The saga continues.

[Dave Plowman (News]

Most will already be bored with my saga of wanting LED tubes to replace florries - but be dimmable.

Finally got them installed.

Initial impression OK - although the 12w one slightly brighter per inch or whatever than the 30w one. But just about acceptable.

Then fitted the V-Pro dimmer.

And the difference in output comes far more noticeable when dimmed. Way beyond the point of being just slightly annoying. As they are effectively used in one run. And the previous florries being just fine.

What is odd is I ordered a 180cm tube which says on their website 32w. As does the delivery note. And the website checked again today. But the supplied tube says 30w

I've emailed them yet again.

I suppose I could try increasing the drive current to the 30w tube (the

12w is on minimum) But am using the setting they recommended for the 32w tube.

[newshound]

Don't increase it too far. I blew a UV tube the other day by connecting it to the wrong driver.

[Dave Plowman (News]

My worries too. More so given how expensive these tubes were. I'm wondering if they have a consignment stuck somewhere on its way from China

- given three out of the four bits appear to be substitutes.

[Andy Burns]

dim the short one, rather than brighten the long one?

[Dave Plowman (News]

It's on the minimum current setting.

[Andy Burns]

shunt resistor to divide some of the current away from the tube?

[Brian Gaff (Sofa]

This sounds more like a quality control issue from the makers. Just what is the tolerance range for these lights? I bet its something like 10% or maybe even more, so it will show up as worse if certain duty cycle dimming is used. I can well recall having a pendent light which hat three ordinary bulbs in it of 60 watt, all from the same maker, but as you dimmed it one of them seemed to go dim before the other two. Its not a new thing. In a way I'm glad I cannot see these days, never have to worry about such odd things. Brian

[Robin]

I would not expect LED drivers with different outputs to respond to a triac dimmer with identical power curves. Did the retailer or manufacturer say they would?

I have no experience of other dimmers (DALI, 1-10 etc) but AIUI even they don't control directly the power to the lamp so can't guarantee that different drivers deliver exactly the same proportion of energy to different lamps.

[Dave Plowman (News]

If the two tubes - a 180cm 32w and a 90cm 12w were the same brightness on full, maybe. But they're not. All the tubes in the range quote the same Ln/w, so I'd expect them to have the same output per inch, or whatever, same as fluorescent tubes from the same maker and spec. Although not quite sure why the wattage given isn't directly proportional to the length.

I have other LEDs in the room. More conventional dimming bulbs. If I unscrew one out of 3 on the same dimmer, while dimmed, the others don't change their level.

But I'd be the first to admit I'm not an expert on LED drivers.

[Robin]

I may well have missed something but 12 W into a 90 cm tube seems likely to give the same output per unit length as 30 or W 32 into 180 cm only if 30 cm or more of each tube are unlit. Workings:

tube length (cm) 90 180 unlit length (cm) 29.9 29.9 lit length (cm) 60.1 150.1 power (W) 12 30 power/lit length (W/cm) 0.20 0.20

or

tube length (cm) 90 180 unlit length (cm) 36.0 36.0 lit length (cm) 54.0 144.0 power (W) 12 32 power/lit length (W/cm) 0.22 0.22

If these are bulbs with built-in drivers then that's a case of identical drivers responding to the dimmer - not different drivers.

[Dave Plowman (News]

There is a bigger proportion of unlit tube in the smaller size.

But I was going by the specs on their site. Which don't make sense either.

The 180cm tube says 32w on their site, as does the spec. But the one supplied says 30w on its stick on label.

The 90cm one says 12w on the site and on the tube - but 10w in the specs.

If you want to look, here's the site:-

If you click on the tube size, you'll get the another link to click on for its spec.

Surely it would be common sense to assume the internals of the tubes - the LEDs themselves - would be identical, except in number, regardless of length? In the same way as you'd expect the colour to match?

You've missed out 10w as the spec on their site says the 12w tube is. ;-) And the long tube saying 32w in the spec, but 30w on the tube. Gawd knows which are correct.

I'd guess I'm not the only one who would want different sized tubes to react to dimming the same? Like say backlighting in a sign? Or concealed ceiling lighting in a room? And so on?

The drivers are the other query. Those supplied not even listed on their site. Again, I'd say it unusual to supply a variable output unit when fixed are advertised. As the variable units are more expensive.

[Robin]

The tech specs show the 90 cm tube has 180 chips while the 180 cm has

468. That - like the power ratings - is not consistent with them having the same "internals" - in the sense of the same density of chips per cm.

I used what you gave. With 10 W it's even less plausible they have the same output per cm.

As a general rule I don't assume I'll get what I want, and certainly not at a price I can afford. If even dimming was essential I'd think in terms of multiples of identical lamps - or tapes - with identical drivers.

[Jacob Jones]

That problem is fixed by use the long led strips you cut to length.

[Dave Plowman (News]

I wanted the same sort of even light you get from a fluorescent. Not a multiple series of individual lights.

[Dave Plowman (News]

Ok. Are you saying it is normal to get the same type of tube from the same maker where the output per cm of the active part varies by a noticeable amount?

This has never been the case with new fluorescent tubes of the same spec in my experience. Or even the LED replacements for such I bought from TLC at a much lower price. Which are used in a similar way.

If you look at the specs on the TLC site, their figures don't scale either. But do subjectively match, as I'd expect.

I can accept different sizes might dim differently on the same dimmer, but doesn't make much sense to me either. But not per cm when used with no dimmer. If this was the case I'd expect them to say so on their site.

[Steve Walker]

They're close enough together that they'll appear as one, as long as you have a decent diffuser.

[Dave Plowman (News]

You mean like the tubes I've bought? ;-) I specifically wanted frosted. Why I never bothered even trying early LED tubes.

[Andy Burns]

I don't have this under my cupboards, but I do have it above the door across my porch

stick 60 LEDs/metre tape in it ...

[Robin]

I don't have enough experience to comment on what's normal. My point was only that the specs for these particular tubes suggest to me strongly that they might well not scale linearly (even leaving aside the different drivers).

That makes me wonder about LEDlite's figures. E.g. the 4 foot cool white is shown as 2200 lm and the 5 foot cool white as 3350 lm. I'd expect (even after allowing for the eye's non-linearity) 25% longer giving 50% more lumens to mean a subjectievly different perceived brightness.

I don't think I can usefully comment further on that.

[Dave Plowman (News]

I too wonder about their figures. Saying a tube is 32w, but the one supplied says 30w on it. The 12w one says 12w on it - but says 10w in the spec. And then there are the drivers - not listed on their site. Told they were substitutes. But not why. I'd guess variable output ones being more expensive than fixed - even more so when they are set at minimum current.

The tubes do look identical, though, apart from the different lengths. Half the tube is frosted - the other half looks to be a heatsink. Ends can be rotated for best results in a fitting. Look very nicely made.

I've found the details of the managing director and will write to him. The only one who replied to emails was the warehouse manager - who I doubt has much technical knowledge. And he hasn't replied to my query about the different levels. And the phone just says no-one available to take a call

- leave a message and we'll phone back. Which they don't.