LED Strip lights on LUL

[John]

Whilst standing on the platform at Moorgate waiting for a train I observed that the "strip light" tubes had "LED only" above them. Have LUL adopted LED tubes instead of fluorescent tubes?

[Chris J Dixon]

At a guess, because you get higher efficiency if you don't block some of the light produced by adding a filter.

Chris

[Andrew Gabriel]

Yes, in many places, for many reasons, but not everywhere.

Relamping cost is extremely high - much higher than the cost of tube or electricity. (Some of the tubes cost £5000 to replace, when you factor in all the planning, safety, access towers, etc.) It makes sense to spend a lot of money on high quality long-life tubes in such cases. Having said that, electricity consumption is also an important factor.

In the Underground, dust is a major problem, and tubes which emit their light downwards don't suffer from the lights dimming as dust settles mainly on the top. This becomes even more important when periods between relamping become very long.

There is also a move from the T12 740 halophosphate tubes the underground has used for years to retrofit T5 tubes. The T5 tubes are shorter and this enables the electronic control gear to fill the gap in the fitting. Fittings are rewired to remove the old control gear and feed mains supply to just one end of the fitting, which you will see is labeled "mains feed end" or similar, to remind the relampers that the retrofit ballast must be fitted at that end of the fitting. You can see these used where access for relamping is not so difficult (generally can be reached when standing on the floor or escalator).

The Underground has always attached a high importance to its lighting. It was the first installation of fluorescent tubes for lighting in the UK in the 1930's. Today, it uses one of the disused stations as a lighting research lab for evaluating new lighting schemes before choosing which to roll out across the network.

[Dave Liquorice]

Aren't "white" LEDs actually emit UV which is converted to the "white" light by phosphors. UV does funny things to dyes after a while.

[Andrew Gabriel]

Yes, but they're blue LEDs, not UV LEDs. The phosphor absorbs some of the blue, and re-emits it as longer wavelengths.

(UV LEDs are still incredibly expensive, and wouldn't be an advantage here as there would be higher Stokes loss in shifting UV to visible light than there is in shifting some blue to green/yellow/red light.)

[Grimly Curmudgeon]

Also this; A couple of months ago I mentioned the vile greenish tint from a so-called 'white' LED lamp. I stuck it in the back room and left it on every evening for the past several weeks. I noticed a couple of weeks ago it had definitely lost the nasty green tint and was slowly getting whiter. Progress continues...

[Grimly Curmudgeon]

Not kidding - I was chuffed to see fluoro replacements coming in, but at 28 quid a pop, no thanks.

[harryagain]

You can buy replacement LED tubes that go in fluorescent fittings. You chuck the old control gear away.

They cost around 10/foot