Hi I was thinking of putting some 12 volt 50 watt halogen lights in a
display cabinet as I thought that they would use less power than 240 volt 50
watt lights but was told that the opposite is true. Could someone tell me
how I could work out the power consumption so that I could compare mains and
low voltage lights?

Thanks Tracy

"Tracy" wrote in message
. uk...
Hi I was thinking of putting some 12 volt 50 watt halogen lights in a
display cabinet as I thought that they would use less power than 240 volt
50 watt lights but was told that the opposite is true. Could someone tell
me how I could work out the power consumption so that I could compare
mains and low voltage lights?

Thanks Tracy



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

Tracy wrote:
Hi I was thinking of putting some 12 volt 50 watt halogen lights in a
display cabinet as I thought that they would use less power than 240 volt 50
watt lights but was told that the opposite is true. Could someone tell me
how I could work out the power consumption so that I could compare mains and
low voltage lights?


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


--
Grunff

Tracy wrote:
Hi I was thinking of putting some 12 volt 50 watt halogen lights in a
display cabinet as I thought that they would use less power than 240 volt 50
watt lights but was told that the opposite is true. Could someone tell me
how I could work out the power consumption so that I could compare mains and
low voltage lights?

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.

"Ian Stirling" wrote in message
...
Tracy wrote:
Hi I was thinking of putting some 12 volt 50 watt halogen lights in a
display cabinet as I thought that they would use less power than 240 volt
50
watt lights but was told that the opposite is true. Could someone tell me
how I could work out the power consumption so that I could compare mains
and
low voltage lights?

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
240 volt light, disregarding what is used by the transformer.

Thanks Tracy

"Tracy" wrote in message
. uk...
Hi I was thinking of putting some 12 volt 50 watt halogen lights in a
display cabinet as I thought that they would use less power than 240 volt
50 watt lights but was told that the opposite is true. Could someone tell
me how I could work out the power consumption so that I could compare
mains and low voltage lights?


50W is 50W - it makes no difference whether 12 volt or 240 volt.

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

Tracy wrote:

"Ian Stirling" wrote in message
...
Tracy wrote:
Hi I was thinking of putting some 12 volt 50 watt halogen lights in a
display cabinet as I thought that they would use less power than 240 volt
50
watt lights but was told that the opposite is true. Could someone tell me
how I could work out the power consumption so that I could compare mains
and
low voltage lights?

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
240 volt light, disregarding what is used by the transformer.

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

In article ,
Ian Stirling writes:

LED is almost there - maybe another 5 years.

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.

--
Andrew Gabriel

Andrew Gabriel wrote:
In article ,
Ian Stirling writes:

LED is almost there - maybe another 5 years.

I'm not convinced -- there's a limit to how long they can keep saying
"maybe another 5 years" and not delivering.

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
In article ,
Ian Stirling writes:

LED is almost there - maybe another 5 years.

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.

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.

--
steve

Andrew Gabriel wrote:
In article ,
Ian Stirling writes:

LED is almost there - maybe another 5 years.

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

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.

Jason wrote:

50W is 50W - it makes no difference whether 12 volt or 240 volt.

Agreed.

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 ;-)

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).

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Steven Briggs wrote:
In message , Andrew Gabriel
writes
In article ,
Ian Stirling writes:

LED is almost there - maybe another 5 years.

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.

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.

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

http://cgi.ebay.com/White-Cree-Xlamp...11 0061896093
for example.

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

Adding in phosphors to make it 'cool white' will take it back to around
50-55lm/W.
This is pretty much bang on your current average CFL efficiency.

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.

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.

declared for all the world to hear...
Hi I was thinking of putting some 12 volt 50 watt halogen lights in a
display cabinet as I thought that they would use less power than 240 volt 50
watt lights but was told that the opposite is true. Could someone tell me
how I could work out the power consumption so that I could compare mains and
low voltage lights?

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

Vortex wrote:

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

Both will therefore have the same power consumption.

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.


--
http://gymratz.co.uk - Best Gym Equipment & Bodybuilding Supplements UK.
http://gymratz.co.uk/polar-heart-rate-monitors/ Polar HeartRate Monitors
http://fitness-equipment-uk.com - UK's No.1 Fitness Equipment Suppliers.
http://water-rower.co.uk - Worlds best prices on the Worlds best Rower.

""Pet @ www.gymratz.co.uk ;¬)"" wrote in message
k...
Vortex wrote:

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

Both will therefore have the same power consumption.

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.


--
http://gymratz.co.uk - Best Gym Equipment & Bodybuilding Supplements UK.
http://gymratz.co.uk/polar-heart-rate-monitors/ Polar HeartRate Monitors
http://fitness-equipment-uk.com - UK's No.1 Fitness Equipment Suppliers.
http://water-rower.co.uk - Worlds best prices on the Worlds best Rower.

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