Dimmable LED tubes.

[Dave Plowman (News]

To save me searching everywhere, are there any standard size (4 & 5 ft) LED tubes that can be dimmed in the same way as an LED bulb, using an LED wall mounted dimmer? But must be warm white.

[Andy Burns]

I suppose 3000K isn't /that/ warm, but

[Brian Gaff (Sofa]

Well an engineer many moons ago told me that as tubes need to have a high voltage on them to get the initial strike then when the gas conducts you need a lower voltage to keep them going, dimming them is usually not possible Often the ones you use on stage etc, can be dimmed by changing the duty cycle of the peaks in voltage, but below a certain point a form of hysteresis comes in and the go out and you then need to raise the duty cycle and restart them. There may of course be special tubes or indeed work around, but the explanation seemed to be right to me having tried these ideas when I was young and foolish. Brian

[Max Demian]

These are /LED/ tubes.

[Animal]

I used to operate an installation of switchstart fluorescents on a variac dimmer. They dim fine down to a point, then they just go out. I'd guesstimate this is somewhere around 15% light output. The dim function was only used to fade the lighting up & down, so no real problem.

The issue with dimming them is that the electrodes sputter, reducing tube life heavily. There is also incompatibility between old triac dimmers and switchstart systems. Fluoresents can be dimmed without problem if power is fed to the filaments.

[NY]

I always wondered how it was possible to dim fluorescent tubes. With tungsten you can truncate the sine wave early or start it late on each half-cycle, and the filament averages out. But tubes need a minimum voltage to strike, and will flicker or go out.

I used to ponder this sometimes in school assembly when it was held in the lecture theatre that had banks of tubes on the ceiling and push-buttons for OFF and ON by the various entrance doors and on the lecturn. These dimmed the lights up or down over about 2 seconds, which was well impressive in the mid 1970s.

When I was in the 6th form I helped out with the lighting for a school play that was held in the lecture theatre. Most of the dimmers in 19" racks were for the tungsten theatrical lights but there was also a chest-freezer size cabinet which sounded like a swarm of angry wasps as the fluorescent house lights were dimmed; during dimming there was also the noise of a loud fan which kicked in to cool the triacs, so we were instructed to keep the door closed to prevent the noise being audible to the audience. They only ever staged one play in the lecture theatre, before going back to the old school hall with its wire-wound linear pots, because the LT was missing several things that are very important for a play: curtains, wings, and a means for actors to enter and leave without having to go outside through the fire doors or walk up and down the stairs alongside the tiered seats. Someone goofed when they kitted the LT with theatrical lights which could never be used for lighting a play because of the staging difficulties (*) caused by no wings.

(*) Whenever I hear the phrase "staging difficulties", I always think of that exam question in Educating Rita "Suggest how you would resolve the staging difficulties inherent in a production of Ibsen's Peer Gynt" to which Rita's answer was "Do it on the radio".

[Animal]

yes. Switchstarts produced a spike voltage way above what any tube needed to start, so they still struck even on far below mains voltage.

too low electrode temp is what normally causes extinguishing. Maintain electrod temp, either by heating them or by being prompt with the fade out and the lamps run most of the way down.

Flashing is normally caused by the switchstart starter not the tube. FWIW the older thermal starters avoided this.

When dimming up from nothing (on variacs) there was mains frequency flicker at low levels, but the process happened quickly enough that people didn't usually notice. Most of that place was pre-war equipment.

[Dave Plowman (News]

I already have dimmable florries as under cupboard lights in the kitchen. Osram HF electronic ballasts made for the job. Don't use a normal dimmer - simply a pot connected to the ballast, so required extra wiring to have the control same place as the other lights.

Reason I asked is one has failed - doesn't owe me as likely 30 years old. So probably a good time to change to LED - if I can get something as good. All the other lights in the kitchen are now LED.

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[Dave Plowman (News]

I've just fitted non dimming LED tubes in older fluorescent fittings, and they look more or less like the original tubes - even light along the length. I suppose you'd call them frosted. Which is what I want.

These Ledison ones appear to show them being a number of single LEDs packed side by side and visible as such - or rather two out of the three choices (by dimmer type) do. Anyone know what the type with works with an ordinary trailing edge LED dimmer looks like?

[Andy Burns]

You have a frosted option (the green band)

[Dave Plowman (News]

Couldn't see how to select that. I'll look again later.

Wonder why they are so much more expensive than non dimmable ones? Seems a greater differential than with bulbs.

[Andy Burns]

Because they're selling tube together with dimmer/driver?

[Dave Plowman (News]

No. The dimmer needed is a separate purchase. And looking at what they charge for the same dimmer TLC sell sort of explains it - they are simply high priced. Sadly not been able to find an alternative source for these dimmable LED tubes.

[Dave Plowman (News]

I ordered up the Ledison dimmable tubes I wanted over two weeks ago from their website. Paid by Paypal - and that was taken from my account. Total amount about £80 including quite pricey P&P. Not been delivered.

Never got an email acknowledgement of the order - except from PayPal. Have emailed them - no reply. Tried asking them via their online contact page. Tried phoning them - after hanging on for ages no one available to take the call so left a message. No reply to that either.

So I'll have to try and get a refund from PayPal. Sadly, can't find another supplier.

[Andy Burns]

Maybe ask on Twitter if they're still trading?

[Dave Plowman (News]

Not looking good - no posts from them on their twitter page this year.

[Dave Plowman (News]

I started a dispute with Paypal to get my money back. 3 weeks from ordering and paying and zero communication from Ledison. And no replies to my emails. Tried phoning twice - and hanging on - but no human available.

And had an email from them today - after Paypal contacted them. Asking if I still wanted the goods. Cynical me says a delaying tactic to get outside the Paypal window for claims.

[Dave Plowman (News]

Hmm. Just had another email saying they will be dispatched Monday. Hope so, since they seem to be the only supplier of what I want. But having started a PayPal dispute they'll have to be delivered before the time for that runs out.

[Dave Plowman (News]

They arrived this morning - after a month of faffing around.

What I thought I was buying was the equivalent of an LED bulb which could be dimmed using an ordinary LED compatible dimmer.

But they have come with an external "triac constant current dimming driver" unit each and no wiring diagram I can find on their site.

It also helps explain the high cost.

Think I can work out how the driver is connected, but if the mains input is connected to a normal LED compatible dimmer, will they dim?

Given the high price I don't want it to be my mistake if they blow up, or damage the V-Pro dimmer.

[Andy Burns]

I did say as much, but you didn't believe me ...