low voltage halogen lights power consumption

The Watt is a measurement of power: The amount of energy used per second.

Both will therefore have the same power consumption.

The halogen lights will however appear brighter..for a given Wattage because they are more efficient.

david

The clue is in the name - a 50W bulb uses 50W, regardless of whether it's a halogen, GLS or CF.

The key is in the name. "50 watt". This is the power use. In practice, they will use a bit more than this at 12V, as the transformer wastes some.

The 12V ones may produce slightly more light however, but not much, due to construction reasons.

The only way to reduce power use is to go to fluorescent. LED is almost there - maybe another 5 years.

So a 50 watt 12 volt light uses the same amount of electricity as a 50 watt

Thanks Tracy

One thing I would mention, is that 50W halogens in a display cabinet would be pretty bright and would get very hot. 20W or even 10W may be more suitable. With tighter beams from smaller bulbs, you could still light up your display items nicely, and without the need for sunglasses ;-)

-- JJ

Pretty much. Though the 50W 12V light may produce slightly more light, dut to the physics of things.

I'm not convinced -- there's a limit to how long they can keep saying "maybe another 5 years" and not delivering. When they do become viable technically, you have to wait another 15-20 years for the remaining patent lifes to expire so they can be manufactured at commodity pricing and become mass market.

My guess is that in another 5 years, we'll have something based on HID headlamp technology replacing MR16's, not LEDs.

Is there? :) LEDs are the future has been said at least since the 70s, but they still arent there, and wont be any time soon. Some things some people will swallow over and over.

NT

In message , Andrew Gabriel writes

Jeez, that makes me think back. It's 5 years since I started work for a company designing drivers for the early Lumileds stuff. I always doubted the marketeers projections of future efficiency gains. I reckoned the big breakthroughs had been made with package design and light extraction from the die. Yes we've got more light output now, but mostly from larger/parallel/series dies to give 3W & 5W parts. There is still a basic problem of keeping them cool enough if you want a lot of light, poor colour rendition, and what always put me off which is the point source intensity of the things, spots before the eyes job.

In the last 4 years, it's gone from (commercially available) power LEDs doing 20lm/W, to 60lm/W, at pretty much the same price point. A tripling in efficiency.

That is actually competing directly with fluorescent in terms of efficiency.

(other points answered in other post.

Yup, 20W is probably ample.

You would also be much better of with the 12V ones for display work than the 240V ones. Reasons:

Better quality of white light

Improved specular reflections (makes stuff look bright and shiny - which is why shops use them for this so often)

In 12V you can get "dichroic" bulbs that in addition to giving better colour, also radiate less heat forward (more of it escapes through the back of the fitting, and less will end up in the display case

The bulbs last longer and are more resistant to vibration (caused by opening / closing doors on the case etc).

Well - that's 60lm at one watt, minimum, in parts available now, compared to lumileds first 3W offerings which were also 60lm IIRC.

IIRC the bin he's offering is 67lm/W minimum.

Adding in phosphors to make it 'cool white' will take it back to around

Well - it is a halogen replacement in terms of beams, not a CFL replacement.

Though you can add diffusers easily enough.

For _small_ lights - 1W, (3W halogen equiv), it's pretty much a no-brainer, the LED chip can hit 75C while staying 90% as efficient as at 25C, and a heatsink that does 40C/W can be quite small.

For larger lights it's harder. To make something that puts out as much light as a 22W/100W CFL tube, in the same form factor is going to involve lots of heatsink.

There are higher power versions, that can be driven harder, and produce more light, but these are considerably less efficient.

At the moment, the lighting system I outlined for your hypothetical kitchen to replace 10*50w LV halogen spots (producing the same amount of light, at around a third of the power) will cost maybe 10-15 times that of a halogen install.

And will never usually need a bulb change.

snipped-for-privacy@yahoo.co.uk declared for all the world to hear...

In my day power in Watts is current x Voltage. A 50 Watt bulb will consume 50W, regardless of the technology it employs.

Agreed, but the 12v ones will incur a greater power loss through the heat and noise(vibration) of the transformer which is guaranteed not to be 100% efficient.

Besides which... I'd suggest a max. of 20 or 25W LV bulbs in a display cabinet. 50W / bulb is way OTT for for such a purpose IMHO.

I installed some 20W halogen "under cabinet" lights in our kitchen that use small switched mode PSU's.

One small PSU servicing 60 watts of light and only just warm to the touch. I guess 40 degrees.

I guess here energy loss due to PSU inefficiency is actually far smaller than light gain using LV Halogen in preference to conventional.

David