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Light dimmers vs CFLs

  • Thread starter Jeff Strickland
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J

Jeff Strickland

Jan 1, 1970
0
I have installed dimmer switches throughout my house. I installed them
20-ish years ago for a couple of reasons -- I taught my kids that they don't
need bathroom lights on full blast just to pee, and a light on dimly while
watching TV is better than full bright or off.

Now that CFLs have hit the scene, and they don't like dimmer switches, I am
left to wonder if a light on dim uses less energy. Granted there is less
light, but we use lights on dimly far more than lights on full. I just don't
know if a dmmed light equals lower electricity consumption.

Thanks,
 
J

Jeff Strickland

Jan 1, 1970
0
VWWall said:
Most light dimmers are designed to work with incandescent lamps. These
control the brightness of the lamp by switching "on" during only a portion
of the incoming current sine-wave. This is done with a solid state
switch. Unlike a mechanical switch, this is never completely "on" or
"off", so there is always some power lost in the switch. This is small
compared to the power required to run the lamp at full power, so you do
save energy.

CFLs use a switched power supply to generate the voltage they require, and
this will not work with the usual incandescent light dimmer.

The real hope for the future lies with LEDs, (light emitting diodes),
which have even higher efficiencies than CFL's, have extremely long
lifetimes, and can be dimmed.

Yeah, and LEDs do not have the environmental overhead -- mercury content --
of CFLs..

I heard a guy on talk radio a few weeks ago talking about his LED lights. He
admitted they are costly today, but over time and increasing demand, the
prices should come down. An LED light source should be damn near a
life-of-the-home kind of purchase, meaning it should never fail. This is
exciting stuff in the world of lighting.



 
A

Adrian C

Jan 1, 1970
0
Jeff said:
Yeah, and LEDs do not have the environmental overhead -- mercury content
-- of CFLs..

The media will be feeding the alarming headline "LEDs contain Arsenic"
someday soon...
 
P

Palindrome

Jan 1, 1970
0
Jeff said:
I have installed dimmer switches throughout my house. I installed them
20-ish years ago for a couple of reasons -- I taught my kids that they
don't need bathroom lights on full blast just to pee, and a light on
dimly while watching TV is better than full bright or off.

Now that CFLs have hit the scene, and they don't like dimmer switches, I
am left to wonder if a light on dim uses less energy. Granted there is
less light, but we use lights on dimly far more than lights on full. I
just don't know if a dmmed light equals lower electricity consumption.

Let's start with an undimmed 100W incandescent lamp. It uses 1 unit
every 10 hours.

Now dim it to give the same light output as a 60W incandescent lamp. It
won't be as efficient as a 60W lamp, so it will use 1 unit every 14 hours.

Now replace the dimmed 100W incandescent lamp with a 60W incandescent
lamp on full. It will use 1 unit every 16 hours.

Now replace the 60 W incandescent lamp with a 60 W equivalent CFL. It
will use 1 unit every 90 hours.


So dimming incandescent lamps does save energy. But the savings are tiny
in comparison with fitting the correct wattage CFL.
 
| Jeff Strickland wrote:
|>
|> Yeah, and LEDs do not have the environmental overhead -- mercury content
|> -- of CFLs..
|
| The media will be feeding the alarming headline "LEDs contain Arsenic"
| someday soon...

Yep ... that's sure to happen. Just write a letter to the editor telling
people that due to this arsenic danger they need to be careful and not break
those LED bulbs when replacing them.
 
| Jeff Strickland wrote:
|> I have installed dimmer switches throughout my house. I installed them
|> 20-ish years ago for a couple of reasons -- I taught my kids that they
|> don't need bathroom lights on full blast just to pee, and a light on
|> dimly while watching TV is better than full bright or off.
|>
|> Now that CFLs have hit the scene, and they don't like dimmer switches, I
|> am left to wonder if a light on dim uses less energy. Granted there is
|> less light, but we use lights on dimly far more than lights on full. I
|> just don't know if a dmmed light equals lower electricity consumption.
|>
|
| Let's start with an undimmed 100W incandescent lamp. It uses 1 unit
| every 10 hours.
|
| Now dim it to give the same light output as a 60W incandescent lamp. It
| won't be as efficient as a 60W lamp, so it will use 1 unit every 14 hours.
|
| Now replace the dimmed 100W incandescent lamp with a 60W incandescent
| lamp on full. It will use 1 unit every 16 hours.
|
| Now replace the 60 W incandescent lamp with a 60 W equivalent CFL. It
| will use 1 unit every 90 hours.
|
|
| So dimming incandescent lamps does save energy. But the savings are tiny
| in comparison with fitting the correct wattage CFL.

But does dimming a CFL (when the dimmer and CFL are compatible) save energy?
I hear that dimmed CFLs don't live as long.
 
A

Andrew Gabriel

Jan 1, 1970
0
But does dimming a CFL (when the dimmer and CFL are compatible) save energy?

I can't claim to know all CFL dimming technologies, but I can't
think of one where dimming wouldn't save energy.

You might find that dimmable CFL's are not as efficient in the
first place, in some cases. One type of dimming CFL uses cold
cathode tubes, and those are not as efficient as standard
(thermionic) cathodes tubes, particularly in short length tubes
used in CFLs. Thermionic cathode dimmable CFLs may require extra
circuitry to provide power to heat the cathodes when the tube
current drops, and of course use extra power to do this heating.
I hear that dimmed CFLs don't live as long.

The life of a fluorescent tube depends heavily on the control
gear and on many cases, the number of times the tube is switched
on. For CFLs, the control gear temperature also has a significant
effect on the control gear life -- usually it outlasts the tube,
but at high ambient temperatures, it can fail first.

Simply dimming a standard thermionic cathode tube is likely to
reduce tube life. The reduced current will result in electrodes
cooling, which creates a higher cathode fall voltage, which will
cause electrons and ions to be accelerated to higher energy
levels before impact with the filament, which will sputter off
more of the filament coating, resulting in shorter life.
However, control gear designed for dimming may provide auxilliary
power to the filaments to counteract this. That's easier in the
case of control gear which is fully powered and has some type of
dimming input signal. It's harder for control gear which is
just seeing its own supply being dimmed. So I think the bottom
line is that it's going to depend on the quality of the control
gear.
 
J

James Sweet

Jan 1, 1970
0
Jeff Strickland said:
I have installed dimmer switches throughout my house. I installed them
20-ish years ago for a couple of reasons -- I taught my kids that they
don't need bathroom lights on full blast just to pee, and a light on dimly
while watching TV is better than full bright or off.

Now that CFLs have hit the scene, and they don't like dimmer switches, I
am left to wonder if a light on dim uses less energy. Granted there is
less light, but we use lights on dimly far more than lights on full. I
just don't know if a dmmed light equals lower electricity consumption.

Thanks,


Power consumption does drop as you dim an incandescent, but not nearly as
fast as light output, so the savings are marginal, it does provide a nice
mood though.

You can get dimmable CFLs, they cost more and are harder to find, and they
tend to flicker if used exclusively on a dimmer designed for incandescents.

I use CFLs throughout most of my house, and have halogena bulbs I got on
sale in a few lights that are on dimmers.
 
| Power consumption does drop as you dim an incandescent, but not nearly as
| fast as light output, so the savings are marginal, it does provide a nice
| mood though.

At the lower temperature, much of the "light" shifts into the infra-red.
The total output is the same as the input, but more of it is unusable as
visual light. This is what I dislike of dimmers.
 
A

Adrian C

Jan 1, 1970
0
Yep ... that's sure to happen. Just write a letter to the editor telling
people that due to this arsenic danger they need to be careful and not break
those LED bulbs when replacing them.

I've melted parts of an LED with a soldering iron and am still here and
am feeling dsGF G..... <CARRIER LOST AT 11000KBPS>
 
J

Jeff Strickland

Jan 1, 1970
0
James Sweet said:
Power consumption does drop as you dim an incandescent, but not nearly as
fast as light output, so the savings are marginal, it does provide a nice
mood though.

You can get dimmable CFLs, they cost more and are harder to find, and they
tend to flicker if used exclusively on a dimmer designed for
incandescents.

I use CFLs throughout most of my house, and have halogena bulbs I got on
sale in a few lights that are on dimmers.

Does a halogen use less energy than a regular light bulb?

I know they get very hot, and they make loads of light, but I was not
thinking they would be cheaper to operate. I usppose if a halogen rated ar
50W makes as much or more light than a standard bulb rated at 100W, then
that alone would result in an energy saving ...
 
J

Jeff Strickland

Jan 1, 1970
0
Salmon Egg said:
As you dim incandescent lamps, the conversion efficiency drops very
rapidly. There is the Boltzman stating that emission goes as the fourth
power of the absolute temperature. Moreover, the low proportion of
visible radiation compared to total radiation gets diminished further.
This is a consequence of the black body radiation spectrum with
tempertature.

Bill

What does that mean to mere mortals?

You are waaaay over my head on that one.
 
J

Jeff Strickland

Jan 1, 1970
0
| Power consumption does drop as you dim an incandescent, but not nearly
as
| fast as light output, so the savings are marginal, it does provide a
nice
| mood though.

At the lower temperature, much of the "light" shifts into the infra-red.
The total output is the same as the input, but more of it is unusable as
visual light. This is what I dislike of dimmers.


Does that mean that as a practical matter, the light output decreases faster
than the energy consumption? For example, I reduce 75% of the light but only
25% of the consumption?
 
P

Palindrome

Jan 1, 1970
0
Jeff said:
Does that mean that as a practical matter, the light output decreases
faster than the energy consumption? For example, I reduce 75% of the
light but only 25% of the consumption?
You got it.
 
P

Palindrome

Jan 1, 1970
0
Jeff said:
What does that mean to mere mortals?

You are waaaay over my head on that one.
It means that as you dim a lamp, a higher percentage of the light that
comes out from it isn't visible light. It's still there - but your eyes
can't use it.
 
P

Palindrome

Jan 1, 1970
0
Jeff said:
Does a halogen use less energy than a regular light bulb?

A 50W halogen lamp uses the same amount of electricity as a 50W regular
light bulb.
I know they get very hot, and they make loads of light, but I was not
thinking they would be cheaper to operate. I usppose if a halogen rated
ar 50W makes as much or more light than a standard bulb rated at 100W,
then that alone would result in an energy saving ...
Unfortunately, it doesn't make "as much or more".
 
J

James Sweet

Jan 1, 1970
0
Does a halogen use less energy than a regular light bulb?

I know they get very hot, and they make loads of light, but I was not
thinking they would be cheaper to operate. I usppose if a halogen rated ar
50W makes as much or more light than a standard bulb rated at 100W, then
that alone would result in an energy saving ...


It depends. When you run a filament hotter, as a halogen lamp allows,
efficiency improves. As I recall, the Halogena lamps are about the same in
regards to lumens per watt, but they look nice and last about 3x as long.
I've never actually had one burn out, though the lights I use them in are on
relatively little. They have the halogen capsule inside a glass outer bulb
so they don't get any hotter than a normal lamp. Normally they're a bit
overpriced, but Home Depot had 3-packs for 99 cents a few years ago so I
stocked up.
 
C

charles

Jan 1, 1970
0
Does a halogen use less energy than a regular light bulb?
I know they get very hot, and they make loads of light, but I was not
thinking they would be cheaper to operate. I usppose if a halogen rated
at 50W makes as much or more light than a standard bulb rated at 100W,
then that alone would result in an energy saving ...

From use in our village hall, I consider that a 150w halogen gives as much
light as a 250w tungsten, but this is without using a light meter
 
J

James Sweet

Jan 1, 1970
0
charles said:
From use in our village hall, I consider that a 150w halogen gives as much
light as a 250w tungsten, but this is without using a light meter

That's quite optimistic.

It's possible though that the more compact halogen lamp and superior optics
allows more of the light to be put where you want it, which is as good as
making more light.
 
|
| |> On Mon, 07 Apr 2008 03:38:05 GMT James Sweet <[email protected]>
|> wrote:
|>
|> | Power consumption does drop as you dim an incandescent, but not nearly
|> as
|> | fast as light output, so the savings are marginal, it does provide a
|> nice
|> | mood though.
|>
|> At the lower temperature, much of the "light" shifts into the infra-red.
|> The total output is the same as the input, but more of it is unusable as
|> visual light. This is what I dislike of dimmers.
|>
|
|
| Does that mean that as a practical matter, the light output decreases faster
| than the energy consumption? For example, I reduce 75% of the light but only
| 25% of the consumption?

Yes. I don't know that the exact numbers you gave are even close. The
real formula would be more complex as it needs to account for things like
the temperature of the filament, its resistance change, how much of the
spectrum is usable, etc.

If you only need the light of a 25 watt bulb, a 25 watt bulb is the most
efficient way to do it within the confines of incandescent technology.
You can improve on it slightly by using low-voltage halogen bulbs running
at a higher temperature, at the desired wattage. Other technologies give
much better efficiency at any given light output target point.

As for dimming, LEDs are probably the least wasteful at this, when using
a pulse width modulation. Otherwise, the best way to dim any lighting is
"diversity switching" (which means, turn on only enough lights to meet
the desired illumination level and leave the rest all the way off).
 
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