General assembly for controlling light intensity of a gas discharge lamp

A novel dimming assembly for controlling light intensity of a gas discharge lamp, including: PA1 dimming controller having an input terminal connectable to one pole of an alternating current source and having an output terminal connectable to the line leading to one of the two filament electrodes of the lamp, the dimming controller being adapted to provide an attenuated and conditioned power at its output terminal; PA1 the dimming controller being adapted upon feeding the input terminal with the current, to operate in full power mode for a time period t.sub.1, during which the link between the two terminals is in full conductance bringing about full light intensity of the discharge lamp, and being further adapted after t.sub.1 to enter into a dimming mode, during which the link between the two terminals is in partial conductance bringing about attenuated intensity of the discharge lamp; the said time t.sub.1 is sufficient to facilitate effective dimming in the dimming mode. By another embodiment the dimming controller is adapted upon feeding the input terminal with the current, to gradually switching, for a period t.sub.2, into dimming mode in which the link between the two terminals is in partial conductance bringing about attenuated intensity of the discharge lamp, the time delay t.sub.2 is sufficient for facilitating effective dimming.

FIELD OF THE INVENTION 
The present invention concerns an apparatus for dimming light of gas 
discharge lamps such as fluorescent lamps. 
BACKGROUND OF THE INVENTION 
It is very often desired to utilize a lamp at a less than maximum 
intensity. For this purpose, typically dimmers are installed in the 
circuit supplying the electric power to such lamps. 
Most dimmers operate on a basis of chopping the power, meaning, 
transmitting only through part of the time of the alternating current 
cycle, shutting it off during the rest. The extent of the transmission 
time in each cycle determines the amount of dimming. 
Dimmers typically consist of a user-controlled potentiometer operating in 
conjunction with a triac or an SCR. 
Most available dimmers, particularly such as available in domestic use, are 
capable of dimming a light of lamps such as incandescent type lamps or 
halogen lamps. However, standard dimmers are unsuitable for dimming light 
of gas discharge lamps such as fluorescent lamps, high or low pressure 
mercury or sodium lamps, etc. When attempting to dim such lamps by 
conventional dimmers that are used for example, for incandescent or 
halogen lamps, the light of a gas discharge lamp either flickers or 
extinguishes altogether. 
There is a long felt need for dimmers suitable for use with gas discharge 
lamps particularly in view of the popularity of such types of lamps. As is 
no doubt is known to the artisan, the popularity of such lamps stems to a 
large extent from their very high efficiency, meaning the very high ratio 
of illumination intensity to power consumption. 
Gas discharge lamps have a gas filled space or tube with two spaced 
electrodes (heated or not). When heated, an electrode is a two terminal 
filament. One terminal of each of the two electrodes is connected to a 
pole of the AC power source and the other terminals of the two electrodes 
are typically linked together by the intermediary of a so-called 
"starter". 
A choke/ballast is installed between one of the electrodes and the 
respective pole of the power source and sometimes a capacitor is installed 
in series or parallel to the lamp to correct the power factor (cos-fi) 
and/or limit the current. 
In order to initiate an electric discharge through the gas, an initial high 
voltage, that can supply enough electric charge is required. When the 
power is turned on, an appropriate voltage is to be generated to cause 
such a discharge. 
For a fluorescent lamp, that has heated electrodes, the electric current 
flows at first, through the choke, one filament electrode of the starter 
and the second filament electrode of the lamp. After an initial short 
period of time, the filaments are hot and the starter disconnects, with 
the result of abrupt current change through the choke which, in turn, 
causes a very high voltage across the fluorescent lamp, above the 
threshold required for ignition of the discharge. Following initial 
ignition, the gas discharge lamp continues to emit light while the choke 
limits the current, as long as it is supplied with electric power above a 
minimal value. 
There are available dimmers for gas discharge lamps such as fluorescent 
lamps. For example, in Hi-Fi dimmers, the standard choke is replaced by an 
electronic choke which is an oscillator that generates an alternating 
electric power at high frequency, of the order of 25-100 KHz. In such 
dimmers, dimming is achieved by modulating the oscillator and whilst 
effective dimming is achieved, such dimmers entail significant drawbacks 
in that they are somewhat inefficient and expensive and that retrofitting 
a light circuit to operate them requires relatively expensive hardware. 
Other types of dimmers involve the use of a heating transformer intended to 
preheat the filaments in order to reduce the threshold voltage required to 
initiate the gas discharge. 
The drawback here is similar to that of the Hi-Fi dimmers in that it 
requires a very expensive hardware. Furthermore, such dimmers are 
inappropriate for various kinds of gas discharge lamps that do not depend 
on preheating of their electrodes such as various types of high pressure 
gas discharge lamps and high or low pressure mercury or sodium lamps and 
others. 
It is the object of the present invention to provide a novel dimmer for gas 
discharge lamps. 
It is furthermore the object of the invention to provide a dimmer which can 
easily be installed in already existing installation of gas discharge 
lamps. 
It is furthermore the object of the present invention to provide such 
dimmers involving the use of inexpensive hardware. 
GENERAL DESCRIPTION OF THE INVENTION 
The present invention is based on the surprising finding that unlike prior 
belief in this field, effective dimming of a gas discharge lamp may be 
achieved by the use of circuitry, which can be installed into a standard 
circuitry without a need for cumbersome and expensive retrofitting of the 
circuitry. 
The term "effective dimming" used above and below, denotes the dimming of 
light for prolonged time periods without light flicker or occasional lamp 
extinguishing. 
It has been found in accordance with one embodiment of the invention, that 
where a relatively high degree of dimming is desired, to achieve light 
output less than 50% of maximal output, the lamp has to operate at 
essentially maximum power for a certain period of time before effective 
dimming can be achieved. The extent of time in which the lamp has to 
operate in full power depends on the extent of dimming desired. It should 
nevertheless be appreciated that the term "full power mode" is to be 
interpreted in the context of the description and the appended claims as 
essentially "full power mode". Thus, for example, 90% of the maximal power 
is considered in some cases as full power mode. 
Thus, in accordance with the present invention there is provided a dimmer 
assembly for controlling light intensity of a gas discharge lamps, 
comprising: 
dimming controller having an input terminal connectable to one pole of an 
alternating current source and having an output terminal connectable to 
the line leading to one of the two filament electrodes of the lamp, the 
dimming controller being adapted to provide an attenuated and conditioned 
power at its output terminal; 
the improvement being in that: 
the dimming controller being adapted upon feeding the input terminal with 
the current, to operate in a first mode constituting a full power mode for 
a time period t.sub.1, during which the link between the two terminals is 
in full conductance bringing about full light intensity of the discharge 
lamp, and being further adapted after t.sub.1 to enter into a second mode 
constituting a dimming mode, during which the link between the two 
terminals is in partial conductance bringing about attenuated intensity of 
the discharge lamp; the said time period t.sub.1 is sufficient to 
facilitate effective dimming in the dimming mode. 
In accordance with a second embodiment of the invention it has been found 
that particularly where the dimming means controls light in a plurality of 
lamps, in order to achieve effective dimming, the transition from a 
non-dimmed, i.e. maximal power state, into a state in which the light has 
been dimmed should be gradual. The duration of the transition period 
between maximal power state and a dimmed state depends on various factors 
including the number of lamps, the type of lamps used and other factors. 
The correlation between these factors and the aforesaid time duration has 
to be determined in each particular case. 
Accordingly, by a second aspect of the invention there is provided a dimmer 
assembly for controlling light intensity of a gas discharge lamp, 
comprising: 
dimming controller having an input terminal connectable to one pole of an 
alternating current source and having an output terminal connectable to 
the line leading to one of the two filament electrodes of the lamp, the 
dimming controller being adapted to provide an attenuated power at its 
output terminal; 
the improvement being in that: the dimming controller is adapted upon 
feeding the input terminal with alternating electricity, to gradually 
switch, for a transition time period t.sub.2, into dimming mode in which 
the link between the two terminals is in partial conductance bringing 
about attenuated intensity of the discharge lamp. The said transition time 
period t.sub.2 is sufficient for facilitation of an effecting dimming in 
the dimming mode. It may be appreciated by the artisan that in various 
applications a dimming assembly may incorporate characterizing features of 
both of the above embodiments. Thus, by way of example, in case of a large 
number of lamps and a high degree of desired dimming, both a full power 
and a gradual transition to dimming mode may be implemented. 
It should be noted that the time periods t.sub.1 and t.sub.2 should be 
adjusted in accordance with the particular application. Typically, the 
extent of the desired dimming, the number and type of lamps used and 
various other factors affect the values of t.sub.1 and t.sub.2. By way of 
example, in case of a single lamp and a desired dimming extent of 50%, 
t.sub.1 may be selected to be 50 secs. and t.sub.2 to be 200 secs. It 
should be noted that for a given lighting system t.sub.1 and t.sub.2 may 
be automatically adjusted for a given desired dimming extent. 
The dimming controller in the dimmer assembly of the invention may be any 
suitable means such as those operated on the basis of signal chopping, 
e.g., using triacs or SCRs, using an impedance control system, etc. 
In case of signal chopping, the dimming is achieved by blocking the 
electric current from going through the lamps during part of each half of 
the AC cycle, following the "zero crossing", and letting it flow during 
the rest of the half cycle. This chopping repeats itself each half cycle. 
Typically, a triac or twin SCR's together with a programmable controller 
and timer, form collectively the dimming controller of the invention. In 
case of high dimming extent, and the consequent risk of damage by virtue 
of power spikes, the triac, if needed, is protected by a passive "body 
guard". 
The Triac body guard is typically a saturable inductor or a collapsible 
resistor that restricts the current during switching of the signal 
chopping means but has essentially no impedance once the current exceeds 
some critical value. By so doing, the body guard greatly diminishes the 
energy deposition in the signal chopping means during the switching time, 
thereby protecting it from being damaged. 
In case of a power failure, when the power is resumed, the controller 
repeats the foregoing sequence of operations whereby the lamps are 
automatically restarted and brought into the desired dimmed condition. 
It has been found that effective dimming of fluorescent lamp or lamps 
assembly, to an extent in which the lamp's illumination intensity drops 
below about 80% of its maximum, can be achieved by replacing the standard 
starter coupling between the filaments, which is typically a bimetal based 
device, with a staffer which during the ignition process and after an 
initial time delay in which current passes there-through, essentially 
disconnects the electric contact between the two filament electrodes of 
the lamp, whereby the only electric path between the two electrodes being 
then through the discharge gas inside the lamp. An example of such a 
starter is an electronic starter, many of which are available. 
Thus, in accordance with another embodiment of the present invention, there 
is provided a dimmer assembly of the kind specified further comprising a 
starter unit having two terminals one connectable to each of the filament 
electrodes of the lamp, which, when initially energized enables electrical 
connectivity between the electrodes, and after a predetermined time delay 
disconnects the said electrical connectivity, whereby the only connection 
between the two electrodes being then through the discharged gas inside 
the lamp. By disconnecting, it is meant that the current flow through the 
starter drops to essentially zero. 
The starter in accordance with this embodiment, may be, by way of example, 
an electronic starter. It should be noted that contrary to such an 
electronic starter, the standard bimetal starters can resume contact if 
the voltage decreases beyond a certain value and thus by the use of such 
starters, in a dimming mode of operation, there is risk of light 
flickering or a total distinguishing thereof. 
The present invention further provides a lighting system comprising: 
one or more gas discharge lamps each having two spaced electrodes, each 
electrode connected to one pole of an electric power source; 
choke means and a starter unit associated with each lamp, and a dimmer 
controller on the electric line connecting one of the electrodes of each 
lamp to the one terminal of the power source, the dimmer controller being 
one of those specified above. 
Retrofitting existing lighting systems to a system in accordance with the 
invention is a very simple and rapid procedure and involves only changing 
of the standard light switch to a dimmer assembly of the invention and 
setting the potentiometers and possibly, for fluorescent lamps that have 
filament-electrodes and use a bimetallic starter, also replacing the 
starter of each lamp with an electronic starter. There is no need for any 
additional change in the circuitry, unlike most other dimming systems 
available to date. 
The operation in the dimming mode is characterized by an increase in the 
efficiency, that is the "light to power" ratio. It has been found that 
dimming in accordance with the invention is efficient in terms of 
consumption of energy. 
The invention will be illustrated in the following by a description of some 
specific, currently preferred non-limiting embodiments.

DETAILED DESCRIPTION OF THE INVENTION 
The controller of the present invention can be realized by utilizing 
digital components, analog components or a combination thereof. 
By one embodiment the controller consists exclusively of hardware 
components. The time period t.sub.1 of the full power is determined by an 
RC circuit and its setting is made with a potentiometer. The transition 
time period t.sub.2 is controlled by another RC circuit and is set by a 
second potentiometer. The level of dimming is set by a third 
potentiometer. Alternatively, the operation of the dimming controller may 
be realized by a suitably programmed controller. 
For the explanation of a second far more detailed embodiment, attention is 
first directed to FIG. 1 showing a light system of the invention. The 
system of this embodiment includes a plurality (n) identical fluorescent 
tubes of which only two are shown, those designated F1 and Fn. These 
fluorescent tubes may for example be standard, 40 W "day light" type of 
the kind manufactured by OSRAM.TM.. Each of the tubes includes two spaced 
electrode filaments 5 and 6. One terminal 7 of filament 5 is electrically 
coupled to a proximal terminal of choke ballast 8, being for example of 
the kind manufactured by SHWABBE. Terminal 9 of electrode filament 6 is 
connected to one terminal of an AC (alternating current) power source, 
e.g. 220 volts, 50 Hz. The other terminals 11 and 12 of electrode 
filaments 5 and 6, respectively, are electrically coupled to respective 
terminals 13 and 14 of starter 15. 
Dimmer assembly 17 comprises an on/off switch 18 (which may be coupled to a 
potentiometer 25 but which is shown herein for the sake of clarity as a 
separate component), dimming controller 19 and a bypass means 20. 
Dimming controller 19 has an input terminal 21 and an output terminal 22. 
Linking the two terminals 21 and 22 is a triac component 23 which should 
be selected so that its maximal power output is compatible with the power 
requirements of the plurality of fluorescent tubes F1 to Fn. The power 
transmission through triac 23 is controlled by gate 24. Potentiometer 25 
(which as pointed out above is coupled to switch 18) is linked to a user 
controlled dial whereby the user selects the required dimming degree. 
Potentiometer 25 operates in a combination with capacitor 26, resistor 27 
and diac 28, in a manner which is no doubt clear to the artisan to 
modulate the voltage at gate 24 whereby the electric power through triac 
23 is chopped depending on the selected position of potentiometer 25. (It 
should be noted that bypass means 20 may be implemented by triac 23 which 
when set to full conductance, by suitable modulation of gate 24, 
facilitates the bypass mode and alternatively when set to partial 
conductance facilitates the dimmed mode. 
The dimming means also comprises an optional histeresis compensating 
circuitry generally indicated 30 which comprises four diodes 31-34 and 
resistors 35 and 36. The function of the histeresis compensation unit is 
to render the dimmer operation symmetrical in the sense that the current 
attenuation upon increase in the degree of attenuation will be the same at 
each point as where the dimming degree is decreased. The histeresis 
compensating means essentially confers increased users' convenience in 
that it neutralizes the known histeresis effect which is a common drawback 
shared by many dimming units. 
As shown in FIG. 1, the dimmer assembly 17 comprises also a gradual dimming 
controller 40, adapted to provide for a gradual entry into a dimmed mode, 
and compensator resistor circuitry 50 the function of which will be 
elaborated further below. 
In operation, when switch 18 is closed, bypass means 20 short circuits 
terminals 21 and 22 and consequently the entire electric power flows 
directly at full intensity to the plurality of fluorescent light bulbs F1 
to Fn through their associated chokes 8. After a certain time delay, its 
minimum depending on the selected dimming extent determined by the 
position of potentiometer 25, the bypass means switches from the full 
power mode, to the dimming mode in which the direct connection between 
terminals 21 and 22 is disconnected and consequently the power between 
these two terminals is now routed entirely through dimming controller 19. 
The extent of power output at terminal 22 is determined by means of 
potentiometer 25 as explained above. 
As can also be seen in FIG. 1, the system can operate with a plurality of 
fluorescent lamps, unlike many dimmers that are available today. However, 
when plurality of fluorescent lamps are utilized the gradual dimming 
controller 40 should be activated. 
Saturable indicator 55 and its associated control circuitry shown 
schematically as component 56 being the "body guard" which, as recalled, 
serves for protecting the triac 23 from being damaged. 
Reference is now being made to FIG. 2, showing a circuitry of the 
electronic starter unit 15 in FIG. 1. Starter 15 consists of an SCR 60 
linked to terminal 11 through the intermediary of diode 61 and to terminal 
12 through the intermediary of diodes 62-65. The circuitry further 
comprises an SCR 67, additional diodes 71-73, zener diode 74, a plurality 
of resistors 77-82 and three capacitors 83, 84 and 85. In operation, the 
sub-circuit consisting of resistors 77, 78, capacitors 83 and 84, diode 
71, and zener diode 74 which is linked to gate 90 SCR 60, brings SCR 60 
into a conduction mode in which current flows between terminals 11 and 12. 
After a certain time delay depending on the time constant of the 
sub-circuit consisting of resistors 79, 80, 81 and capacitor 85, SCR 67 
enters into conduction mode whereby SCR 60 is disconnected and 
consequently the electrical contact between terminals 11 and 12 is 
disconnected. This disconnection then facilitates the ignition of the gas 
discharge effect as already discussed above. 
As long as potential is applied to terminal 11, conductive conditions are 
maintained in SCR 67 and consequently SCR 60 is constantly disconnected 
essentially independent of the voltage at terminal 11. 
Attention is now being made to FIG. 3 showing a system in accordance with 
another embodiment of the invention. The operation of dimming assembly 101 
in accordance with this embodiment is essentially similar to that in the 
embodiment of FIG. 1, the two differing from one another by the dimmer 
controller, generally designated 102, which in the embodiment of FIG. 4 
operates on the basis of impedance control. All other features of the 
system are essentially identical to those of FIG. 1 and were given the 
same reference numerals with prime indications. 
Dimmer means 102 comprise a primary coil 105 and a secondary coil 106. The 
dimming effect is achieved by changing the induction ratio between the 
primary and secondary coils 105, 106, respectively, which, in practice is 
obtained by selecting the active taps of coil 106. The taps are associated 
to user controllable dimming control means 107, whereby the user is 
capable of selecting the desired dimming extent. The number of taps 
determines the number of dimming levels. In FIG. 3, three taps are shown 
although it will be appreciated by the artisan that this is only an 
example and the secondary coil may have any other number of taps. 
Auxiliary unit 108 has the same function as auxiliary unit 40 in FIG. 1. 
Attention is now directed to FIG. 4 showing the circuitry of the bypass and 
the gradual dimming means (components 20 and 40). It should be noted, 
however, that in FIG. 4 both bypass means 20 and gradual dimming means 40 
are incorporated together into one circuitry. 
Potentiometer 200, 201, amplifiers 202, 203, diodes 207, 220, resistors 
210, 213 and capacitor 215 constitute collectively the bypass means. The 
incorporation of the circuitry shown in FIG. 4 within the dimmer 
controller, such as that shown in FIG. 1, is not shown in the drawings as 
being straightforward to those versed in the art. 
In operation, potentiometer 200 (which is similar in its function to 
potentiometer 25 of FIG. 1) is set to the desired dimming extent which 
should exceed a minimal threshold defined by reference voltage fed to the 
negative input of amplifier 202. The setting of potentiometer 200 results 
in generation of saturation voltage at the output of amplifier 202. The 
latter imposes a reference voltage, e.g. about 7.5 V, at the positive 
input of amplifier 203 which in turn forces positive saturation at the 
output of amplifier 203 thereby facilitating the so-called full power 
mode. The negative input of amplifier 203 will exceed the 7.5 V reference 
voltage after the capacitor 215 is charged to the suitable threshold so as 
to force an equivalent voltage (e.g. about 7.5 V) at the negative input of 
amplifier 203. 
The charging rate of the capacitor 215 is contingent on the time delay 
defined by the potentiometer 201 and capacitor 215, and may, for example, 
be about 3 minutes. Once the negative input voltage of amplifter 203 
exceeds the reference voltage, the output of latter drops to 0 due to 
diode 207. 
As the power at the output of amplifier 203 drops to 0, the input power is 
routed via triac 23 (refer to FIG. 1) thus facilitating the so-called 
dimmed mode. The control signal to the gate of the triac 23 is fed via the 
potentiometer 200 and diode 220. It should be noted that the circuit may 
be easily modified, as is well known to the artisan, so that the position 
selected by the user in potentiometer 200 controls the time delay which in 
FIG. 4 is determined merely by the combination of potentiometer 201 and 
capacitor 215. 
The gradual dimming is achieved by potentiometers 200, 222, diodes 207, 
220, amplifier 203 and capacitor 221. As the power of the output of the 
diode 207 drops to zero (which is due to the negative saturation at the 
output amplifier 203), the voltage potential of junction 223 remains in 
positive saturation due to capacitor 221 which was changed during the full 
power mode period thus maintaining initial full power in spite of the 
power drop at the output of amplifier 203. The gradual attenuation 
terminates as the voltage potential at junction 223 drops to the level 
determined by the potentiometer 200 (via diode 220) entering full dimmed 
mode. 
It should be noted that by this embodiment there is no discrete path which 
bypasses triac 23. Accordingly, the current flows through the triac both 
in full power mode and in dimmed mode. However, in the latter mode the 
gate controls the operation of the triac whereas in the prior, the gate 
provides a constant power supply thus facilitating the full power mode. 
It should be noted that in lighting system in which an anti-cosinus .phi. 
capacitor is installed, an impedance control dimmer assembly similar as in 
the embodiment in FIG. 3 was found to be advantageous over use of the 
wave-chopping based system as in the embodiment of FIG. 1. The system of 
the invention is applicable for a large number of gas discharge lamps. 
Hitherto available dimmer systems have failed to work with various types 
of fluorescent lamps which are effectively dimmed by the use of the dimmer 
assembly of the invention. For example, the assembly of the present 
invention works very effectively for dimming light of a fluorescent lamp 
of the kind having a 26 mm diameter, 36 W power employing a so-called 
rapid start starter. Obviously, the assembly is also applicable for 
various other lamp types such as, for example, 18 W or 58 W lamps of the 
same diameter. 
In some cases, it is necessary to utilize compensating resistors. 
Compensating resistors 50 in FIG. 1 and 50' in FIG. 3 are connected in 
parallel to bypass means 20 and 20', respectively and a compensating 
resistor 51 is connected between the output terminal 22 line 52. For 
example, a 5 W, 1 k.OMEGA. or 2.5 k.OMEGA. compensating resistor is 
applicable in the case of the abovementioned fluorescent lamp. The 
determination whether to employ single or both of the compensating 
resistors and their values is made empirically in each case. It should be 
noted that the use of such compensating resistor may be utilized also in 
systems in which gradual dimming controller or bypass means are not 
required. 
The system of the invention is also applicable for dimming light of various 
compact fluorescent lamps, having integral built-in starters such as those 
manufactured by OSRAM.TM. or PHILLIPS.TM.. In this connection it should be 
noted that for fluorescent lamps utilizing power up to 20 W, a bimetal 
starter may be utilized, but this has to be replaced with an electronic 
starter similar to that shown in FIG. 3, where the fluorescent lamps are 
of a higher power type. 
It should be noted that by another embodiment, an additional circuitry may 
be incorporated to the assembly of the invention, which, in case of an 
instantaneous power loss delays the resumption of power to the system for 
a certain time interval, e.g. for 30 secs. 
It has further been found that in cases of unstable power supply, in which 
the input power changes unpredictably, it is advantageous to employ a 
power control unit which will provide the circuitry of the assembly with 
stabilized input power regardless of any interference in the actual power 
supply. 
It shall no doubt be appreciated by the artisan that the specifically 
described embodiments are an example only of a much larger scope of the 
invention as defined herein. Thus, by way of example, the dimmer assembly 
of the invention may be used in light system employing sodium or mercury 
lamps. Furthermore, in the drawings specific values of resistors, 
capacitors, and diodes are given, it will no doubt be appreciated that 
various others may be used in the circuits shown in the figures, and also 
there are various alternative circuitry designs to obtain equivalent 
function.