by ericmark »
Thu Jan 30, 2020 12:14 am
The whole idea of the quartz is it gets that hot the tungsten of the filament will not deposit its self on the envelope but will return back to the filament, over time the filament thickness becomes uneven and it will fail, one hopes is simply fails, but some time one gets ionisation (bright flash) when heavy current can flow, it is hoped there is over load protection to protect the extra low voltage power supply when this happens.
So quartz lamps in theory should not be dimmed, the whole idea of the electronic power supply is to ensure a steady 12 volt to extend bulb life, both under and over voltage will reduce bulb life, I know we do dim quartz lamps, this is why the quartz goes black, but it is still bad practice.
Second is the electronic transformer must match the lamp, so a 20 - 60 VA transformer is OK for both a 35 watt and 50 watt lamp but not a 10 watt or a 75 watt.
The electronic transformer uses capacitors, what it actually does is turn the AC to DC charge a capacitor, turn it back into high frequency AC which allows the use of a very much smaller transformer and monitor the output and alter the mark/space ratio of the input to regulate the output voltage, the capacitors have a limited life, be it the power supply for a lap top or a set of lights it does have a limited life.
You can also get toroidal transformers these do not regulate the voltage, cost more, and could in theory last for ever, the idea of extra low voltage is the filament is thicker so lasts longer, and with toroidal transformers the output is a fixed % of the input, however they tend to have an inrush on switch on, so will not work with most dimming switches.
There is no problem dimming tungsten bulbs, and you can get 12 volt tungsten bulbs which do not use quartz, so no reason why you should not get a 12 volt power supply that can be dimmed, it is only a problem when used with quartz.
The toroidal transformer will work will LED bulbs just as well as tungsten, there is no lower limit and output frequency is same as input 50 Hz, many LED bulbs are marked 50 Hz, this may be a way of saying don't use with an electronic transformer as there is a lower output limit, however you can get electronic transformers which will go down to zero today, however it may be because it can become a transmitter, many electronic transformers state a limit of 1 meter of extra low voltage cable, this is so they will not become a radio transmitter. Since my house all toroidal transformers I have no problem using 12 volt LED G5.3 MR16 equivalent bulbs (Not MR16 as MR stands for multifaceted reflector and most LED don't have a reflector so just compatible) the 16 is 16 1/8ths of an inch across from the days of old ******* cameras.
In the many better to move to GU10 there are three flavours of the bulb, the GZ10 has a special reflector to allow the heat not to be reflected, only the light is reflected, (Dichroic reflector) which would make your ceiling hot, the GU10 has a reflector which also reflects heat and there is a small tapper so you can fit GU10 in a GZ10 holder but not a GZ10 in a GU10 holder, then we also have the L1 version with a pimple in the middle so only energy saving bulbs can be used, unfortunately many LED GU10's don't have the dimple so will not fit in the L1 (Taken from building regulation that required them) holder.
But with non L1 versions of the GU10 most bulbs with fit be it quartz, cold cathode or LED.
The problem is since 1966 it has been a requirement in the UK to take an earth to a low voltage light, even if the light does not require it, and many 12 volt lights were wired without an earth, so in theory you should use three core cable, even when earth not used.
I do have spot lights, but I did not fit them, except for above bed head where they allow me to read in bed, there are some advantaged with spots, it allows one to direct light into otherwise dark corners, but they are not very efficient, with tungsten 2" is small, but with LED there are cooling fins so not even 2" so very poor spread of light, aim at white ceiling and you realise they do have the lumen stated, but aim at a dark floor and the floor absorbs the energy, so you actually turn the light into heat.
I like many more fitted them when they first came out as considered them cool, even though in real terms they were far too hot, then regretted fitting them.
I would say there are a lot better lights out there now, unless your lighting a picture on the wall or using as reading lights. However we tend to be stuck with the holes.
And yes the electronic transformer often does have a auto protection system, and bulb too big or too small it will auto shut down, with a dimmer if dimming 50% then a 50W bulb is only 25W so a 35 VA electronic transformer will close down. Also not all electronic transformers can be dimmed, and of course the dimmer switch can also over heat and close down, and if the dimmer does not have a neutral these also have a minimum output.
I use neutral less electronic switches, simple on/off not dimming, but any power cut they auto switch off, electronic switches that use a neutral are far better, but in the main we don't have neutrals at the switches.
