I usually leave them to EOL. when the pond starts going green i know the lamps failed. The one i pulled out the pump last year is in a similar condition branded Hozelock

The UV output of this must have been very little if any. I don't mind changing the lamps every 12 months as they are only a few quid each. Not from the aquatics suppliers mind, the prices they charge is outrageous! I've just noticed in this picture one of the electrodes is broken but that might have been due to it being thrown about a bit since removal as when I went down a few days ago I could see the faint blue glow from the top of the pump.

What causes it to go brown?

Probably the mercury...the 8 watts life are awful, i have tested them in most brands excluding osram so far and i am lucky to get more than 6-8 months out of them. Philips ive had probably 4 months from them new. GE hybec made about 8 month and rest varied

That life time is quite poor. Surely the only difference between these and a normal tube is that the germicidals have a different glass and no phosphor so you'd think the cathodes would be the same quality.

They probably make them poor cos they're a special tube

The fly killer tubes from Sylvania seem to last as well as the standard ones. The chippy up the street had 2 of the 8w Sylvanias and one lasted about 3 years 24/7. The eol one took the other out when it started flashing as it's series.

No phosphor - No getter - something that shouldn't be remains in the tube ?

These tend to fail due to solarization of the glass. The intense 253.7 and 185.1nm UVC radiation is normally absorbed by the phosphor, but in the case of clear lamps there is no protective barrier, and the glass decomposes. The cheap lamps made from quartz are especially susceptible to this. Better lamps of Philips, Sylvania and Osram use a precoat of Alon C inside the glass, about 5 nanometres thick, and this offers a tremendous increase in life. The lamps cost a little more but can maintain 50% of initial UVC output for up to 8000 hours, whereas the cheap lamps typically drop below 50% within 1000h.

By the way Oliver, don’t be deceived by the visual appearance of insect attraction lamps during life! These emit almost all of their radiation at 368 or 350nm and have a tiny amount of blue transmission from the discharge. The visible blue has no function in insect attraction and stays fairly constant during life. However the UV depreciates quickly. The 368nm lamps last only 1 year and the 350nm only around 6 months. You can of course continue burning them far longer but then they give practically no UV wavelengths and you might as well just switch them off and stop wasting electricity only to produce that useless blue glow with greatly reduced insect attraction! Longer life types are made but tend to be only for the flykilling OEMs. These are very expensive because they have a protective coating around every individual phosphor particle to shield them from solarization and poisoning by mercury adsorption.

Our mosquitoes over here happily fly to the light of ordinary 765....

I hate mosquitoes (who doesn't?) but they do like the high colour temp lamps that I tend to like. They love the clear merc in the garden light but the clever spiders build webs all around that light and get a good feast when I run it all night!

I hate every flying insect. If they dont fly into your ears its your eyes or your hair or you have those nasty little black thunderfly fuckers that were in between my neighbours double glazing if anyone remembers that pic (they had the panel replaced not long after). Or you get stung on the arse by a wasp for no reason. Have to be honest i prefer winter because of the bugs... and you sweat like a pig in the house but soon as you open a window you get 40000 mozzies, dragon flies, and other little flying waste of space things in.

I agree with you there. Any wasps come in my house and they get brayed.

@James One of the takeaways up the street has used standard tubes in their insect killer. They look about 3500k and they seem to be attracting the insects just fine surprisingly.

That why in the US yellow GLS and gold fluorescent tubes are used as Insect are blind to that color spectrum.