Electric lamp and discharge devices: systems – Current and/or voltage regulation – Automatic regulation
Reexamination Certificate
2000-06-16
2001-10-09
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
Automatic regulation
C315S224000, C315S158000, C315S159000, C250S2140AL, C250S2140LS
Reexamination Certificate
active
06300728
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to fluorescent lighting systems, and more particularly to a fluorescent lighting system adapted for quickly achieving full illumination in cold environments.
2. Description of the Prior Art
In many lighting applications, fluorescent lighting is needed to achieve the proper background illumination. Fluorescent lighting traditionally has provided high illumination at low cost and low power consumption. In contrast with an incandescent light which produces light by heating of a filament, a fluorescent light produces light by exciting atoms of a gas.
An example of a common tube-shaped fluorescent light is depicted at
FIG. 1. A
fluorescent bulb
10
includes a tubular glass shell
12
which is internally coated with a phosphor
14
, such as for example calcium tungstate. Within the glass shell, the air is pumped out and replaced with an inert gas, usually argon. Added to the noble gas is a small amount of mercury. Two mutually spaced apart electrodes
16
,
18
are located at either end of the shell. In operation, power is applied to the circuit (120 VAC), and a starter switch
20
is momentarily closed. About a second later, the starter switch opens, whereupon a choke or ballast
22
provides a voltage pulse which causes the gas within the shell to become excited and thereby emit light as electrons strike the gas molecules. The emitted light is mostly in the invisible ultraviolet portion of the spectrum. However, when this emitted light strikes the phosphor
14
, the phosphor fluoresces, providing copious amounts of visible light.
A fluorescent light requires a unique power supply that heats the electrode only temporarily to achieve electron excitation of the mercury vapor. The ballast balances the inrush current in combination with a high voltage required for gas excitation. These power supplies require careful attention to design, and add an additional cost above that which would be required to power an incandescent light bulb. In addition, fluorescent lighting is notoriously slow to illuminate at cold temperatures, for example less than about zero degrees C. Still another limitation for the application of fluorescent lighting is the relatively long bulbs that are required. These bulbs have to be packaged with maximum mechanical damping to survive even modest vibrations.
One advance of conventional tube-type fluorescent lighting systems provides quick starting. According to one form of improvement, known as “preheat”, the cathode electrodes are preheated when first turned on. When the starter switch opens, the current arcs through the tube, keeping the cathode electrodes hot. According to another form of improvement, known as “instant-start”, there is no starter switch and the cathode electrodes are short circuited. A high voltage (for example 500 volts) is applied at the start of the fluorescent light. The high voltage induces illumination, and the ballast returns the voltage to operating levels. According to yet another form of improvement, known as “rapid-start”, there is no starter switch, but the cathode electrodes are not short circuited. Special windings in the ballast provide preheat of the cathode windings, and the fluorescent light is started by a high voltage as in the instant-start modality.
A new type of fluorescent lighting system on the market is “sub-miniature fluorescent light” (SFL), an example of which is available from Stanley Electric Co., Ltd. of Tokyo, Japan, and is currently being sold as model T4.7SSL. The Stanley SFL
50
, shown at
FIGS. 2A and 2B
is a low power, low voltage type, having a convexly configured glass shell
52
coated interiorly by a phosphor
56
, and filled by an inert gas with a little mercury
54
. Electrically, situated within the shell are a cathode
58
having a resistive cathode element
60
, an anode
62
spaced from the cathode, and three terminal leads: a ground
64
terminal lead, an anode terminal lead
66
, and a cathode terminal lead
68
. The Stanley SFL
10
is packaged in a size analogous to small automotive incandescent lights of the type used for automotive interior lights. This small packaging allows for a small bias voltage Va at the anode, typically 24 volts. The cathode element is approximately 26 ohms to the ground terminal lead, requiring a cathode voltage Vc of only 5 volts to provide enough excitation power to warm the ionized gas inside the shell. When the gas warms it is able to conduct anode current to ground through the ionized gas, and light is emitted as electrons strike the mercury atoms. The emitted light is mostly in the invisible ultraviolet UV portion of the spectrum. However, when this emitted light strikes the phosphor
56
, the phosphor fluoresces, providing copious amounts of visible light V.
While an SFL is technically improved over conventional fluorescent lights, it still has some drawbacks. For example, if the ambient temperature is cold the cathode warming of the gas is insufficient to conduct the required anode current. This results in a fluorescent light that does not illuminate well at cold temperatures and/or a fluorescent light that takes minutes to warm enough to produce the required illumination. Still another limitation is that the expected life of an SFL is relatively short, for example around 5000 hours. This illumination life is based on an expected decrease of illumination with use, wherein life is considered to have ended when an aged SFL has an illumination output that is one half of that when it was new.
Accordingly, while an SFL overcomes the fluorescent light problems of fragility and power supply complexity, it remains a problem in the art to overcome the disadvantages associated with poor cold starting and short life expectancy.
SUMMARY OF THE INVENTION
The present invention is a power supply for a fluorescent light, particularly a sub-miniature fluorescent light (SFL) which provides compensation for temperature and age effects of the fluorescent light.
One or more SFLs are powered by a variable output anode controller and a variable output cathode controller, wherein the illumination output of the SFLs is selectively adjustable based upon the voltage output of one or both of the anode and cathode controllers.
In a first example of implementation of the invention, an illumination feedback circuit is provided to the anode/cathode controller, wherein the voltage output is adjusted to compensate for diminished illumination, caused for example by cold operating conditions or age of the sensed SFLs. For example, the illumination feedback is provided by a light sensor adjacent one or more of the SFLs which detects the illumination being output by at least one of the SFLs.
In a second form of the present invention, a temperature feedback circuit is provided to the anode/cathode controller to provide the aforesaid voltage adjustment to compensate for diminished illumination. For example, a thermistor adjacent the SFLs provides a temperature signal which is used by a control program to provide adjustment of the anode and/or cathode controller output based upon a predetermined temperature to illumination output relationship.
In another aspect of the present invention, the SFLs are placed into a ready-state for being presently illuminated based upon sensing of a wake-up signal. For example, when a user performs an act, as for example the opening of a car door, a wake-up routine is initiated which adjusts the anode and/or cathode controllers so as to ready the SFLs for illumination in a predetermined present length of time. An example for carrying-out this feature of the invention is to use any of the aforesaid feedback modalities in combination with a predetermined wait-state illumination output from at least one of the SFLs.
Accordingly, it is an object of the present invention to adjust illumination output of fluorescent lighting compensatorily for effects of temperature and age.
It is a further object of the present invention to provide a power supply for a fluorescent lights which includes an
Blackburn Brian K.
Gentry Scott B.
Mazur Joseph F.
BGM Engineering, Inc.
Keefe Peter D.
Philogene Haissa
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