Low Voltage Lighting?

[jungle_jim01]

Hi, i'm about to replace the lighting in my lounge. Someone suggested using low voltage lighting as an energy saving option, but i've read mixed reports online. Am i right in thinking that low voltage bulbs tend to be more efficient and much brighter than mains?
I also read about going through building regs! argh! wheras mains i could do myself...Any advice on this would be really welcome.

Thanks

 

[MdB]

First off, the most important bit - If you reduce the voltage by a factor of 20 (240V to 12V) then the current goes up by a factor of 20 for the same power bulb. This nominally means that your cable has to be over 20 times the thickness. Now normal lighting cable is typically many times thicker than it normally needs to be so the actual increase probably won't be as much but expect to have to use thicker cable. To calculate the actual thickness required, you need to read and understand the 17th edition regs. There is no rule of thumb as it depends on how the cable is fitted. You probably won't be able to use normal mains light switches either.

As for efficiency, 12V halogen are better than 240V halogen but both are poor when compared to LED or compact fluorescent. LED efficiency is likely to be similar for all voltage levels (I've not checked this) and compact fluorescent is likely to be better for higher voltage supplies (again I've not checked this).

Brightness of the bulb has nothing to do with its voltage supply. This just comes from how it was designed.

My very blunt answer to what mains work you could do yourself is that if you don't know the answer to that question then the answer is none. For example, tell me what thickness cable is required to supply 5 x 50W bulbs (not exactly great deal) when running at 12V? And yes, I haven't given you enough information to answer that question so what information is missing?

If you really want to do some of the wiring yourself, then get hold of one of the many books which describe what the 17th edition actually means. Read it and then decide if you understand enough to know what you are doing. Anything major though or work in the bathroom / kitchen will have to be approved by a Part P qualified person though.

 

[biffvernon]

Very true. There is the principle that you don't get out for nought so changing the voltage in itself is unlikely to be an energy saver.

But changing to LED lights (for which low voltage systems may happen to be appropriate) could be a significant energy saver.

(Not that your lounge lights use a lot - it's the cup of coffee you drink in there that counts.)

 

[MdB]

Personally, I think LED lights aren't there yet. The ones I have seen have too low a light output and are too expensive which implies that an awful lot of energy goes into their production.

 

[Flyfisher]

I'd say the quickest and cheapest way to more efficient lighting is to use CFLs, which give about 60 lumens/watt compared to about 17 lumens/watt for a 100W incandescent bulb. For this comparison, lumens just means 'amount of light', so in the above comparison a CFL will give about 3.5x the light of an incandescent.

From what I've read, LED lamps have a similar efficiency as CFLs, but they are quite a bit more expensive and are still being developed. They should be the longest lasting of the three types, so lifetime costs may look better than the initial purchase costs.

Interestingly, incandescent lamps are more efficient the brighter (hotter) they are (from http://en.wikipedia.org/wiki/Incandescent_light_bulb):

40 W tungsten incandescent 1.9%
60 W tungsten incandescent 2.1%
100 W tungsten incandescent 2.6%
glass halogen 2.3%
quartz halogen 3.5%

So if a room requires, say, 200 watts of lighting, it's more efficient to use 2x 100W bulbs than 5x 40W bulbs . . . except 100W bulbs are no longer freely available.

Low voltage Quartz Halogen bulbs are certainly more efficient than standard incandescents, but will require a lot more work if they are to replace existing mains incandescents. MdB has already mentioned that the wiring will almost certainly not support the higher currents involved, nor will existing switches, plus there are transformers to be hidden somewhere. This may not be a problem if done as part of a substantial re-decoration, but for simplicity just swapping existing incandescents for CFLs is the easiest option.

Of course, there are a whole set of other considerations when changing to CFLs such as colour temperature, warm-up times, dimming issues etc, quite apart from basic lighting efficiency, which probably explains why there is no generally agreed 'best' lighting solution.

My guess is that LED lighting will gradually rise to the top of the pile, assuming they can continue the development progress of recent years and get production costs down, but I think it's got a way to go yet before it becomes universally accepted.

 

[MdB]

Interestingly, incandescent lamps are more efficient the brighter (hotter) they are (from http://en.wikipedia.org/wiki/Incandescent_light_bulb):

40 W tungsten incandescent 1.9%
60 W tungsten incandescent 2.1%
100 W tungsten incandescent 2.6%

I would be interested to know why this is the case. I would have thought that they were all the same efficiency if operating at the same temperature (and I can't see why they wouldn't all be operating at the same temperature).

 

[Flyfisher]

I'm not sure, but I assume that 100W bulbs run hotter than 40W bulbs. Isn't that the basis of their operation? I've read somewhere that a manufacturer (Philips?) has produced higher-efficiency incandescents by reflecting/focusing some of the heat back onto the filament, which increases the operating temperature, which increases efficiency. I recall it was something like the light output of a 100W bulb but for only 70W of energy used.

I'd also guess increased operating temperature is the reason behind the increased efficiency of quartz halogen lamps. The halogen gas reduces filament vapourisation (I think), meaning they can be run hotter, hence the use of a quartz-based glass to cope with the higher temperature. I'm not entirely sure but that's my understanding.

 

[chuckey]

MDB, I think its all to do with the size of the element compared with the size of the glass envelope. This why the tiny quartz bulbs are so good and large envelope (for their power) are poor. 97% of the power is going to waste via the envelope, so half the envelope size, superficially only half the power would be required, however the filament is now closer to the envelope, so losses increase. . Clearly a dead end technology, no advantage to it what so ever, except for 200 million+ light fitting installed for them, they don't look too bad ( compact flourescents :roll: ), quality of light is also acceptable (LEDS :roll: ) Also the heat is only wasted if the light bulb is outside or is used in summer ( 8) .
Frank

 

[biffvernon]

Hmmmm...I reckon they do better when not put in an envelope.

 

[Penners]

I reckon they do better when not put in an envelope.

Well, the filament certainly burns brighter. Regrettably, it only does so for a fraction of a second.

 

[philpjuk100]

Hmmmm...I reckon they do better when not put in an envelope.

Not got an envelope big enough,will a jiffy bag do?

 

[FamilyWiggs]

Jiffy bags are fine - just make sure not to use a bushel.

 

[MdB]

Nah, I don't buy it.

A 50W bulb would have a filament a quarter as thick and half as long as that in 100W bulb if made from the same material and operated at the same temperature. That may have something to do with it. I guess a thinner wire may have to operate at a lower temperature to give a decent lifespan. Lower temperatures would change the colour profile though making it more red (and less efficient). I can't say I've ever noticed 50W bulbs being a different colour to 100W bulbs so if there is a difference in temp, it must be small.

The glass envelope needs to be as large as possible to reduce losses by conduction but otherwise doesn't play a part. The vast majority of losses are due to the radiated energy in the IR spectrum rather than in the visible. The envelope plays no part in this.


This is from the article linked from wiki http://www.ccri.edu/physics/keefe/light.htm:

The table below is for General Electric Standard light bulbs.
Watts Lumens L/W Efficiency
40 505 12.6 1.86%
60 870 14.5 2.13%
75 1190 15.9 2.33%
100 1750 17.5 2.6 %

Note that one 100 watt bulb puts out more lumens than two 60 watt bulbs and more than three 40 watt bulbs.

The last line is interesting...

If somebody has some 60W and 100W bulbs in the cupboard, it would be interesting to know what the Lumen values are (if marked).

 

[Flyfisher]

At least that source also supports the basic contention that higher wattage incandescents are more efficient. But if increased operating temperature isn;t the mechanism for this increased efficiency, what else is there that could?

I take your point about operating temperature affecting the colour temperature; my guess is that it is just not be noticeable. Don't forget that the human eye is remarkable adaptable - we don't perceive daylight as particularly blue or incandescents as particularly red (or fluorescents as particularly green).

So anyway, the EU bans 100W lightbulbs to conserve energy, people find that 60W bubs are not bright enough so they use two of them instead and not only consume 120W of energy but convert even less of it into light. Marvellous. Should have banned 40W bulbs to start with. :wink:

 

[biffvernon]

The glass envelope needs to be as large as possible

Well that would have to go in a jiffy bag...but what's the point?

 

[philpjuk100]

I know there are lighting experts on here so here goes- I have an old flourescent lamp behind the bressumer beam in my kitchen which lights up the wall in the inglenook,this contributes to the light in the kitchen,it went BANG! last week (it looks as if it is the choke) I was going to fix it with bits from another scrap lamp but now think there may be a better and "greener" way.It is used for two or three hours a day,a pair of spots could replace it,I think that halogen are out due to wattage and temperature(they are quite low and you could touch your ear on them!)I have an led unit in a stairway which is on all night but is not very bright and gives a "cold" blue light so I think that leaves CFLs.I have a couple of spots in the kitchen fitted with reflector CFLs but they are not very bright and seem to have a short life,both have been replaced in less than two years(Ikea screw in lamps).Is there an alternative? or would I be better fixing the original flourescent? (four foot)thanks,phil.

 

[MdB]

If you are looking for the green option, stick with what you have. T5 / T8 florescent tubes are just as efficient as CFLs (if not more so).
http://en.wikipedia.org/wiki/Luminous_efficacy#Examples_2

 

[philpjuk100]

Thanks,sounds good to me! (although I think I will replace it with a new one with a diffuser on to give it some protection).We were happy with the light from the flourescent. I know that in industry flourescents were said to be "free" light due to their leading power factor correcting all the inductive loads but in the domestic situation most of the main load is resistive.

 

[Penners]

Are flourescent lamps used in bakeries?

 

[philpjuk100]

No they use flour!(oh I get it!)phil.