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Are B&Q Celcus Lights Dimmable or not?

Postby cardos1972 » Thu Oct 10, 2019 10:46 am

Hi We've bought a B&Q Celcus light which has 14 individual 45W halogen G9 bulbs with it. When switched on it produces heat and is also crazily bright. So we want to be able to dim it. We've had conflicting advice so i wanted to ask on a forum.
Normally a halogen G9 would be dimmable i'm told and if I replace the bulbs with Dimmable LED's it could in theory be dimmable however as it is with the currewnt bulbs I'm told it's not dimmable. Is this because there are 14 x 45W bulbs which would be too much?
What do we need to do to be able to dim this light fitting please?
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Postby Mr White » Thu Oct 10, 2019 7:02 pm

A G9 lamp is Tungsten halogen.
These lamps run at a high temperature for a reason, during normal operation tungsten (filament) particles are given off, but because they are surrounded by very hot gas (halogen) they get deposited back on the filament again. (This is an ongoing cycle) To make this work the running temperature is around 2,500 but this would melt normal glass, so to avoid this problem quartz is used instead.

So if you dim the lamps you also shorten their life.

That said it was quite common for people to dim the lamps anyway (Even though it does shorten their life) However, due to the sudden inrush of current most dimmer switches would soon fail, so the manufactures of dimmers down rated them by 50% when used on a halogen lamp, to cope.

As you have 14 x 45w lamps this equates to 630 watts, so you would need a dimmer of at least 1300 watts, but the highest rated normal dimmer is only 1000 watts.

You now have several choices.
Take out every other halogen lamp and get a 500w dimmer, or change all of the lamps to dimmable LED.
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Postby ericmark » Thu Oct 10, 2019 8:59 pm

G9 to start with needs a protecting glass as if the fail they can allow white hot bits of quartz to escape, and in theory the temperature of the quartz envelope is critical, two high and the tungsten melts, too low and the tungsten is deposited on the quartz instead of back on the tungsten, in practice you can dim them, but their life is reduced as a result.

LED's are current dependent devices, so either an electronic current limiter is used, or a basic resistor (DC) or capacitor (AC) to control the current. With the basic current control you get around 60 lumen per watt and the LED can be dimmed, with electronic current control the electronics auto correct and wave form clipping so they will not dim.

Also if the dimmer does not have a neutral, then some current must pass through the bulb even when switched off, with dimmer-able bulbs there is a drain to ensure a very small current will not light the bulbs.

However the G9 bulb is too small to incorporate this within the bulb, so with a G9 LED you often need a 4 uf capacitor across the supply to bulb so there is enough current flowing to work the electronics of the switch.

So there needs to be enough room in the lamp to take the 4 uf capacitor, only place I could find selling them local was CEF, marketed by Levante they do work, my wife has a 5 x 5W LED G9 lamp and once the capacitor was fitted it worked with an Energenie electronic light switch. Without the capacitor it would not switch off.
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