GU10 LED lamps

[paulears]

I've just noticed our electrical contractor fitting small GU10 240V led lamps into some fittings - like these

 

They seemat about a fiver, to offer a really good cost saving on the tungsten ones, which seem to fail regularly. Do they dim?

Paul

[Gareth A]

Not sure if they dim or not. But I know from seeing some in use, they are quite dim to start with. Theres some in the arts centre I was refurbing a while back and they were meant to be ultra bright white ones, but they were more like ultra dim blue ones. As they were meant to be lighting pictures they werequickly removed for good. Though they did light up the heat sensor nicely.

[thelxbloke]

We've got some that contain R,G&B LEDs that automatically mix, these don't like dimmers for sure, found that out by accident on a staircase in a club, two dimmers on full, one each side of the stairs, once metered to see what was up, one was 230v AC the other was 100v.

 

Would love to know if the static ones dim though!

 

Chears

 

Steve

[Tomo]

It's almost certain that they do NOT dim.

 

Dimming LEDs is not anywhere near as simple as dimming a tungsten lamp.

 

You cannot reduce the voltage across them, as there is a very small window less than 0.5v wide in which they operate at all (too high - poof!, too low - nothing)

 

The realistic way to dim LEDs is through current control, usually via some form of pulse-width modulation. I run at 20 - 25kHz as it makes it less likely to cause audible interference, but any higher and switching losses start to pile up.

 

There are a few dimmable mains-voltage LED units, but they use some very clever electronics to detect the level they are currently dimmed to and fiddle a suitable PWM drive. Very clever stuff, and very expensive!

[james jag]

LED's work on a constant current system, I have fitted loads of low volatage eg, 48volts systems that are dimmable, but they are not cheap and the other thing that I have found with static mains gu10 is that the colour does vairy form one product to another, so it you buy some get a load of spares that are the same make :)

[AndrewR]

We have ordered some MR16 12v versions, (not sure of the brand) twice we have been sent them back, as the ones we recieved only had 2 functioning leds. Not ordered any more. Anyone else had the same problem?

[Guest lightnix]

DMX controlled LED dimmers are beginning to appear, although at the moment they are few, far between and expensive (although this will change very soon, I expect).

 

Expect a drop in intensity - all the 50mm diameter LED lamps I've seen, which use 5mm LED clusters, give light output roughly equivalent to a 15-20W halogen e/quivalent, although you can double, even treble, the number of lights and still save on power.

 

There are a number of LED bulbs beginning to appear on the market now and, as usual, it's a case of getting what you pay for and at a fiver, I have to say I'm suspicious.

 

Pretty well all white LEDs (other than Luxeons) have some kind of blueness towards the centre, how much is a quick indication of the quality of the LEDs. White LEDs are actually blue LEDs, with the chip coated in a phosphor layer which absorbs some of the blue light and re-emits it in the yellow portion of the visible spectrum; the combimation is perceived as white. The blue centre is caused by the welding of the microscopic wire from the leg of the LED onto the chip. In posh, expensive LEDs, the welding in done using state-of-the-art equipment, which only leaves the tiniest of spots; in cheaper LEDs, the welding can be a more ham-fisted affair.

 

Then there's the binning codes to consider. When a batch of white LEDs are produced, their quailty and consistency varies across the batch. The output of the LEDs is then tested and they are sorted and coded (or "binned") according to the results. The best LEDs, with the purest white and brightest output will be given a "high" bin code; those which are a bit off-colour and / or slightly dim will be given "lower" codes. When product manufacturers select LEDs for their products, they have a choice of producing a top-notch one, using high-bin LEDs, or a cheaper one using low-bin. The cheapest products tend to use the "bargain bin" (my terminology) - LEDs which work, but were so far out-of-spec, they may not have even merited a "real" bin code; the result is poor colour / intensity consistency between individual LEDs and individual bulbs. You can find out more about binning and codes on the various LED manufacturers websites.

[Andrew C]

as the ones we received only had 2 functioning leds. Not ordered any more. Anyone else had the same problem?

I bought one to try, and stuck it in one of three holders on a circuit in my kitchen on its own. Just as you describe, two LEDs lit up. After a bit of cursing, I realised that the load on the transformer was WAY too low. By sticking 35W lamps in the other holders, the TX started kicking out 12V and all was well. Except the beam "angle" and colour...

[back_ache]

dim or not

I've noticed that in an advert for stand varible waveform dimmers they can dim most led loads they also say in the advert that normal switching dimmers can't.

live design online artical

[niclights]

I have considered these before, but the brightness concerned me as Lightnix points out.

 

For those that have fitted GU10's or GU5.3's, how have you found the light output? Are they being used to illuminate a public area or just for highlighting? Last time I looked into doing this I spoke to manufacturers who (rather surprisingly) admitted they were not yet suitable for replacing 50W halogens, even the 5W luxeon jobs. By my calculations they were not an economic option on paper, but I do like the idea of not having to replace or worry about blown lamps. Also I would obviously like to do my bit for the environment. (just as I do with all those pars.... :) )

[Tomo]

LED's work on a constant current system [snip]

Not true.

 

There are two ways to dim an LED:

Variable voltage over the tiny range available. This is simply not used, because control is extremely difficult and the LEDs must be matched extremely accurately.

 

Variable current - this is what is usually used.

Dimmable modules usually contain a DC-DC converter that fixes the voltage across the LEDs, and as a consequence varies the current according to the applied supply voltage.

 

Sine-wave dimmers work because they effectively apply a PWM load to the LEDs - the rectifier/LED driver in the LED module fails at low voltages, and by varying the height of the applied sine wave the time per cycle where the LED fails to light changes, causing dimming.

 

As to the expense of dedicated LED dimmers:

If the dimmer recieves DC hard power and a control signal, then they are very cheap - the expensive bit is the AC-DC inverter.

 

I have one on my desk that is rated up to 24Vdc at 20A (48Vdc with a better heatsink, wouldn't want to go higher for safety reasons), and the total component cost was around £10 for a one-off on copper stripboard.

Go to one-time-programmable surface-mount, and the unit cost drops to around £2.

 

This module could happily drive an array of 100 x 20 lumen Luxeons from a pair of 12v car batteries.

[mattwright15]

I have fitted these LED GU10 lamps into my bed room and promptly replaced them with tungsten lamps. with all 8 on I think my mag lite out powered them by twice fold. I wouldn't recommend at all fitting them into anything unless light out put isn't the issue and current draw is.

[Yorkie]

I've got a GU10 desk light that's expensive to maintain; if knocked sharply by accident when it's on, the lamp fails. Its running temperature is annoyingly high too (and the switch is behind the lamp socket!).

 

Whilst I don't really expect any more from a £10 quick buy from Argos, I may well try one of these lamps to see if it helps - certainly running remperature and knock-resistance should be improved.

[LDODD]

For those that have fitted GU10's or GU5.3's, how have you found the light output?

 

 

We are now at about 35W Halogen in like-for like output.

 

Unfortunately, we cannot actually compare exact like-for-like output as it's not simply a case of getting out the light meter (actual comparison data is being worked on).

 

We use alot of replacement lamps, but no those actually shown above. Cree and Luxeon LED's are a must for any serious application, where actual light output is required!

I would avoid the 5mm LED (in clusters) lamps. We have had major reliability and binning issues. check out the Luxeon website for certified manufacturers - These are companies who have invested time and resource into process and will offer guarantee on binning and life etc.

 

Successful dimming tends to be done using PWM via DMX. There are some 0-10V interface products that I've used which have fallen over because of the discussed reasons.

 

We are working on "Mains Dimmable" replacement units at the moment, using some clever voodoo electronics. Cost will be an issue for the foreseeable, but I will post here when we have something for you guys to test/play with/destroy etc.

[niclights]

Tnx for that. I understand that direct comparisons are very difficult. The applications that interested me are non-dimmable GU5.3/10 that provide all the illumination for public thorofares. I was aware that the luxeons were the only realistic option and a 35W equivalent may now be getting close, but cost is still hard to justify.

 

Recently I have been reading about the latest 10W cluster units announced by Pacer. These look impressive - especially their max current-handling and retinal damage capabilities! Will you be looking at utilising these in the near future?