12v vs 240v lamps

[Trevor Smith]

Could anyboby explain why the 12v 50w halogen lamps I have in my kitchen appear brighter than the 240v 50w halogen Par 20 lamps I have fitted in the lounge?

[BigWallop]

Higher colour value. Whiter light. Dichrioc prismatic diffusion.

[Richard Head]

Its all to do with the filament size. On a 12V lamp the filament guage is much lower and the filament winding diameter is larger, and there are fewer turns so:-

1) More exposed surface area so more light can escape from the confines of the filament and 2) A 12V filament is far more robust and will last longer

[Rod]

I don't get that.

In both cases 50W of heat and light is being emitted by the lamp.

So the issues are surely:

o The proportions of heat to light;

o The colour.

The colour depends largely on temperature, and at a higher temperature there will be more light/less heat - so not wholly independent.

(I have not even tried to work it out, but while the 12V is a thicker filament, isn't the 240V one longer? So which really does have the larger surface area? Or effective surface area?)

Of course, if they are not running at exactly the specified voltage, then all bets are off!

[John Rumm]

Ah, a charm school graduate I see...

I expect by "colour value" BW probably meant CRI, which is indeed higher for a 12V halogen, and the light is certainly whiter. Many 12V lamps also have dichroic reflectors that also enhances the whiteness of the light by allowing some of the redder end of the spectra to escape out of the back of the bulb...

So I don't think you can really say "bollocks" unless it was of course a prelude to what you were about to follow it with.

Not that convincing really, also missing the more relevant point that the more robust filament can be run at a higher temperature which yields the aforementioned whiter light, and an increase in efficiency (i.e. more lumens per watt) which is why it not only appears brighter for the same power consumption, but in reality *is* brighter.

true, but not relevant to the question

[Trevor Smith]

Thankyou for the replies, I didn't think the dichrioc reflector had much to do with it as both lamps have them but when you look at the capsual the 12v one is a lot brighter. I just done a bit of quick maths and the 12v 50w lamp draws 4.16 amps and the 240v 50w lamp draws 0.208 amps so I gather more amps = more light.

[Andy Champ]

I don't know the correct answer, but that definitely isn't it. (I'd _guess_ the 12v is running at a higher temperature, which gives better efficiency but shorter life)

Andy

[John Rumm]

The mains halogens typically don't have dichroic reflectors and use ordinary opaque aluminium "silvering". That is also why they project more heat forwards.

Partly, more amps in this case translate to a higher filament temperature which gives more light.

[Harry Bloomfield]

John Rumm brought next idea :

Plus the fact that lower voltage means a shorter and more compact filament, which enables a better focus of the beam.

[Adam Aglionby]

GU10 lamps are aluminised reflectors, rarer GZ10 has a dichroic `cold mirror` and chamfered corners on lamp base to supposedly stop interchanging with GU10.

Both are spawn of the devil , LV halogen makes much more sense any way you look at it.

Adam

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[The Natural Philosopher]

Actually its simpler:

Bigger filament=runs hotter without melting = higher colour temperature= whiter light.

[The Natural Philosopher]

half right. More efficiency, but longer life. I suppose the element, being thicker, abardes away more slowly.

But its a fact. 12v lamps outlast 240v ones by about 10:1

[Dave Plowman (News)]

Far too broad a statement. Lamps last according to design and use. The most common 12 volts bulbs we see are in cars - and they certainly don't last 10 times longer than 240v. Nor do normal LV domestic ones.

[Man at B&Q]

Well, with a name like Dick Head...

MBQ

[The Natural Philosopher]

My LVs do.

I assumed we were talking halogens.

12v 50W halogen replacement frequency is about 10% of 240v 50W halogen.

[Dave Plowman (News)]

Not so here. By far the longest lived lamps out of all I have are PAR 38s. The halogen R80s seem pretty good too.

[dennis]

They probably last longer due to the electronic transformer having soft start.

[Adam Aglionby]

[e-mail]...

I`ve got some good quality Osram LV MR16s run off a Mode ,soft start, electronic trafo gone past their 12th Birthday in a frequently used bathroom.

Adam

[Dave Plowman (News)]

You can get soft start dimmers for 240v too.

[Tim S]

Dave Plowman (News) coughed up some electrons that declared:

GET Ultimate touch dimmers are soft start, because I've just tried one :)

Cheers

Tim