Trailing Edge Dimmer

[timsabre]

It may not be a fundamentally insoluble problem, however nobody has yet even come close to meeting theatrical requirements in a two-wire LED (or florry) yet.

- Not really a surprise, as Domestic/Office usage is pretty much solved and that is a much bigger market.

 

Not really, I have still yet to see a reliably dimmable 240V LED lamp, domestic or otherwise.

The main problem is that most wallplate dimmers are not well behaved at low settings with a small load. Of course as David A says you need to get some voltage there before anything is going to happen, and many wallplate dimmers are very flickery and unstable at the bottom end of the dimming.

 

As there's loads of electronics in these lamps, the most sensible way to go would be to replace your wall dimmer with some sort of powerline comms transmitter, and fit a receiver in the lamp. Then you just wire constant mains to the lamp send a control signal over the mains line. Nobody has done this yet either as far as I know.

[Tomo]

It may not be a fundamentally insoluble problem, however nobody has yet even come close to meeting theatrical requirements in a two-wire LED (or florry) yet.

- Not really a surprise, as Domestic/Office usage is pretty much solved and that is a much bigger market.

 

Not really, I have still yet to see a reliably dimmable 240V LED lamp, domestic or otherwise.

The main problem is that most wallplate dimmers are not well behaved at low settings with a small load.

That's what I mean.

 

Office/D0mestic usage rarely needs to dim below ~20%, so most 'wallplate' dimmers and lamps don't even try.

[musht]

 

As there's loads of electronics in these lamps, the most sensible way to go would be to replace your wall dimmer with some sort of powerline comms transmitter, and fit a receiver in the lamp. Then you just wire constant mains to the lamp send a control signal over the mains line. Nobody has done this yet either as far as I know.

 

Well X10 does sort of, thinking about it for the OP

 

http://www.gds.uk.com/gds-products/arcsystem

[timsabre]

Well X10 does sort of, thinking about it for the OP

http://www.gds.uk.co...ducts/arcsystem

 

Indeed, though X10 is not very common in the UK. Someone should do an X10 LED fixture.

The GDS thing is an interesting solution, hadn't seen that before.

[musht]

Well X10 does sort of, thinking about it for the OP

http://www.gds.uk.co...ducts/arcsystem

 

Indeed, though X10 is not very common in the UK. Someone should do an X10 LED fixture.

The GDS thing is an interesting solution, hadn't seen that before.

 

Sad thing is X10 was a UK invention, designed in Glenrothes, same design team did X11, the not so succesful Accutrak turntable.

 

Few RF automation controls appearing, LightwaveRF is available at Screwfix.

[David A]

There are now chips around which claim to dim LEDs down to 1% and which are controlled by a dimmed mains feed of most flavours. These are specifically designed for retrofit LED lamps.

 

Example.

 

I've got a step-up smpsu chip here on the bench which will start at just 0.9v.

 

This is not a plug in unit, there's lots of electronics, it's the plug in replacement "dimmable" LEDs that we were talking about.

[david.elsbury]

David, I'm not sure I follow your argument. The driver IC Brian linked to is specifically designed to go into LED replacement lamps and allow dimming down to 1%. Of course there's "lots of electronics", there needs to be, you can't just bung some LEDs across the mains waveform with a couple of capacitors and resistors and get fantastic results...

 

If you want a good quality replacement lamp then you need to pay for it, can't just buy an LED bulb from Poundland or wherever and expect great results.

 

I know your nickname on another online forum is "ledcynic", but I'd suggest you be careful of coming across as a troll here.

 

:)

David

[timsabre]

David, I'm not sure I follow your argument. The driver IC Brian linked to is specifically designed to go into LED replacement lamps and allow dimming down to 1%. Of course there's "lots of electronics", there needs to be, you can't just bung some LEDs across the mains waveform with a couple of capacitors and resistors and get fantastic results...

 

There are a lot of these "dimmable" driver chips appearing now, it's understandably a hot topic for IC manufacturers at the moment.

 

However there are 2 problems still to overcome in making a viable dimmable mains LED, the first is finding a dimmer which will reliably deliver 1% power to a load of 15 watts or so. In reality only the highest quality theatrical dimmers will do this.

The second is, your 1% power only comes along in a little spike every 10ms, and your driver chip has to keep going all the time. So you can't use the 1% power to actually light the LEDs because if you do then the power is gone and the driver shuts down again. Unless you fit massive capacitors, which there is no space for, you can't light the LEDs until a much higher dimmer setting. But, if you are fading down from full, some power remains in the capacitors and this allows it to remain lit at a lower dimmer setting. The result being you can snap the dimmer off at 10% but it won't come on again at the same dimmer setting, you have to turn it up before it will come on.

 

(If you haven't guessed, in my day job I am a Frustrated Mains LED Lamp Designer)

[boswell]

Update.

I tried 3 of the Viribright Par38 on an MK trailing edge dimmer, seemed to work OK but no noticeable difference to our ancient Green Ginger leading edge dimmer.

Located a Helvar DIGIDIM 454 which is a 4 channel trailing edge DMX dimmer (500w per channel) at £700 + Vat

 

Took the plunge and changed all our house light 100W Pars to Viribright 73488 warm white 18W Pars (25 units) and fed them off 2 circuits of our Green Gingers.

They have behaved perfectly since July 2013. In use every day by cleaners and performance so about 5hrs use 6 days per week.

Dimming curve is a bit lopsided with all the action taking place at the bottom end.

Also borrowed a Helvar DigiDim 454 trailing edge dimmer to try out. This also worked OK but was a sod to set up.

There was no noticeable difference in behavior between the Hevar & Green Ginger dimmers.

The Hevar had an inbuilt LED dimming curve which was more linear or we could use the Green Ginger and put the curve into our desk instead.

We chose the latter route and saved £700

 

Bulk buying 25 Viribright LED Pars got the price down to around £16.80 +vat each

 

HTH

[boswell]

Update

5 of the units lasted just on 14 months, another 4 have failed since and it's not 2 yrs yet. Distributor has disappeared and Viribright are not interested. so much for the 3 yr warranty.

Also, not found replacements at reasonable price. back to PAR38 80w. LEDs are not reliable enough yet!

 

 

 

[timsabre]

Some are, we've installed some Concord/Sylvania led fittings at my church, they have a great light quality and no failures at 3 yrs. They are a full fitting not a replacement lamp though. The trouble with lamps is getting decent cooling as there are so many different fittings.

[Don Allen]

Yes my question is what cooling is there for the Viribright Par38 as if they have gone into a halogen fitting, there may not be enough cooling for the led power supply ?