Advice on bathroom lighting in shallow false ceiling

We're still mulling over ideas for the lighting in the refurbished bathroom at our flat.
The basic plan is now fairly well defined, six downlighters in a false ceiling which we will put up. The existing ceiling is quite high and is concrete or similar so making holes in that for downlighters is out.
How much light should one need in a 2.5 metre by 1.5 metre bathroom with virtually no outside light (it just has a narrow window onto a stairwell)? I guess the choices are 6 x 20 watt, 6 x 35 watt or 6 x 50 watt.
We're thinking of using MDF for the ceiling rather than plasterboard on the basis that it will be easier to work with and it might be more practical to make one or two panels removable for access. Does this sound like a good idea or not?
What's the minimum depth that downlighters need? I'm a bit worried about the heat in the (small) void between the downlighters and the real ceiling. I've no worries about the real ceiling being flammable as it's cement or something similar but what about the MDF and the battens used to hold it etc.?
Any comments on whether mains or low voltage downlighters would be better? A couple of them need to be IPx4 and I can't find many downlighters that quote the IP rating. In addition we'd like two matching (or at least similar) eyeball (i.e. swivelling) downlighters for above the washbasin.
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Chris Green ( snipped-for-privacy@x-1.net)

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snipped-for-privacy@isbd.co.uk wrote:

I'd go for 6x50W as the bulbs are a bit more robust.
300W spread over the area of the ceiling - 3.75 sq meters - is less than 100W/sq meter. That is about what my underfloor heating kicks out at full crack. If you are worried, use plasterboard rather than MDF. That will take a deal of heat. Or even Masterboard (multiboard) which is 'asbestos replacement' board
If you are worried about heat also, youi could run fat '50A' cable from a remote toroidal to the lights rather than tuck transformers up in the void. I'd avoid electronic transformers vbeacuse of the possibility of damp,. and the blasted buzzing they produce.
Use the special bathroom fitments where spalshing is likely.
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But do we actually need that much light in a 2.5 x 1.5 metre bathroom? Also I would have thought that low voltage 35 or 20 watt lamps would be pretty robust.

How easy is Masterboard (or Supalux) to work with? Is it similar to ordinary plasterboard, better, worse or what?

That's not really an option as there really is nowhere to put it.

Er yes, but what I'm after is matching plain downlighters and swivelling ones. I was hoping someone might be able to point me in the direction of a manufacturer/supplier who has matching ones with the required IP rating.
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snipped-for-privacy@isbd.co.uk wrote:

*shrug* I like teh 50W units. Nice and bright and tough. YMMV
I reckon that a square meter per 50W is about right.
About the right amount to heat a well insulated room as well :-)

Oh, its almost better - its a lot stronger than plasterboard - its gyspum filled with I think chopped glass strand. Think 'asbestos roof' and hats the sort of brittleness, tho its easier to cut with a padsaw etc.
Have to be a little carefil banging nails throough it - i'd drill and screw as per MDF, then fill the heads and paint.

They all look pretty much teh same - white,chrome or brass rim with or without eyeball. Screwfix must do em. I got cheapos from newey and eyre and they have been fine. I also used their individual toroids. Pretty good BUT they need air round em or the overheat and cut out. However they are hard to fit after the ceiling cos they are almost to wiode to pop through the holes. If I has to do what you are doing I might well add an access hole and use ne socking big transformer, and wire from that. 300W toroids are not that huge. AND it sounds like you have space above the new ceiling.
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fire
lord no. Halogen bulbs are around 2x as efficient as 240v filament bulbs: can you imagine 600w of filament bulbs in 4m2 of room? Using downlighting does kill the efficiecy tho, if you have anything but white/cream carpet, so 300w is probably a closer comparison. Still well OTT, unless youre filming in there.
I wouldnt recommend these downlighters myself. They're in vogue at the mo, but sooner or later will be uninstalled in large numbers due to their downsides. Its only a matter of time.
In most cases I'd put spots on the wall and point them up at the ceiling. Pick spots that you can put ordinary CFLs in. Better lighting, much more energy efficient, no glare.
Regards, NT
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Well the sample I've seen I quite like, though I don't in general like downlighters I think they do work quite well in bathrooms.

... and very unsuitable for a bathroom surely.
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snipped-for-privacy@isbd.co.uk wrote:

Nigel does seem to be quite *intense* in his opinions. Unlike his lighting solutions.
Go with what you like. I found most of this stuff doesn't illuminate wide areas well, hence use lots.
Fire risk taken care of by using plasterboard.
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snipped-for-privacy@isbd.co.uk writes

6?! Better budget on a pair of sunglasses then. We put 3 x 20w in our 2m x 2m bathroom and that is perfectly adequate.
By the way, as the lights are low voltage, fed using a proper (not electronic) transformer, and the bulbs are sealed, I didn't worry about IP4x ratings and stuck in "normal" eyeball fittings, including the one above the shower. We originally wanted (mains) wall lights but I couldn't find any IP rated ones in a design that I actually liked.
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OK, thanks, maybe 6 x 20 watts is the way to go then. Certainly my mother-in-law's bathroom which is a similar size is very adequate with six downlighters.

I have wondered about this and whether IPx4 rating is required when they are low voltage. I couldn't find any explicit information and, as the flat *might* be let again one day I need to keep to the letter of the (non-)law.
The other thing I'm finding difficult is that most downlighters seem to need a minimum of at least 4" void above them with many needing 6". Are there any that need less space behind them?
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