Ask Me Help Desk - Track lights: low voltage vs line voltage.comsume the same electricity in the end?

Hi! I just installed a section of track light in my living room just to see what it would look like and so far I'm not convinced... you see, I had a regular celing lamp with a 75w incandescent bulb and the room was very well lit... now with the track light I find that I need 3 fixtures with halogen bulbs each being 50w to get something similar to what I had before in terms of light and brightness!

My concern is that now I'm going to be spending double the electricity than I used to before with the regular incandescent bulb. In the store they say not to worry that since they are low voltage 12v halogen bulbs that they comsume a lot less than the same wattage incandescent bulb. Is this true? Is there a difference in electricity comsumption comparing this low voltage 12v halogens to line voltage halogens? Using them in the same wattage of course... lets say 50 watts.

I don't trust them in the store for a lot of them many times know less than us customers!:mad::confused:

Thanks in advance!

A 50-watt lamp at 120 volts consumes just over 0.41 amps of current. Another 50-watt lamp at 12 volts consumes 4.1 amps of current. We don't pay for volts (electromotive force) or amps (current), we pay for power (watts).

Consumers pay for watts! The meter on your house is a watt meter -- not a voltmeter, not an ammeter. If you have a 12 volt bulb that consumes 50 watts, it's still 50 watts regardless of the voltage or current it's using (Watts = Volts * Amps). If you need three 50-watt bulbs, that's 150 watts of electric power. If you compare that with one 75-watt bulb and you can see that you're using twice the electricity (There's also a small additional amount of power that's consumed in the transformer and lost as heat).

They're not telling you the truth. You were quite correct in your analysis.

There would be a major difference if the reflectors are spots vs. floods.

Dear sir/madam

By installing helogen instead of incandescent bulb you could get more foucas spots and as well as better look[decoration] for the place you are installing.

Actually if you use them inteligently you might ended up using less power for the instead if you use only one helogen most time or two, there might be chance that you have to use thired one only for the decorative purpose.

Hance instead of using one 75w incandescent bulb you might use only 50W helogen most of the time and save the power.

If you really want to save power and enhance the visibility[Lux] you can use flourocent or CLF bulb [white light bulb] instead of incandescent bulb or the helogen.

Use head and think first what you want and how you want and decide

:cool:

A 100 watt circuit uses 100 watts no matter what the voltage. A 100 watt light operating at 120 volts uses the same energy as a 100 watt light operating at 12 volts. 100 watts.

With lighting, you are looking for less watts per lumen. (A CFL uses less energy to produce the same amount of light, that is where you get a cost savings.)

Am I missing something?
Could we please discussed this.
We pay electricity by the power we consume. Since the volatge is fixed (for exaple: 120V), we pay for the current(I) we consume.
A 50W bulb on a 12V circuit will consume 4.1 Amp
A 50W bulb on a 120V circuit will consume 0.41 Amp
So we will pay electricity 10 times more for the Halogen lighting (12V).
(although it will produce 10 times more light... )
(I disregard the power wasted on the transformer for the 12V)

Am I right here?

And that is just for the electricity consumption issue. I feel the original question was also regarding the light efficiency. In this issue I think the "reflector" type Halogen lights are such a waste compared to their free bulb version. One can lit a whole room with a bulb of 12V 20W halogen, but with it is inside a reflector packaging it lights just the corner...

Quote:

Originally Posted by ar57

Am I missing something??
Could we please discussed this.
We pay electricity by the power we consume. Since the volatge is fixed (for exaple: 120V), we pay for the current(I) we consume.
a 50W bulb on a 12V circuit will consume 4.1 Amp
a 50W bulb on a 120V circuit will consume 0.41 Amp
So we will pay electricity 10 times more for the Halogen lighting (12V).
(although it will produce 10 times more light...)
(I disregard the power wasted on the transformer for the 12V)

Your first statement is correct. The utility charges you for POWER, which is is energy over time, and is measured in watt-hours. If you burn a 100 watt light for an hour, you have used 100 watt hours of power.

Watts =volts x amps:
12Volts x 4.1Amps =50 watts
120Volts x .41Amps =50 Watts

In physics terms, energy is conserved. Since time is a constant, power is also conserved. 50 watts for an hour is 50 watt hours, no matter what the voltage and amperage.

If you lower the voltage, you must increase the amperage to get the same energy.

But with lights, what really matters is LUMENS, which is the measure of light intensity. You want to decrease the watts to lumens ratio.

If you can convert more of the energy into light (and less into heat) you achieve a cost savings. For example, a typical CFL uses about 13 watts to produce the same amount of light as a 60 watt incandescent lamp.

Other ways to increase usable light are fixture placement, reflectors to direct the light where you need it, and keeping the fixture clean. (I'm an industrial maintenance electrician, and I always clean the fixture every time I re-lamp)

Quote:

Originally Posted by ohb0b

Your first statement is correct. The utility charges you for POWER, which is is energy over time, and is measured in watt-hours. If you burn a 100 watt light for an hour, you have used 100 watt hours of power.

Watts =volts x amps:
12Volts x 4.1Amps =50 watts
120Volts x .41Amps =50 Watts

In physics terms, energy is conserved. Since time is a constant, power is also conserved. 50 watts for an hour is 50 watt hours, no matter what the voltage and amperage.

If you lower the voltage, you must increase the amperage to get the same energy.

But with lights, what really matters is LUMENS, which is the measure of light intensity. You want to decrease the watts to lumens ratio.

If you can convert more of the energy into light (and less into heat) you achieve a cost savings. For example, a typical CFL uses about 13 watts to produce the same amount of light as a 60 watt incandescent lamp.

Other ways to increase usable light are fixture placement, reflectors to direct the light where you need it, and keeping the fixture clean. (I'm an industrial maintenance electrician, and I always clean the fixture every time I re-lamp)

Thank you very much for the knowledgeable answer. I’m really happy I think I found somebody that can make some sense in this confusing issue for me.
When I was in school (some 40 years ago) I seem to remember that we were taught that (ideal) transformer does not “consume” current. I mean if you draw an electrical circuit diagram with a transformer, the same current will flow on the input and output legs.
If this is the case and in one side (right) is the 12V 50W halogen bulb, then the transformer will consume 4.1 Amp from the main (on the other side of the transformer), thus “presenting” the 120V side with a 492 W lamp (120V times 4.1A).
Is this the case?
What I am asking actually is if we plug a normal 50W bulb and then disconnect and plug the 12V (through transformer) bulb, would this vertical-metal-wheel in the electricity meter turn in the same speed in both cases?
THANK YOU

It's P1=P2 or V1I1=V2I2 or in words:

Power(Primary) = Power(secondary)

or substituting any power formula e.g. P=VI

Voltage(Primary)*Current(Pri)= Voltage(sec)*Current(sec)

In your wheel example, if I read it riight, you want to keep the primary connected and disconnect the secondary and measure the power. In this case the power would be zero.

In an application of a transformer, there are eddy current losses which are very small.

Some 40 years ago where you said

Quote:

Originally Posted by ar57

“consume” current

it's really "consume power". Power is conserved. The power in the primary is the same as in the secondary.

If it wasn't conserved, it would be prohibitive for a power company to supply power at 10 KV and have transmissin lines greater than 100 K V. If that were the case, the utility would be broke if the transformers consumed power.

Quote:

Originally Posted by KeepItSimpleStupid

It's P1=P2 or V1I1=V2I2 or in words:

Power(Primary) = Power(secondary)

or substituting any power formula e.g. P=VI

Voltage(Primary)*Current(Pri)= Voltage(sec)*Current(sec)

Thank you very much. I now understand my error :o:o:o
I thought the current in a transformer is not the same at the primary and secondary circuits, and this is a mistake!! :o

Quote:

Originally Posted by OP

I thought the icurrent in a transformer is not the same at the primary and secondary circuits, and this is a mistake !!!

You still got it wrong. The current would be the same only if the primary and secondary voltages were the same which happens in an isolation transformer.

Power in = power out