Dimmable spotlights

Paul_Thomas · 6 Oct 2007

I have a number of ceiling spotlights around the house, some are labelled as dimable and some aren't.

What makes a spotlight dimable?

And can non-dimable ones be upgraded?

RF Lighting · 6 Oct 2007

Usually the type of transformer on ELV downlights is what makes the difference, and yes you can normally swap a non dimmable Tx for a dimmable one

Paul_Thomas · 6 Oct 2007

I have recentl purchased a couple of sets of mains voltage dimable spots, don't look any different to the others I have.

One cheap set I have in the kitchen (not sold as dimable) do not work at all well with a dimmer switch. They dim slightly then flicker and go off if you turn them down too much.

Steve · 6 Oct 2007

As RF said it depends on the transformer. What more can we say? They have different electronics.

Paul_Thomas · 7 Oct 2007

Surely mains voltage dimable spots don't have transformers?

breezer · 7 Oct 2007

who said they were mains?

salem2000 · 7 Oct 2007

breezer said:
who said they were mains?

Who said they have transformers?

breezer · 7 Oct 2007

salem2000 said:
Who said they have transformers?

they have to have transformers, since the op said

Paul_Thomas said:
............some are labelled as dimable and some aren't.

salem2000 · 7 Oct 2007

breezer said:
salem2000 said:

Who said they have transformers?

Click to expand...

they have to have transformers, since the op said

Paul_Thomas said:

............some are labelled as dimable and some aren't.

Click to expand...

Normally I would agree, however I have two downlight's in my porch which are mains and labeled "not dimmable" because they had these supplied.

Obviously we know they can be changed for standard GU10s, and would thereafter be dimmable, but that would be contrary to manufactures instructions.

breezer · 7 Oct 2007

yes you are quite right, some thing i had overlooked, compact cfl's

GaryMo · 7 Oct 2007

breezer said:
who said they were mains?

The OP?

Paul_Thomas said:
I have recentl purchased a couple of sets of mains voltage dimable spots, don't look any different to the others I have.

One cheap set I have in the kitchen (not sold as dimable) do not work at all well with a dimmer switch. They dim slightly then flicker and go off if you turn them down too much.

Steve · 7 Oct 2007

The OP doesn't seem to know what advice he wants.

Paul_Thomas · 7 Oct 2007

Steve said:
The OP doesn't seem to know what advice he wants.

Thanks.........

The advice I want is to understand why some GU10 spotlights are sold as dimable and some aren't?

I have some CFL's which obviously aren't dimable, I have some 'cheap' GU10's which don't say that they are or aren't dimable and they don't work properly with my dimming switches and I have some new GU10's which state that they are dimable.

So what makes some dimable and some not? (Is it the cheap GU10 bulbs, or perhaps some circuitry in the connecting units that the bulbs plug into)

Space cat · 7 Oct 2007

There are two or three parts to consider in a dimmable lighting set-up: the dimmer, the transformer (for low voltage lamps only) and the lamp itself.

Unless it says otherwise, a dimmer is suitable for standard mains voltage bulbs only. No transformers and no fluorescents. You can use it for mains halogens but you shouldn't (see later). A dimmer has a maximum power rating and, in most cases, a minimum rating. If that's got you puzzled it's because of the way triacs work.

Unless it says otherwise, a transformer is not suitable for dimming. Most of the things sold as transformers aren't transformers at all; they're switch mode power supplies. Real transformers can be dimmed - but only if the dimmer says so.

Unless it says otherwise, a fluorescent light is not suitable for dimming. The starter circuit won't work properly.

Although a halogen bulb can be dimmed you shouldn't do it. Their filaments run hotter than standard bulbs so tungsten boils off faster and lands on the envelope. The purpose of the halogen is to collect this tungsten and return it to the filament. It's a clever trick but the envelope has to be extremely hot to make it work. If you run a halogen too dim for too long, tungsten will build up on the envelope and the halogen will remove it from the cooler parts of the filament instead. The first problem can be reversed by turning up the brightness; the second is permanent.

Paul_Thomas · 7 Oct 2007

Thanks Space Cat for a very thorough reply, so even the dimable spots I have purchased will not be ideal for the job.

I have a 400w dimmer switch running 5 x GU10 (50w) spots but it doesn't work properly. This is why I posted the first question, these were particularly cheap and cheerful set and included the bulbs. (10 spots + bulbs for £20!)
I was wondering if just changing the bulbs would sort the problem, or whether there was something built into the fitments.

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Dimmable spotlights

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