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Re: Replace fluorescent tubes every six months

Richard wrote:
Somewhere out there are some graphs of the decay in luminous flux over time;
at six months, IIRC, it's about half of what it was when new. But they
just fine. The culprit is cathode decay which causes less enerygy to be
transmitted through the mercuty vapour.

You can use them. They will work. But if you chnage them every six months
your plants will be much much happier.

This is not true for many lamps. Lumen maintenance is normally very good.
The ones to watch out for are wide spectrum plant lamps that are designed to
match the photopic response of plants. They do indeed fade fast but as I
said before they never come with any specs, so you can't estimate the lumen
maintenance. I just measured my 6 year old SPX 50s against new lamps and
they have not depreciated more than 20%. It is not fair to compare a brand
new lamp with an old lamp as lamps experience a great deal of lumen loss in
the first 100 hours. Here is a lumen maintenance curve for a 55 watt lamp:
This curve is nothing special. There are lamps that are much better than
this and lamps that are much worse. Here's another graph that is so crappy
you can barely read it:
http://dafnwebpd.mysylvania.com/IDMWEB/doccontent.asp?docid=003676784 It is
comparing 800, 700 and halophosphor lamps. Even the halophosphor lamps do
not fall below 80% lumen maintenance.