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Home lighting - when is watt a watt?

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Home lighting - when is watt a watt?
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Veteran Member
Join Date: May 2004
2008-05-05, 21:28

Alright, I know a few of you will have an answer to this.

Where I live we're phasing out incandescent bulbs. Seeing as we're doing a little home remodeling, I think it's the perfect time to change the lightings system.

Pots lights for the low ceiling areas and track lighting fro the high ceilings. The question is, do we go low voltage or line voltage?

I read in some places that low voltage is more efficient, but is that really true. If I hook up a 35 watt bulb doesn't it use up the same amount of electricity whether it's part of a 12v or 120v system. The service coming into the building is 120v, a transformer has to step that down to 12v, on the output end, but the bulb still uses 35 watts, wouldn't both a line or low voltage system use the same amount of energy if they had the same number of (same rating) bulbs?

Granted there are plenty of variatios in intensity of light, but I'm not so sure that low voltage lights are that much brighter that significantly lower wattage halogens could be used?

Rocket Surgeon
Join Date: Feb 2005
Location: Whitby
2008-05-05, 23:25

Indeed you do use 35W whether it's 12V, 120V or 1200V. But the efficiency (lumens/watt) may be different - typically 15% more efficient in low voltage applications. That's what matters. Low voltage 12V stuff frequently has a good efficiency...but the transmission difference really matters. You need some heavy duty cable to send 12V any kind of distance.

Having said all that, you'll probably get more lm/W from fluorescents. That's assuming, of course, that you don't care about colour rendering, can't see the flicker* and don't mind if they look kind of ugly.

LED might be interesting, but probably not *quite* ready yet for prime time. Soon, though.
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Formerly turtle2472
Join Date: Mar 2005
Location: Tidewater Virginia
2008-05-06, 08:45

I'm looking forward to the improvements in LED lighting. I've read an article recently that did a cost analysis on them based on current prices and it ended up being pretty close to the same cost as a incandescent bulb over the lifespan. I think the bulbs were around $150 each but lasted near forever.

The big problem was the coloring it created. That's the main focus on getting them more into the mainstream market. It'll be nice once these are in place and putting out good color.

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Veteran Member
Join Date: May 2004
2008-05-06, 11:25

I've been learning all about the variations in home/stage lighting tech. Crazy stuff.

I'd love to go fluorescent in the kitchen/bath/hallway areas. My problem is I see flicker and I hate it. I know people say the frequency is too high to see, but from my reading that's not really true. The areas of the eye responsible for peripheral vision can be quite sensitive to flicker, so you can get the effect from your fill light. New generations of retrofit CFL are supposed to come in more pleasing colour temps and have less noticable ultra high frequencies.

I wonder how well it works.

The other weird thing is that most of the CFL solutions are retrofit to Line Voltage 120v fixtures - GU10, PAR16, etc - and not really available for Low Voltage 12v - MR16, GU5.3, MR11. Isn't fluorescent tubing essentially low voltage in operation? I wonder if it requires higher voltage on start up and so won't work with most low voltage fixtures unless we have special transformers.

LED retrofits exist for both, but the more affordable stuff is not quite there yet for consumer applications.

Veteran Member
Join Date: Oct 2004
Location: Leiden, the Netherlands
2008-05-06, 16:14

Don't forget that when you decide to go with 12V Halogen, the transportation loss is much higher (lower voltages need more current to transport the same amount of energy, because of Ohm's law, hence the need for thick cables as pointed out by Bryson). So any efficiency you might gain from the higher light yield, maybe lost in the cable.

A.f.a.i.k. fluorescent light requires very high voltages in order to create what is essentially a plasma.

From Wikipedia:
Fluorescent lamps are negative differential resistance devices, so as more current flows through them, the electrical resistance of the fluorescent lamp drops, allowing even more current to flow. Connected directly to a constant-voltage mains power line, a fluorescent lamp would rapidly self-destruct due to the uncontrolled current flow. To prevent this, fluorescent lamps must use an auxiliary device, a ballast, to regulate the current flow through the tube; and to provide a higher voltage for starting the lamp.
While the ballast could be (and occasionally is) as simple as a resistor, substantial power is wasted in a resistive ballast so ballasts usually use an inductor instead. For operation from AC mains voltage, the use of simple magnetic ballast is common. In countries that use 120 V AC mains, the mains voltage is insufficient to light large fluorescent lamps so the ballast for these larger fluorescent lamps is often a step-up autotransformer with substantial leakage inductance (so as to limit the current flow). Either form of inductive ballast may also include a capacitor for power factor correction.

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