Manually controlable light feedback adjustment device for gas discharge lighting systems

A light sensor and light feedback adjustment device is provided for use with a control unit for selectively controlling the light output of at least one lamp of a ceiling-mounted luminaire to which the unit is connected, based at least in part on the level of ambient light feedback to the unit. The device includes a lens holder, a lens element screw-mounted on the lens holder and including a light gathering lens, and an arrangement for, in use, securing the lens holder in place in a ceiling tile of the ceiling on which the luminaire is mounted. The lens holder includes a tubular mounting portion including a central bore therein in which is disposed a fiberoptic bundle that receives light gathered by the lens. A light feedback adjustment arrangement includes an adjustable set screw mounted for movement in a transverse passage located in the lens holder between the lens element and the fiber optic bundle so as to vary the light coupled to the bundle.

FIELD OF THE INVENTION 
The present invention relates to light control systems which use light 
feedback to control the light output of associated lamps and, more 
particularly, to an improved device or mechanism for adjusting or limiting 
such light feedback. 
BACKGROUND OF THE INVENTION 
Most fluorescent lighting systems have a fixed lumen output, except for 
phosphor degradation effects, i.e., the lumen generating arc is either off 
or on at a fixed level. However, a number of fluorescent lamps control 
techniques have, and are being, developed which permit proportional 
adjustment of the fluorescent lamp arc as a means to establish a more 
desirable level of lumen output. Savings in electrical energy accrue in 
such proportional lighting systems where the arc has been reduced from the 
otherwise "full on" level. Besides the economic implications, the ability 
to reduce lighting and still meet the requirements of different tasks 
improves lighting quality. For example, in order to achieve proper 
contrast and reduce reflections, the background lighting provided in an 
area surrounding a video display terminal (VDT) is generally lower than 
that required for high contrast work tasks like reading. Corridors require 
even lower lighting levels and, in general, to provide for uniform 
lighting in a building is wasteful of energy. Moreover, the ANSI lighting 
guidelines for different tasks and building areas vary over a range of at 
least ten to one, which makes adjustable lighting a highly desirable 
building lighting feature. 
Proportional fluorescent lighting control systems generally use pulse width 
modulation of the fluorescent arc or variable frequency control of the 
arc, and/or some form of AC phase control of the fluorescent lamp arc 
discharge current and other parameters. Often, such systems require the 
adjustment of a control potentiometer to provide a varying reference or 
control signal used to establish the level of lamp lumen output. More 
advanced systems also employ a light sensing means for generating a light 
feedback signal which varies as a function of the surrounding ambient 
light. This light feedback signal, after conversion to a related 
electrical signal, and sometimes after summing with another reference 
signal, is used to proportionally reduce the average lamp arc current, and 
hence the light output from the lamps, when a daylight contribution is 
available. (In an open loop system, the summing operation referred to 
above may not be required.) Such systems are also designed to increase the 
average lamp arc current so as to maintain the ambient lighting level at 
the desired level originally set as the lamp phosphors wear and/or as the 
lamps and/or luminaire reflecting surfaces accumulate dirt. Without such 
an increase in the average arc current, an undesired lowering of the lumen 
output would occur. Presently, this problem is too often solved by the 
wasteful practice of over-lighting when lamps are new in order to ensure 
that there will be sufficient lighting when lamps and luminaires become 
degraded. 
It has been shown that localized control of each luminaire is preferred 
because the contribution from daylight decreases with the distance between 
the luminaire and the window wall and daylight contributions in different 
areas may vary as a function of the azimuth angle of the sun, i.e., 
because of different shading effects produced as the sun moves across the 
horizon. With such localized control of individual luminaires, each 
fixture adjusts so that the sum of the daylight and the luminaire light 
meets the desired level. In contrast, in the case of larger area control 
of a plurality of luminaires, a standardized lumen output for all 
luminaires must be established in the area with the least daylight 
contribution. This results in over-lighting a large majority of the 
controlled area, i.e., that part of the area which receives a greater 
amount of daylight than the particular luminaire used to establish the 
lumen set point and adjustment is precluded for different work tasks or 
for variations in visual acuity between different workers whose work area 
is covered by that group of luminaires. Given that such local control is 
preferred, a simple economical means is necessary to set the lumen output 
in each local area at the recommended lumen level for the tasks to be 
performed in that area. 
Localized control may be accomplished by utilizing a magnetic transformer 
ballast with an electronic controller, i.e., a controller such as 
disclosed in my U.S. Pat. No. 4,352,045, or a variable frequency or pulse 
width modulated electronic ballast or yet other means. In all cases, an 
optical pickup device is necessary to measure the localized light level. 
The light level measurement is converted into a corresponding electrical 
feedback signal. This signal is then used to control the lumen output of 
the luminaire. In this regard, the lumen output is increased if the 
ambient lumen level in the surrounding area decreases, e.g., as the 
daylight wanes. On the other hand, the lumen output is decreased if the 
ambient lumen level in the surrounding area increases, e.g., the amount of 
daylight increases. 
Because the control unit, whether an electronic ballast or other 
controller, is generally mounted in a closed ballast compartment within 
the luminaire, the unit is not easily accessible for adjustment purposes. 
Hence, any light adjustment is best accomplished outside of the ballast 
compartment by maintenance personnel. In previous systems developed by me, 
this adjustment was made by attenuating the sensed light measurement by 
varying the distance from the light pickup lens to the optical-electrical 
transducer which converts the sensed light signal into a corresponding 
electrical signal. In this regard, in 1978 I developed a system employing 
an acrylic plastic lens as the light sensor, a fiber optic bundle and a 
photocell transducer wherein the distance between the lens and the fiber 
optic bundle was varied by manually adjusting the relative position of the 
fiber optic bundle in order to provide the desired set point. A system of 
this general type, i.e., one using a light collector and a fiber optic 
bundle, and one which, in practice, was adjusted as just described, is 
disclosed in my U.S. Pat. No. 4,234,820 (Widmayer). 
A later development of my basic idea is disclosed in U.S. Pat. No. 
4,383,288 (Hess, II et al) which is assigned to Conservolite, Inc., a then 
licensee of the assignee of U.S. Pat. No. 4,234,820 mentioned above. This 
patent discloses varying the output of a light collector device including 
a light sampler or gatherer (including a collecting lens) and a light 
receiver (including a fiber optic bundle) by, as in the prior art system 
referred to above, varying the distance between the light sampler and 
light receiver. This is accomplished in the light collector device of the 
Hess, II patent by mounting the light sampler (lens) with a threaded 
portion which is received in a threaded bore in the receiver so that by 
threading the light sampler into and out of the light receiver, the 
distance between the lens and the fiber optic bundle can be varied. The 
Hess, II patent provides that by threading the sampler further into the 
receiver, the amount of light transmitted to the illumination level 
control system is increased, thereby raising the illumination level in the 
controlled area, and that threading the sampler further out of the 
receiver produces the opposite effect. The light collector is illustrated 
in the patent as being secured to a specially shaped mounting bracket 
which is mounted on a T-bar of a suspended ceiling. 
There are a number of disadvantages associated with the adjustable light 
collector of Hess, II. For example, the device requires either gripping 
the collecting lens directly with the fingers to provide the necessary 
threading in or out of the light sampler, or else requires the use of a 
special tool to perform this task, and it will be appreciated that both of 
these approaches have obvious shortcomings. Further, the mounting 
arrangement is cumbersome and the overall device is relatively complex 
given the purpose to be carried out. 
SUMMARY OF THE INVENTION 
In accordance with the invention, a simple, reliable and economical 
mechanical device is provided for setting or adjusting the lumen output in 
local or large area lighting control systems. Access to the reference 
signal input port is not required and the previously adjustable reference 
input signal is set to a fixed level. As a result, the system, with a 
sufficiently high light feedback signal, will provide the minimum lumen 
output with new lamps, clean luminaire reflecting surfaces and diffuser, 
and no daylight contribution to the ambient lighting. After the 
installation of the device in the ceiling, and with the luminaire 
operating at its minimum lumen output level, the installer can adjust the 
lumen output upward by mechanically restricting the amount of light 
permitted to be transmitted to the optical-electrical transducer. 
In accordance with the invention, the lumen output level is set by 
adjusting a simple set screw or like adjustment element mounted in a light 
sensing lens holder of the device. In particular, to increase the light 
output of the luminaire, the set screw is advanced inwardly to block the 
light passageway so as to reduce the feedback signal amplitude, thereby 
calling for more light. When the light passageway is completely blocked, 
no light feedback will be present and maximum lumen output will be 
present. On the other hand, when the light passageway is unobstructed, 
maximum light feedback will be present and the minimum light output will 
be present. Thus, any lumen output within the minimum-maximum range is 
mechanically established by the set screw and, once established under the 
conditions described above, the feedback signal will increase when 
daylight contributions are added and will decrease when daylight 
contributions are subtracted. Further, the system can be adjusted to 
maintain the set level with lamp phosphor or luminaire reflection 
degradation. Thus, it will be appreciated that the system can be adjusted 
to maintain the desired level of light and when no daylight is present, 
the level of light needs to be changed to accommodate a particular task, 
maintenance personnel can readily readjust the set screw to whatever level 
is desired and that level is thus sustained. 
According to a preferred embodiment of the invention, there is provided, 
for use with a control unit for selectively controlling the light output 
of at least one lamp of a ceiling-mounted luminaire to which the unit is 
connected, based at least in part on the level of ambient light fed back 
to the unit, a light sensor and light feedback adjustment device 
comprising: a lens holder, a lens element mounted on the lens holder and 
including a light gathering lens, and means for, in use, securing the lens 
holder in place in a ceiling tile of the ceiling in or on which the 
luminaire is mounted or on or within the luminaire when no daylight is 
available, the lens holder including a tubular mounting portion including 
a central bore therein and having a free end which, in use, extends 
through the ceiling tile, or on a bracket or brackets on or in the 
luminaire, the device further including a fiber optic bundle disposed in 
said central bore so as to receive light gathered by the lens, and light 
feedback adjustment means for controlling the light received by said fiber 
optic bundle from said lens, said light feedback adjusting means 
comprising an adjustable set screw mounted for movement in a transverse 
passage located in said lens holder between said lens element and said 
fiber optic bundle so as to vary the amount of light coupled to said fiber 
optic bundle and said securing means including a locking member for, in 
use, engaging said free end of said tubular mounting portion to secure 
said lens holder in place. 
Other features and advantages of the invention will be set forth in, or 
apparent from, the detailed description of the preferred embodiments of 
the invention which is found hereinbelow.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, there is shown a first preferred embodiment of the 
adjustable light feedback control device of the invention. The device, 
which is generally denoted 10, is mounted in a through hole or opening H 
in a ceiling tile T, and includes a body portion 12 which acts as a lens 
holder. An integral elongate mounting stem 14 in the form of a hollow 
cylinder or tube, extends through hole H. 
An optical fiber (fiber optic) bundle 16 is received in the bore 14a in 
mounting stem 14 and is connected back to the control system for the lamps 
for the luminaire with which the light control device 10 is associated. 
The free end 16a of fiber optic bundle 16 abuts the end of bore 16a 
adjacent a smaller diameter chamber 18 in lens holder body 12. 
A larger diameter bore 19 in lens holder body 12, which is coaxial with the 
bore 14a and chamber 18, is threaded to receive the correspondingly 
threaded end portion 20a of a plastic lens element or member 20. Lens 
member 20 includes a lens 20b at the opposite end thereof and can take a 
number of different forms and which, in the illustrated embodiment, is 
frustocylindrical in shape and includes a slant face 20c. Lens element 20 
is made from a light transmissive plastic so that light received by lens 
20b is transmitted therethrough. 
An orthogonal or transverse bore 22 in lens holder body 12 extends into 
body 12 beyond chamber 18 and threaded bore 19 so as to communicate with 
both. A suitably threaded set screw 24 is received in transverse, threaded 
bore 22 and is adjustable in position along the length of bore 22, using a 
simple screwdriver, so as to control the range of light transmitted from 
lens element 20 to fiber optic bundle 16. In this regard, the amount of 
light received by fiber optic bundle 16 can be adjusted by varying the 
position of set screw between a maximum light passage position whereby set 
screw 24 is withdrawn out of the path between fiber optic bundle 16 and 
lens element 20, and minimum light passage position which set screw 24 
completely blocks this path and thus no light is received by fiber optic 
bundle 16. 
As illustrated, lens holder body 12 includes teeth indicated at 12a in the 
surface thereof which bite into, and mate with, the underside of tile T to 
more firmly anchor lens holder body 12 in place. A spring-type lock washer 
26 engages the free end of mounting stem portion 14 and locks the overall 
device or unit 10 in place. 
In use, the device 10 is installed, in a very simple manner, by merely 
punching a hole, corresponding to hole H, in tile T, and inserting 
mounting stem portion 14 therethrough. The flat mating upper surface of 
lens holder body 12 containing teeth 12a is pressed against tile T and 
lock washer 26 is used to lock the device 12 in this position. 
Referring to FIG. 3, an alternative embodiment of the invention is shown. 
The embodiment of FIG. 2 is similar to that of FIG. 1 and corresponding 
elements have been given the same reference numerals. The only differences 
between these two embodiments is that, in the embodiment of FIG. 2, a lock 
nut 28 replaces lock washer 26 of FIG. 1 and a set screw 24 is provided 
with a shaped end 24a. Regarding the former, it has been found in practice 
that a locking nut has advantages where the device is to be removed (the 
lock washer can be difficult to disengage). However, it will be 
appreciated that other suitable fasteners or locking elements can also be 
used. 
Regarding the light blocking end 24a of set screw 24, suitable contouring 
or shaping of this end can be used to characterize or control the amount 
of light received by optical fiber 16 as set screw 24 is advanced and 
withdrawn so that a desired light transmission characteristic, as a 
function of set screw position, can be achieved. Different shapes of end 
24a, e.g., pointed, rounded, flat or other shapes, can affect the 
generated light signal. 
Referring to FIG. 3, the device 10 is shown installed in a ceiling tile T 
as described above and connected through fiber optics 16 to a control unit 
CU which is preferably of the type described in my U.S. Pat. Nos. 
5,483,127, issued on Jan. 9, 1996, and 5,519,311, issued on May 21, 1996, 
and which is used to control the lumen output of the fluorescent lamps or 
other gas discharge lamps GDL of a conventional luminaire or lighting unit 
LU mounting in the ceiling formed by tiles T. 
It will be appreciated that the light feedback adjustment provided by set 
screw 24 described above can be used to control the settings of lamps GDL 
so that, for example, the desired light level is provided by the lamps 
when no lighting of the area from additional daylight or other ambient 
light is available. 
In the embodiments described thus far, the light signal collected by lens 
20 is transmitted through a non-(electrically) conducting fiber optic 
bundle 16 to a photocell or other suitable light-to-electrical signal 
transducer (not shown) within control unit CU which is, in turn, 
conductively coupled to the control circuitry within that unit. In an 
alternative embodiment, an additional or replacement light sensor LS (see 
FIG. 3), generally corresponding to that described above, can be directly 
located within the luminaire or lighting unit LU. In other words, light 
sensor LS can be employed in addition to device 10, or substituted for 
that device, e.g., in applications where the luminaire receives no 
daylight and the light sensor LS is used to monitor degradation of lamp 
performance over time. In this embodiment, the photocell or other light 
transducer (not shown in FIG. 3) would be co-located with, i.e., disposed 
closely adjacent to, the lens 20, thereby eliminating the need for the 
fiber optic bundle 16. 
An embodiment of the general nature just described is shown in FIG. 4, 
although in this embodiment, the light feedback control device 10 is 
supported in a ceiling tile, as in the embodiments of FIGS. 1 and 2, 
rather than in the housing of the light unit LU. In this embodiment, a 
photocell 30 is disposed within body portion or lens holder body 12 within 
chamber 18. Photocell 30 is connected by a pair of electrical signal'wires 
32 to the control unit (not shown). It is expected that the electrical 
signal wires 32 will likely have to be located within an armored cable or 
conduit (not shown) or first be connected to a photo-isolator at the input 
to the control circuit. 
It is noted that the embodiment of FIG. 4 can be used with a number of 
commercially available dimming ballasts such as the 277 VAC Mark VII made 
by Advance Transformer ("Advance") and the Series 700 Model D 232. C277, 
made by Electronic Lighting, Inc. ("ELI"). These ballasts each have a pair 
of control wires and provide instructions calling for a variable 
resistance to be connected across an internal voltage source of the 
ballast so that a variation of the resistance will provide dimming of 
lamps connected to the ballast. In the embodiment of FIG. 4, the output 
wires 32 of photocell 30 are connected to the electronic ballast wires 34 
of a dimming ballast 36 so that the light signal sensed by lens 20 
(variation of which causes the resistance of photocell 30 to vary) can be 
used to drive the dimming ballast 36 (which can be an Advance or ELI 
dimming ballast) over the dimming range thereof. 
It will thus be appreciated that by adapting the lens 20, lens holder 12, 
lighting control set screw 24 and the photocell 30 as described above, the 
light output of commercial electronic ballasts such as the Advance and ELI 
ballasts can be set for a given task requirement, user need, or building 
area so long as the light output of the lamps falls within the dimming 
range of the ballast. Thereafter, the gas discharge of the lamps 
automatically increases when depreciation factors cause a light output 
diminishment and decreases in proportion to daylight contributions, if 
any, at the lens collection point. Both the Advance and ELI dimming 
ballasts are generally used with a wall-mounted potentiometer to vary the 
current signal flow within the ballast and/or with light related 
electrical signal derived from a single point control system to usually 
drive a plurality of luminaires wherein the luminaries all have the same 
output and thus have to be set for the worst case lighting level within 
that group of luminaires. 
Although the present invention has been described to specific exemplary 
embodiments thereof, it will be understood by those skilled in the art 
that variations and modifications can be effected in these exemplary 
embodiments without departing from the scope and spirit of the invention.