Possible Lighting Problem

[Charles Middleton]

Hi,

In my kitchen I have just in the process of installing four recessed eye ball down lights. These are the mains GU10 type. They are laid out in a square box shape with each fixture on a corner if you see what I mean.

Anyway, after looking at the instructions for the fittings it states the minimum distance for any object *in front* of the light before I presume the heat could cause a fire. This is fine as they are mounted in the ceiling.

However, one hole is reasonable close, I would say 10 to 15 cm to a copper pipe and some mains cable that runs through the ceiling void. So I put that fixture in and ran it for around 5 minutes, I then removed it, shut off the power and had a feel around in the hole to see if anything was heating up and it wasnt. I then repeated the process up to 30 minutes running time and the cables and pipe didnt feel warm at all.

So is the opinion on this that the fixture will be safe or am I running the risk of setting my ceiling void on fire and burning down my house. I guess the question is can dangerous levels of hear occur behind the fixture and is there a safe distance or a minimum amount of void that these things should be mounted in.

Thanks for the on going help.

CM.

[Martin Angove]

[...]

I just bought a few GU/GZ10 fittings (simple recessed types, not eyeball) and although I haven't fitted the things yet, I'm sure the instructions contain details about clearance around the recessed part. From memory, they are not to be covered with insulation, and at least

50mm (i.e. 5 cm) from any potentially flammable surface so I would have thought that 100mm or 150mm would be fine, but check the instructions in case the advice is different for yours. In any case I would expect the copper pipe to be ok - even were it carrying gas, there's no air in the pipe to let it burn, and copper is such a good conductor of heat that the point temperature is likely to be lower than you expect. PVC insulation on cabling doesn't like heat at all (normal PVC is only rated up to 70C, though it won't actually "melt" at that temperature) so keep the cable as far away as possible.

It is important however to realise the difference between GU10 and GZ10 laps which otherwise look similar and will fit the same connector bases. One (GU10?) is dichroic and the other is a simple reflector. A simple reflector reflects almost everything, including the heat, forwards. A dichroic reflector allows much of the heat (infra red) radiation

*through* the reflector so that the area in front of the lamp is comparatively cooler than an ordinary reflector. Of course, this means that the area behind a dichroic lamp can get warmer than that behind a simple reflector, though if the lamp is mounted vertically pointing downwards you are unlikely to notice much difference after it has been on a while.

FWIW, had I not been replacing the ceilings anyway, I would have cleared the 70 years of dust and detritus away from the recessed parts of my fittings, probably using a vaccuum cleaner, before turning them on.

Hwyl!

M.

[Andrew Gabriel]

They don't have same bases -- full reflector base has a bevel round the bottom which stops dichroic lamps being fitted. Substituting the other way round is OK. This is specifically to stop a dichroic lamp being used in a fitting not designed to take the heat it dumps backwards.

[Martin Angove]

Ok, I stand corrected. The point was valid though as many fittings are designed for use with either, and the user may not be aware of the extra problems with rearward heat build-up when installed in a confined space.

Hwyl!

M.

[Charles Middleton]

Had another look at the instructions and nothing mentioned about the heat from the top of the units. Ive done some more tests today and they seem to be fine and there is no excess heat build up in the ceiling.

Thanks for the info on that - I wasn't aware of that.

CM.

[Martin Angove]

I've just found the instruction leaflet for mine - Aurora downlighters from Screwfix (p163, 19324). The dimensions given are 135mm height - i.e. in total from ceiling to nearest obstacle above, and 75mm *from spring mount* to nearest vertical obstacle. The diagram shows a lamp almost completely enclosed in a box of these dimensions though :-)

Hwyl!

M.