates:

q I: sin I) iy cos b and with its axis in the direction:

( /z1r+c The curve 2 is defined by the extreme tangents to the outline of the source 1. Looking at FIG. 4, it is clear that all tangents to the source 1, drawn from points below P, touch the outline of the source only on the circle edge portions of radius r and never on the spherical surface 11. Therefore, the reflecting surface 2, below P, is defined by Equations 27, 29 which define the reflecting surface as a function of only the portions 12, not taking into account the shape of the spherical surface 11. flected at the angle 6, any other ray originating at any other part of the source, including 11, will be always reflected below 0.

The shape of the inner surface of the fixture 2 can be simplified into a parabola in cases like the one shown in FIG. 6, where 14 is a silvered bowl lamp and 15 is a refiector. In this case the reflector 15 must be taken as the virtual source and, since it is concave, it reduces to the flat disc FF, the intersection of which with the plane of coordinates is the line FF.

The equation of this straight line is:

y=f( I4 2:

d1: 0 v"1+y' replacing in (5) and (6):

w l (34) l I'hlfl which shows that only one point in the whole line F-F If the extreme tangents to the portions 12 are recorresponds to the inner surface of the fixture 2 at the coordinates given by (34).

The points F, however, can be considered as circles of infinitesimal radius. lf the radius PF is taken as unit and the radius of the small circle in F is made r, then:

and, replacing in (S) and (6):

X:1+rcost +P 1+rt+sin n+1 cos {.sin c+r sin Leos t:

sin c+cot Leos c+coscc t Y r sin 1 I'3+l +rt+sin c-l-r cos Lsin c-t-r sin Lens sin cicot Leos c-l-coscc t and, when r:()

(Ed-l-Fsin (l sint cot t and if, for a certain value of t the curve must pass through a point of coordinates w and y then:

which, when r is very small with reference to x becomes:

replacing in (35):

and making:

as t and sin (t-c) will be negligible with reference to K:

which are the parametric equations of a parabola, previously well known for this particular application and which is, therefore, not claimed as new. It is to be noted that this only happens when the light source becomes a point and that the results (emission of all the light in a single direction forming the angle c with the vertical) may be far from desirable in practical applications.

ln some cases, especially when the fixtures have to be mounted at low height above eye level, it may be desirable to prevent brightness from being seen, not beyond certain angles, but beyond certain eye locations.

For instance, in the case of FIG. 5, it may be desirable that no brightness should be seen from locations to the right of R (at the same level). It will not matter if brightness is seen at points such as Q, at angles larger than c. but smaller than (I. In some cases of low ceilings this ditference may be more than ten degrees. By taking advantage of these extra angles fixtures of even smaller physical size, higher eflflciency, softer beam edges and better appearance may be obtained.

If it is desired that the reflecting surface 2 should reflect the extreme tangents to a point R, of coordinates a, b (FIG. 5), instead of reflecting them at an angle c, the tangent to the desired curve 2 will always be common with the tangent to an ellipse having one fixed focus at R and a second movable focus at x, y, and containing the point X, Y. As the point of tangency keeps moving along curve 1, the ellipse keeps changing continuously. generating the curve 2, which is thus very different from any single ellipse. Because of the well known property of the ellipse, as the focus 1, y moves along the curve 1, the sum (D-l-L-ts) must remain constant, calling it E:

Looking at HO. 5, it is possible to express D as a function of known quantities and of L:

squaring 9A and replacing 10A: ll A) L ls 21'] L 2H5 QLs h ft/ -Ull'lW' As 3A and 4A also hold in this case, replacing 12A in them:

t l +r/ -2w'+ w' where all the symbols have been defined at (2), (4(1), (41)) and elsewhere.

Lighting fixtures made in accordance with the present invention make it impossible to see any direct reflection of any brightness outside of the area within the angle c beneath the unit. Thus the most ideal conditions will be obtained with the fixture occupying the minimum possible volume. In many cases, however, these ideal conditions may not be required.

In general, for instance, there is no practical advantage in the fact that no direct reflections of the room can be seen from viewing positions in the same or neighboring rooms or beyond where people cannot actually stand and see the fixture. Thus as a practical matter the formulas given may desirably be varied. For instance, the formulas given will, in general, make the tangent planes at the extreme lowest limit of the inner surface of the fixture 2 vertical. This may make these surfaces ditlicult to produce. If the angle of this tangent plane with the ver- 1O tical instead of being 0 is e, reflections of the room will be seen only at distances greater than:

(38} d hcot e where h is the vertical distance from eye level to ceiling. in practice I: will never be less than 3 feet, so, if no reflections must be seen from distances smaller than 25 feet, it will sullice to make 0 smaller than about 3. For this purpose the inner surface of the fixture 2 can be stopped at a point above the end, as described, and continued downwards by means of a simple cone.

In many cases the height of the fixture may be limited. and therefore 0 may have to be larger than the value that would give the maximum height and thus larger than necessary. For such a large value of c the width of the fixture may become more, or less, than what may be acceptable for architectural reasons. The inner surface of the fixture 2, in such cases, may have to be stopped short or prolonged further than the equations would show.

For reasons such as these, it will be obvious that many compromises may be needed in actual practice, and the surfaces in many cases although always within the scope of the present invention, as defined in the appended claims, may differ substantially from the ideal ones determined by the strict applications of the equations given.

As was mentioned before, the fixtures made in accordance with the present invention prevent viewing, at angles iarger than c, of any direct reflections from the room being lighted. However, they do not prevent multiple reflections, i.e.. reflections of reflections may be seen and will be seen if the reflecting surface has a high reflection factor at angles approaching the normal.

For this reason. as it was mentioned, these surfaces are preferably formed with specular polished black surfaces having a high reflection factor only at grazing angles and very low reflectance at angles approaching the normal. Then as the reflection factor has to be squared, cubed. etc... with multiple reflections and as the objects reflected are part of the room (having a brightness considerably smaller than the source) this makes these multiple reflections practically invisible.

In some situations. however, these multiple reflections may be acceptable in which case any color finish can he used for the reflecting surface. It is clear that the present invention is not limited to black reflecting surfaces and that any surface which is substantially specular and has a shape related to the shape of the source as described falls within the scope of the present invention as defined in the appended claims.

Having now described the nature of the present invent and the manner in which the same is to be performed, what we claim is:

We claim:

1. A light fixture having a light source of substantial dimensions relative to the dimensions of the fixture with a surface of resolution about its vertical axis positioned therein adapted to substantially limit reflections from the interior of the fixture when the fixture is viewed from an angle greater than c with the vertical axis of the fixture comprising a specular surface of revolution which intersects with planes containing the axis of revolution of the light source and of the specular surface in accordance with the following equations:

11 the source surface with the plane of coordinates; E is a constant; c is the angle of the vertical axis of the fixture beyond which reflections are substantially limited; and X and Y are the coordinates of the points of intersection of the specular surface with the plane of coordinates:

2. A light fixture having a light source of substantial dimensions relative to the dimensions of the fixture with a surface defined by a horizontal cylindrical surface having a constant vertical cross-section curved in such a manner that light will not be reflected beyond planes tangential to the source and forming an angle with the vertical axis comprising a specular polished cylindrical surface defined in relation to the surface of the light source by the following equations:

where:

x and y are the coordinates of the points of intersection of the surface of the light source with the plane of coordinates considered which contains an axis perpendicular to the axis of the cylindrical surface and y is the derivative of y with reference to x, y=f(x) defines the intersection of the source surface with the plane of coordinates; E is a constant; and X and Y are the coordinates of the points of intersection of the specular surface with the plane of coordinates:

3. A light fixture having a light source of substantial dimensions relative to the dimensions of the fixture with a surface of revolution about its vertical axis positioned therein adapted to substantially limit reflections from the interior of the fixture when the fixture is viewed from a horizontal plane located at a distance I) under the adopted origin of coordinates on the axis of symmetry, and from locations separated from said axis by a distance larger than a, comprising a specular surface of revolution which intersects with planes containing the axis of revolution of the light source and the specular surface in accordance with the following equations:

12 where:

x and y are the coordinates of the points of intersection of the surface of the light source with the plane of coordinates considered which contains the axis of revolution and y is the derivative of y with reference to x; y:f(x) defines the intersection of the source surface with the plane of coordinates; E is a constant; and X and Y are the coordinates of the points of intersection of the specular surface with the plane of coordinates:

s L V 1+(ggjil;

4. A light fixture having a light source of substantial dimensions relative to the dimensions of the fixture with a surface defined by a horizontal cylindrical surface having a constant vertical cross-section curved in such a manner that light will not be specularly reflected from the interior of the fixture when the fixture is viewed from a horizontal plane located at a distance b under the adopted origin of coordinates, and from locations separated from the adopted vertical axis of coordinates by a distance larger than (1. comprising a specular cylindrical surface defined in relation to the surface of the light source by the following equations:

where:

x and y are the coordinates of the points of intersection of the surface of the light source with the plane of coordinates considered which contains an axis perpendicular to the axis of the cylindrical surface and y is the derivative of y with reference to x; y=f(x) defines the intersection of the source surface with the plane of coordinates; E is a constant; and X and Y are the coordinates of the points of intersection of the specular surface with the plane of coordinates:

X s-L 1+( (2.:

References Cited in the file of this patent UNITED STATES PATENTS 1,302,924 Hollnagel et al. May 6, 1919

Claims (1)

1. A LIGHT FIXTURE HAVING A LIGHT SOURCE OF SUBSTANTIAL DIMENSIONS RELATIVE TO THE DIMENSIONS OF THE FIXTURE WITH A SURFACE OF RESOLUTION ABOUT ITS VERTICAL AXIS POSTIONED THEREIN ADAPTED TO SUBSTANTIALLY LIMIT REFLECTIONS FROM THE INTEROIR OF THE FIXTURE WHEN THE FIXTURE IS VIEWED FROM AN ANGLE GREATER THAN C WITH THE VERTICAL AXIS OF THE FIXTURE COMPRISING A SPECULAR SURFACE OF REVOLUTION WHICH INTERSECTS WITH PLANES CONTAINING THE AXIS OF REVOLUTION OF THE LIGHT SOURCE AND OF THE SPECULAR SURFACE IN ACCORDANCE WITH THE FOLLOWING EQUATIONS:

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