My brother’s an electrician and i’m a psychologist, so he should
be right about this and I should be wrong. I recently moved into
a house that has 12 volt halogen lighting which coexists with
conventional (for Australia) 240 volt wiring. Compact
fluorescents have become popular in the last 10 years in Oz.
These allow you to use a bulb in the 240 volt sockets that uses
about 1/7th the energy of conventional incandescent bulbs. For
example a 13w compact = a 100 w incandescent, 11w compact = 75w
incandescent etc.
I said that we should use the compact fluoros in preference to
the 12v 50w halogens, 'cause 13w is less than 50w therefore
significant energy savings. He said that the 12 volt circuit will
always use less power and therefore reduce our energy bill. But
power is watts, right? Can you shed some light on this Cecil, and
stop the sparks flying in our family meetings.
I’ve never seen a home with 12V wiring. How does it work? Is there a transformer somewhere in the house?
If the 12V is generated from the 240V, then yes, you are correct. 13W is less than 50W, and that should be the only concern. However your brother could be correct if the 12V line had a separate meter, and the cost per watt-hour is higher on the 240V line. That sounds very unlikely though - long distance power transmission uses very high voltages so it should be more expensive to get lower voltage.
scr4 is correct- the actual power is what matters, not the voltage or current. The 12V probably comes from a transformer in the house connected to the 240V. A way to explain it to your brother is that the transformer has a 20 to 1 turns ratio - which means that it steps 240V down to 12V. This means it steps current the opposite way. The 50W halogen light draws 50/12 = 4.2 amps, which is lowered to 0.21 amps on the 240V volt side. This action means that the voltage times current product (which = power) is the same on both sides of the transformer- required for a passive device that can’t add energy!
Compare that with 13W at 240V, which is only 0.054 amps. Some electricians think more in terms of amps than power, which is usually ok if the voltage is always the same (i.e. 240V, or 120V in the US). It gets them into trouble when comparing two different voltage systems!
I don’t know about Australia, but in the US, we pay by the watt. If a device uses 13 watts, it’s going to be cheaper to use than one that uses 100 watts.
Also, halogen lights put out more heat than compact fluorescents. Your AC will have to run longer to cool off the extra heat put out by the halogens. Switch to CFs, and you lower your cooling bill.
The wattage is what you have to look at, since that is the power used .
P=V*I
Where P=power I=current(amps) and V=voltage
Power is sold by the kilowatt hour.
A light bulb that is a 100 watt bulb will consume one killowatt hour in ten hours. This is reguardless of the voltage at which the power is consumed.
To compare which is more efficient you have to look at the lumens output for each bulb and it’s power used.
Lumens are the unit of measure for light sources.
You need a common unit to compare the different lights. Try Lumens/watts=number of lumens per watt used. The higher the lumens per watt used the more efficient the bulb.
This doesn’t account for the greater resistance to power flow at a lower voltage. In otherwards the wiring in the home after the power step down. If you are using 12v DC for these lights the resistance over distance is even greater.
I’m only your wildest fear, from the corners of your darkest thoughts.
No offense Jmac but your brother’s insane. A halogen bulb is just a special kind of incandescent. They are a little more efficient, i.e. they put out more lumens per watt, and they last alot longer than regular bulbs but they don’t even come close to the efficiency of flourescents.
I for one welcome our new insect overlords… - K. Brockman
Saftey note on hallogen bulbs. They require that you have ultraviolet filters over the bulbs and they must have a saftey shield to prevent injury if they shatter. They also run very hot and need shields to prevent fires from items touching them. This doesn’t mean the other lights won’t be a fire hazard if something sets against them.
Murcury vapor lights can also produce lots of ultraviolet light if the bulbs are damaged, but still light.
I’m only your wildest fear, from the corners of your darkest thoughts.
Echoing Hail Ants’ remark; I am told by a pro decorator that halogen bulbs are popular because of the color of light they produce; electrical or any other efficiency having little to do with it. Halogen light = white; incandescent light = pink; flourescent light = green. - MC, still (sigh)
I have never seen one transformer for an entire house. Each Halogen fixture has it’s own transformer, or a transformer for a group of lights near each other, that resistance over a length of wire thing. Halogens are bright for their physical size,they are also resistant to vibration and jarring. The breakage, hah, explosion thing , is cause they are so hot, a weak area in the glass or oil on the glass and POW! Also doesn’t the transformer itself use some watts? I tried to tell from your post, ARJ, but I can’t remember my formulae. Transformers generate heat I know that.
It is really impossible for us in the US to give a definate answer to jmac. Aside from the voltage differance, instead of emitting light, the bulbs,due to the coriolis effect, absorb darkness,down under. This is another reason to place protective filters over Halogen bulbs, they are so powerful that the darkness moves much faster than normal, often passing through the bulb, it hits the reflector and is bounced back into the room. The filter can prevent this so called boomarang effect.
“Pardon me while I have a strange interlude.”-Marx