Halogen uplighter electricity usage

[David Hearn]

We have a 300W halogen up-lighter with built in dimmer. It also has a

50W bendy spotlight with dimmer.

I'm aware that 300W is a lot of electricity, and in fact, it's too bright when on full - we tend to have it on 50% or less.

Does dimming a light reduce the electricity usage? Part of me says yes, but another part of me is less sure.

I'm thinking of looking for a 150W lamp to go in there which would be more reasonable - especially if dimming has little effect on electricity consumption.

Thanks

D

[gentlegreen]

I'm thinking yes - after allowing for triac voltage drop - though it wouldn't be directly in proportion to the reduction in light because incandescent lamps are less efficient at low power (and below their design current ? ).

.

[Harry Bloomfield]

David Hearn was thinking very hard :

A lamp is at its most efficient cost v light output at its full brightness. Dimmed it will certainly use less electricity, but the reduction would not be as much as you would get by simply reducing the lamps wattage.

[fred]

In article , David Hearn writes

I know that the efficiency of incandescent lamps falls off rapidly with decreasing drive, particularly for halogen lamps but I didn't want to just say 'it's shit' without an authoritative reference.

Not much, or should I say too much on google, the closest I could find in a quick search was an efficiency study of halogen torch bulbs by a caver:

the theory scales up it suggests the following:

300W at full brightness costs 300W (100% _relative_ efficiency) Dimmed to half brightness costs 230W (65% rel eff) Dimmed to quarter brightness costs 170W (65% rel eff)

ie. your savings are not great.

Your 150W bulb will hopefully give you the equiv brightness the half dimmed case but for 80W less.

150W dimmed to half bright costs 115W (65% rel eff) and should be equiv to the 300W 1/4 dimmed case but at 55W less useage.

HTH

[fred]

In article , fred writes

correction, 45% rel eff for 1/4 drive

[Andrew Gabriel]

My parents have a 500W one. They often run it in the evenings with a light output equivalent to about a 40W bulb. I stuck a true power meter on it, and at this level it was consuming 300W.

Yes, but not by much in comparison to drop in light output.

I think 200W is the smallest you can get that type of bulb, but that rating isn't common and you might have to search. The 100W and 150W ones are shorter.

[David Hearn]

I did a quick search last night and found one place which sold (I think)

118mm 150w bulbs and shorter 150w bulbs.

Just searched again and found a different site:

lists 150w 8mm x 78mm and 150w 8mm x 118mm (and 300w 8mm x 118mm +

500w 10mm x 118mm). D

[chris French]

Yeah I replaced the 500W bulb in the outside floodlight with a similar length (118mm I guess) 150W one

don't remember where I got it but it wasn't hard to find.