Re: LV versus 240 halogen downlighters?

[Zymurgy]

> > Just had a look at some 240V halogen downlighters from B&Q. > > I have noticed that the bulb or rather the reflector part of it has > > diffrent color to LV 12V ones /240V clear , 12V slight colour shading/ > > You may have been comparing a bulb with an standard aluminium reflector > against one with a dichroic reflector. On the latter type, the reflector > reflective to most of the visible spectrum, but translucent for some > parts of it and also for most of the infra-red wavelengths. The > advantage is they do not project as much heat forward as the standard > aluminium reflector ones. The also tend to look slightly nicer for > display lighting as the slight colour staining you get from different > angles can look quite attractive.

Hmm, that's all well and good but how does the light look in real terms. I have LV and 240 halogens installed, the LV is clear white, the 240V have a yellow tinge and don't appear to throw out much light.

What is this dichroic of which you speak. are these whiter ?

Cheers,

Paul.

[John Rumm]

I think you are right - you get more light for a given wattage from the LV. Also you may find that with modern LV transformers (i.e. ones which are not transformers at all, but actually small switched mode power supplies) they will be less affected by local voltage sags and brownouts that can give the 240V cousins a yellow tinge.

You can get dichroic bulbs in LV and 240V although they are more common in LV. It just describes the way in which the reflector is designed. A standard bulb will normally have a metal (aluminium) coated reflector that reflects like a mirror - most of the frequencies of light (and hence infra red/heat) produced by the hot filament get projected forward. As a result you are stuck with the natural output spectrum of a discharge lamp - which is not very daylight like - giving the yellower light plus lots of heat.

The dichroic (literally "having two colours" or "two frequencies") reflectors allow some "colours" to pass through the reflector while reflecting others. This lets you "tune" or equalise the colour of the projected light and at the same time loose some of the projected heat (it is still generated but more is absorbed by the light fitting). Hence you get a different quality of light from them - making them seem more natural and whiter. They also tend to make for slightly more "specular" illumination. Hence shiny things seem more reflective and sparkly, which is why they are good for shop displays and spot highlighting in buildings.

[Zymurgy]

Excellent, thanks. Exactly what I wanted to know.

This ...

not very daylight like - giving the yellower light plus lots of heat.

Is exactly what I have.

I'll try new bulbs, otherwise the fitting is coming down. Even with

200W kicking out in the kitchen it's still dull in there.

Cheers,

Paul.

[Rafal]

What size is your kitchen? My is 3.40m X 2.40m, 2.70m high and I planned for 4 x 50W 12V lights. Looks like it may not be enough

[The Natural Philosopher]

for really bright light, use anout 25W/sq meter. Which means you need about 8 50W spots.

You will get by with 4 tho.

[Rafal]

Thank you. I was looking for same sort of W/sqm figure and I definitely like a lot of light. One more question.Came across opinion that electronic /switched mode/ transformers are prone to overheating inside of well insulated /packed wool/ ceilings and switching off for cooling or failing. Is it true? All my celings are well insulated. Rafal

[The Natural Philosopher]

Both types will overheat if stuiffed inised insulation. You need to create a (supposedly fireproof) box these days with enough airspace round the light to allow the heat to come down to the plasterboard..

Transformers of eother type should be outsdie that box, and in a cavity of their own.

It is NOT normal to insulate between floors of a house. Only the top floor ceiling is normally insulated. Here in my case I have boarded the loft, and teh transformesr (toroids) sit on top of teh bioardin in a nice cool breeze.

If not dimming, I recommend toroids - less radio interference. In all cases buy decemnt ones. I got all my klit from Newey and Eyre and their oroids have been good, apart from one that kept tripping out that was buried inisnulation for wa while, but even when pulled out it did it, and it looked burnt, so I replaced it.

If you want, you can use a single transformer for several lamps, but each one needs a fat piece of 13A cable at least to feed it ..in general its easier to run 240V around and drop down locally for each lamp - there is little in it pricewise.

[Rafal]

Reason for the insulation is to get a bit of noise reduction from the flat above. Looks like 240V lamps are going to be easier all around.

Rafal

[N. Thornton]

Is it difficult to pull a couple of handfuls of insulation out and shove the transformer in? LV will give you lower running costs both in electricity and bulb prices.

Regards, NT

[Rafal]

There is some space between the ceiling and the insulation anyway so fitting a transformer is not the problem. Is the lack of space for heat to escape, I think.

Rafal

[Andrew Gabriel]

In which case the ceiling is a required fire break, and puncturing holes in it to fitting recessed lighting is going to compromise the fire break and would require the fitting of fire hoods over the lights.

[Rafal]

Hi Andrew

fire hoods? what are they?

[G&M]

If using toroids make sure they are reasonably well matched to the load. If the transformer can supply too much power the voltage will rise and blow bulbs on a regular basis.

[John Rumm]

These particular ones might be slight overkill for a domestic situation, but this should give the general idea:

[Zymurgy]

"Rafal" wrote

Glad it's just next door :-) - let me get my tape measure out ...

err ... 3.5 X 2.8 Metres X 2.4 high.

There's now 4 spot halogens in a line on a fitting. The fitting is 1m long and the (adjustable) spots are spaced at 25cm intervals.

Still dull in there !

Cheers

Paul.

[Andrew Gabriel]

They are required where you fit recessed lights into a ceiling, which is required to provide resistance to spread of fire, such as between flats.

Fire proofing between flats isn't really a domestic situation.

[The Natural Philosopher]

As long as there is a bit of air space you are OK.

The heat comes out via the plasteboiard into the room.

Its localises heat buildup that is the problem.

[The Natural Philosopher]

Or of reasonable quality. A transformer that drops volts under load is one that is wound on the limit of cost, and is one that runs hot.