On 12v vs 240v

[BeeLZeebub]

I'm filing this under "things I always wanted to ask ... but".

I see that some multi-arm chandeliers have built-in transformers that use 10w G4s @ 12v. Given that low wattage GU10s run off 240v, what is that prevents G4s doing likewise? Is it that the reciprocal resistance of the filament would be implausible for the G4 under 240v? Due to physical size constraints? I'm assuming that you can't buy 10w G4s @240v? ... otherwise light manufacturers wouldn't fit transformers, no? ....

There's no 'smoking gun explanation' on the web so I'm aware that I may have a garbled understanding of the issue. If someone sufficiently bored could take a minute to explain ....

 

[ban-all-sheds]

http://www.ebay.in/itm/5-pc-230V-20W-G4-base-JC-bi-pin-halogen-light-bulb-lamp-/250785458639

 

[BeeLZeebub]

Hmm, OK - so they exist. So it begs the question as to why fittings like this (for eg):

http://www.weybridgelights.co.uk/lighting/Jogg-12-Arm-Pendant-Light.html

bother with a built-in transformer. Is the fact that your G4 example is from Hong Kong evidence of their scarcity over here? If so, can anyone say why?

OK ... I know this is far from being a sexy subject .....

 

[RF Lighting]

Because you get a better light from a 12V lamp than you do from a 230V lamp of the same wattage.

 

[SUNRAY]

Because you get a better light from a 12V lamp than you do from a 230V lamp of the same wattage.

 

[bernardgreen]

With incandescent lamps a 12 volt lamp can have a much shorter ( but thicker ) filament allowing for the glass envelope to be smaller. Only really useful in projectors and other equipment where focusing of the light is required. For some decorative lamp holders a small lamp is necessary.

Big drawback of 12 volts is the higher current for the same "brightness" which increases wire diameter and limits distance between 12 volt supply and the lamp(s).

While properly installed 12 volt lamps may reduce the hazards of electrical shock the higher currents involved may increase the risk of overheating of 12 volt wiring if it is poorly designed and/or installed.

 

[ericmark]

bernardgreen is spot on as usual however I would add that we don't use transformers but inverters which control the RMS voltage to very fine limits so in theroy the 12v lamp lasts longer then the 230v lamp equivalent.

However in practice a 12 volt lamp blowing can also take out the inverter so there is not real gain unless in the area where it is used one has unstable voltage supply.

One of the major problems is the small spot lamps used with low voltage don't have different sockets for Dichromic and non Dichromic lamps. With 230v we have GZ10 for Dichromic and GU10 for non Dichromic so you can use a non Dichromic in a GZ10 holder but not visa versa.

The other problem is wattage with 12v the wrong size lamp can't be used without damage to the inverter both too big and too small of a lamp causes a problem as inverters have both a max and min wattage. So often one can't fit LED lamps as they don't use enough power.

Added to that florescent and cold cathode lamps will not work with 12 volt they are only available in 230 volt versions. (Sure there must by now be an exception but would guess very expensive)

When I changed my lights I was very careful to select one which could use discharge lamps. I moved from a 3 to 5 bulb fitting so I could fit small 8W lamps and still get same light. So in real terms I have since I moved into the house reduced the power used by living room lights from 120W to 80W not really that much of a saving.

Yes I do have 12 volt lighting in the bathroom but that was purely as they came at the right price (zero) I would not normally use 12 volt lighting.

 

[BeeLZeebub]

Thanks for indulging me guys .... it's fairly clear from your responses that the benefits of 12v lighting viz 230v are at least equivocal. So it's interesting that the industry has developed as it has ... can the perceived benefits of 12v be such that one of the sheds' importers hasn't called a chandelier manufacturer and said, you know, I could save you a fortune having to incorporate (ugly) transformers in your fittings by our importing a load of BASs 230v G4s from Hong Kong ......?

 

[ericmark]

Having lived in Hong Kong for 5 months likely that has happened we are about two years behind them.

However it is our climate which has resulted in systems not used else where. Go to Turkey for example and nearly all lighting is of the discharge type. In a hot climate far better never to heat something up than to try to cool it once heated up.

However winter means far more use of lighting than in Turkey and Summer means far less use of lighting than Turkey. So we have traditionally used tungsten lighting to supplement our central heating. And in the past it worked well.

Convected heat is easy to measure and control but radiated heat warms the body rather than the air so we had a mixture of convected heat from central heating and radiated heat from lighting which suited this country.

Countries further north needed far more heat in the Winter and as a result used heat exchangers and far less air changes than here. Also our unique position in the Atlantic gives us a far more temperate climate than others at the same latitude.

However as yet our government seem to have overlooked the fact we are unique and what works else where may not work here.

Manufactures make items for world wide sale and don't really design them specially for the UK.

This means us British have to use common sense when selecting what we want and have to take manufactures claims with a pinch of salt.

I still can't work out how a bulb which give out light and heat is less efficient to one giving out light and RF as we want the heat and don't want the RF and certainly don't want the waist products from discharge lighting when used indoors?