Household mains light dimmers

[Bigus]

Say you have a cluster of 3 x 50W mains halogen GU10 lights connected to a
standard B&Q dimmer switch. If you turn the dimmer so that the lights are
half-brightness, will the lights consume half the power, ie: about 75W in
total?

Bigus

 

[CWatters]

The simple answer is "overall, no" because there are losses in the dimmer.

I also suspect that a halogen bulb is most efficient when operating at its
max rated voltage. Otherwise you could reduce your electric bill by
installing twice as many lamps and running them at half brightness (or even
four times as many at quarter brightness perhaps )

This web site
http://www.renewingindia.org/eefelec.html

says...
Quote:
However, dimming incandescent lamps reduces their lumen output more than
their wattage. This makes incandescent lamps less efficient as they are
dimmed. End quote..

This is may also be a factor...

http://www.gelighting.com/na/faq/hal_dim.html




"Bigus" <someone@somewhere.com> wrote in message
news:bs9912$16tk@newton.cc.rl.ac.uk...

Say you have a cluster of 3 x 50W mains halogen GU10 lights connected to a
standard B&Q dimmer switch. If you turn the dimmer so that the lights are
half-brightness, will the lights consume half the power, ie: about 75W in
total?

Bigus

 

[Jerry G.]

The accurate answer would be depended on the efficiency of the particular
lamp type. Measuring the actual current draw, and calculating the kw/Hrs
would be the best way to determine this. Incandescent lamps are not linear
in their efficiency. Half the number of lumens will not be an accurate way
to say that the lamp is drawing half the power. The heater resistance of an
incandescent lamp is not linear. At a lower temperature or average voltage
drive, the heater resistance is infact lower, thus it is pulling more
current for its amount of lumens output. Therefore, its current pull at
different voltages will also not be linear.

Using a true AC sinewave voltage drive, or a true DC source, if you decrease
the average drive voltage to a lamp by about 10%, you may increase its life
span by more than that amount. At about a 20% reduction of drive voltage,
the life span of some lamp types are more than doubled. Some manufactures
have published this type of data about their lamps.

As for the low cost thyristor lamp dimmers, these dim by changing the duty
cycle by using a phase shifting technique. This infact is not really a
lowered voltage as such. It gives the effect of a lower voltage. Because the
voltage is phase shifted, it infact is pulse chopped, if you were to look at
this on a scope. With many types of lamps, this infact may reduce the
lifespan of the lamp, because of this effect.

The best dimmer would be to use a variac transformer. It is also a very
expensive way to dim lamps. This would allow the load to have a pure
sinewave at an actual reduced voltage. This type of power reduction will not
reduce the lamp life as like on the low cost thyristor dimmers, and will
allow the filament to work normally, but at a lower voltage.

Many types of compact fluorescents, and quartz lamps cannot be dimmed.
Dimming them will damage them, and can even damage the dimmer. Refer to the
manufacture's label on the box that the lamp comes in, or contact the
manufacture for details.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"Bigus" <someone@somewhere.com> wrote in message
news:bs9912$16tk@newton.cc.rl.ac.uk...
Say you have a cluster of 3 x 50W mains halogen GU10 lights connected to a
standard B&Q dimmer switch. If you turn the dimmer so that the lights are
half-brightness, will the lights consume half the power, ie: about 75W in
total?

Bigus

 

[Richard Crowley]

"Jerry G." wrote ...

As for the low cost thyristor lamp dimmers, these dim
by changing the duty cycle by using a phase shifting
technique. This infact is not really a lowered voltage as
such. It gives the effect of a lower voltage. Because the
voltage is phase shifted, it infact is pulse chopped, if you
were to look at this on a scope. With many types of lamps,
this infact may reduce the lifespan of the lamp, because
of this effect.

Do you have any references on this, or is it just a theory?
The ONLY harmful effect of phase-angle chopping may be
the mechanical shock of the sharp wavefront on SOME
particularly flimsy filaments. If they can take full mains
RMS power, why would they be less capable of handling
a fraction?

The best dimmer would be to use a variac transformer.
It is also a very expensive way to dim lamps. This would
allow the load to have a pure sinewave at an actual reduced
voltage. This type of power reduction will not reduce the
lamp life as like on the low cost thyristor dimmers, and will
allow the filament to work normally, but at a lower voltage.

Incandescent lamp filaments are just big resistors that run
white hot. I've never seen or heard of one with so little
thermal mass that they could possibly follow the waveform.
i.e. the thermal mass averages out the power and "ignores"
the waveform.

The perceived reduction of life for halogen lamps is caused
by reduced temperature breaking the halogen cycle. This
happens regardless of the waveform of the power.

Many types of compact fluorescents, and quartz lamps cannot
be dimmed.

Of course "quartz lamps" can be dimmed. They are incandescent
lamps. But you must run them periodically at full power to recycle
the tungsten via the halogen cycle. This has been discussed many
times here and in related newsgroups.

Now if you mean "quartz lamps" that use step-down
transformers, you may have a situation similar to a fluorescent
ballast...

Fluorescent lamps can also be dimmed, but the process is
made more complex because of the ballast. Special ballasts
are made that allow dimming.

Dimming them will damage them, and can even damage the
dimmer.

"Damage" to halogen lamps is only temporary and easily
reversable. OTOH you CAN actually damage dimmer and/
or ballast (but not likely the lamps themselves) if you try to
dim conventional fluorescent lamps.

 

[Davis Redding]

"Richard Crowley" <rcrowley7@xprt.net> wrote in message
news:vuh2ocq90idl0a@corp.supernews.com...

"Jerry G." wrote ...
As for the low cost thyristor lamp dimmers, these dim
by changing the duty cycle by using a phase shifting
technique. This infact is not really a lowered voltage as
such. It gives the effect of a lower voltage. Because the
voltage is phase shifted, it infact is pulse chopped, if you
were to look at this on a scope. With many types of lamps,
this infact may reduce the lifespan of the lamp, because
of this effect.
Dimming them will damage them, and can even damage the
dimmer.

"Damage" to halogen lamps is only temporary and easily
reversable. OTOH you CAN actually damage dimmer and/
or ballast (but not likely the lamps themselves) if you try to
dim conventional fluorescent lamps.

You can use Triac dimmers, professional stage dimmers all use Triacs, with VERY expensive
halogen lamps on them (typically a PAR 64 lamp runs about $50 Cnd), they get dimmed all
the time, as well as turned on and off rapidly. I guess SCRs chop the wave, and yes, a
phase shift occurs. The lamp also starts to make a lot more noise when on a SCR dimmer.


The other problem is the colour temperature is greatly affected. A halogen can have quite
a high colour temp, and dimming it brings it quite lower. A 200W halogen can be in the
same degree Kelvin as a 500W lamp.