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#55689 09/03/05 12:00 AM
Joined: Dec 2003
Posts: 524
... Maybe this has been covered already,but,I was engaged in a heated debate today at the counter of my supply house...The topic... "Does it save money by using a dimmer or not",.. I say no,..that whatever is consumed,ie;60 watt light bulb, still 60 watts consumed, dimmer or no dimmer, because the light output may be less,but the energy is dissipated in HEAT,..therefore,the meter sees the same consumption. Come on guys let me know if my head's been baking up in the attic too long,or am I correct in my assumption..

.."if it ain't fixed,don't break a Licensed Electrician"
#55690 09/03/05 12:09 AM
Joined: Jan 2004
Posts: 615
yeah, I hear the same rhetoric from the dimmer guys too. I cornered one once and finally got him to admit that you saved money, but you were getting less light and paying more for it than if you were running a lower wattage bulb. I'm no authority but logic and my understanding of the workings of the universe tells me that you get what you pay for. You pay for light and you pay for heat. A 60 watt bulb dimmed to 50% will cost 40% less than no dimmer. But a 30 watt bulb will cost 50% less. I think it is very misleading the way these dimmer companies market this way.

#55691 09/03/05 12:40 AM
Joined: Jul 2004
Posts: 9,931
Likes: 34
The first thing you have to understand about a dimmer is that it is a switch that goes on and off really fast, so you are saving power when it is off (during part of the cycle).
The only argument is how much you save vs the light you get. There is also the factor of bulb life.
Most people use dimmers because they want to be able to dim the light. Saving energy is a secondary but real advantage when they are dimmed.
I also use a dimmer on luminaires that have expensive bulbs which don't normally last too long.

Greg Fretwell
#55692 09/03/05 02:14 AM
Joined: Oct 2004
Posts: 806
I say no,..that whatever is consumed,ie;60 watt light bulb, still 60 watts consumed, dimmer or no dimmer, because the light output may be less,but the energy is dissipated in HEAT,..therefore,the meter sees the same consumption.

With the old-style resistance (and even some old reactance) dimmers, yes, you're right. The power otherwise used to heat the filament is lost as heat.

With the newer solid-state triac/SCR dimmers, not really. Although some losses occur in the electronics, they do function as gfretwell said by interrupting the current flow many times a second, so the meter would not read the same consumption. Less energy is indeed used.

So depending on what kind of dimmer you're talking about you're both right and wrong. [Linked Image]

BTW, I've enjoyed reading your posts and seeing the photos of things you've found!

Stupid should be painful.
#55693 09/03/05 06:36 AM
Joined: Jan 2003
Posts: 4,391
As long as we are talking about new dimmers it does save money.

Look at it this way, in order to consume electricity work must be produced. That work may be heat, light, motion etc.

With a new dimmer less light and less heat is being produced this means less electricity is being consumed.

The old dimmers as has been mentioned 'made' heat to reduce the voltage reaching the lamp, therefore the savings was either non existent or small. I am not sure exactly. [Linked Image]

Personally I have two 250 PAR 38 floods at my back door, I have these rigged on a dimmer and they run very low every night. I don't notice them on my bill which I am sure I would if I ran them full all the time.

Bob Badger
Construction & Maintenance Electrician
#55694 09/03/05 08:45 AM
Joined: Dec 2003
Posts: 524
... Well thanx guys,I guess that clears that's been an age old question that kept popping up..even my mother-in-law was asking about it recently..she's on an energy saving kick,and bought a basketful of those fluorescent screw-in bulbs at Big Orange that supposedly @ 13 watts,"gives the output lumens of a 60 watt incandescent bulb"..that may be so,..but they are ugly as heck to look at,and she's been putting them everywhere,from table lamps to wall sconces...YUCCCK!! and you can't dim them,..
Oh well,it's her house..

...Mxslick,thank you,it's always a pleasure!! [Linked Image] [Linked Image] [Linked Image] [Linked Image]

.."if it ain't fixed,don't break a Licensed Electrician"
#55695 09/03/05 09:47 AM
Joined: Sep 2003
Posts: 650
If you look for them, there are dimmable compact florescent lamps available. These at least hold much of their efficiency when dimmed.

Incandescent lamps are interesting beasties. They are resistance heaters, but the resistance changes by a factor of 10 or so between a cold filament and a hot filament. A 100W lamp will draw on the order of 10A (1200W) at startup.

There are a couple of approximate equations that describe how the light output changes with input voltage. Because the resistance changes with temperature, and the temperature changes with power dissipation, the normal V^2/R equation derived from Ohm's law doesn't really work.

The power consumed by a lamp is proportional to V^1.5

The light output of the lamp is proportional to V^3.5

The life of the lamp is proportional to V^-13

If you increase the voltage to a lamp by 10%, the power consumed will go up by 15%, the light output will go up by 40%, but the life will go down by 70%

If you were to compare a single 100W bulb to the output of 2 100W bulbs run at 50W each, the 100W bulb would produce about 2.5x the total light output of the pair of half power bulbs. A 100W bulb so dimmed will consume 50W of power, but will produce the light of an undimmed 20W bulb. Less power in, but far less efficiency; you are better off with a smaller bulb unless you like the color.

The dim bulbs also have much longer life, which can be a signficiant benefit.

iwire: you might consider looking at some of the LED bulbs; some are rated for 120V, and probably some rated for outdoor use. There is quite a bit of BS in the market, where the light output gets inflated in the advertising but not in service... but if you only need a little bit of light they are great.


#55696 09/03/05 11:36 AM
Joined: May 2005
Posts: 706
I might go for the line of less-power-use except that the dimmers are throwing off heat.


#55697 09/03/05 11:56 AM
Joined: Jan 2003
Posts: 4,391
Dave, yes even new dimmers make heat and yes that is wasted power.

However the heat given off by a solid state dimmer will be far less than the heat and light that the lamp will not be giving off.

I agree as always there is much marketing hype to get by.

For your own piece of mind put a clamp meter around the line side of the a dimmer and cycle the dimmer up and down, you will see the current cycle to match.

Jon, sometime I will put a more efficient light at the back door, the big floods are there to light a large patch of driveway. However dimmed down they do a nice job to. [Linked Image]


Bob Badger
Construction & Maintenance Electrician
#55698 09/03/05 12:10 PM
Joined: May 2003
Posts: 2,876
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Mark Heller
"Well - I oughta....." -Jackie Gleason
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