Arrgh! Fluorescent phosphor mix/ageing

[unopened]

I just replaced a Philips 120 cm 827 with an Osram, as the Philips was flickering badly, and replacing the ballast hadn't helped. Couldn't get a Philips near where I lived, and I doubt if anyone does 120 cm fluorescent tubes mail-order at any reasonable price, if at all.

I noticed that the spectrum emitted by the Osram was significantly different to the tube next to it - the Osram being of a more greenish cast (or the adjacent fitting more pinkish). (The tubes are adjacent to a white tiled splashback). I swore gently under my breath. So off I go to another room to extract what I thought was an existing Philips tube to swap, so I could get the same spectrum in fittings next to each other. This was working on the assumption that the phosphor mix between the Philips and the Osram 'Warn White' was sufficiently different to show up as different emission spectra.

Now here's the odd thing. The older tube had a spectrum that matched the older fitting in the kitchen - which was good news, but wasn't a Philips - but in fact another Osram. The older fitting has a Philips tube.

So, I'm lucky to get a colour match good enough for my eyes, but now intrigued: do fluorescent tube emission spectra change subtly over time as they age? It's the only explanation that makes sense to me.

It is also incredibly irritating. It looks like that if I have multiple fluorescent fixtures in a room, changing any one of the tubes will stand out like a sore thumb until it is 'run in'. Yet another irritation to deal with when using 'energy efficient' lighting.

Grump over.

Sid

[Andrew Gabriel]

They do, which is one reason why installations where this is critical are relamped altogether. However, Osram as a name has moved between several companies over the years, and it's more likely that the phosphor formulation isn't the same between the old and new tube.

827 designation doesn't guarantee the same spectrum.

[unopened]

While I'm being irritated, I'll grump again that there's nothing on the old tube or new tube (that I can see) that allows me so see of the phosphor formulations are the same. As you say, if it is critical, it looks like I'll have to replace all at once.

I haven't got around to replacing the fittings with dimmable high frequency ballasts and tubes with higher CRIs yet (as recommended to me in this group, possibly even by you). The flicker on the current fittings gets to me occasionally - noticeable in my peripheral vision, especially when I have a headache.

Thanks again.

Sid

[meow2222]

FWIW, if its just the flicker that bothers you, its possible to add a series capacitor to an existing ballast to turn it into a leading power factor ballast. Now, 2 fittings, one lead one lag, and you get a lot less flicker overall. And since you've still got a large inductace in circuit, its not affected by the issues ready made lead lag ballasts have.

BUT don't experiment, the cap value is somewhat critical, get it wrong and you'll have a problem. See Droppers on the wiki for more info.

NT

[unopened]

Thanks - doing that is beyond my current safe technical competence. I should also point out that the two fittings are not parallel, but end- to end under kitchen cupboards (total length 2.4 metres and a bit) so the technique wouldn't be applicable. I have heard of it before.

I found the message that pointed me towards high-frequency dimmable ballasts in here:

the uk.d-i-y discussion on "Options for flicker free lighting source?"

Regards,

Sid

[Andrew Gabriel]

I don't recall that, but maybe.

You generally have to relamp all tubes in a dimming installation at the same time, as their dimming characteristics change with age, and otherwise they will behave differently at lower lighting levels.

Also, when using new tubes on dimming ballasts, always run them at full power for first 100 hours.

[Dave Plowman (News)]

Yes. I work in TV and if fluorescent lighting is used in a location where it is the main lighting - like say in a walking through a corridor shot where you can't use extra production lighting - they are all replaced at the same time. A TV camera is more sensitive to colour temperature mismatch than the eye.