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Re: [APD] Plants not pearling, growing slowly

Unlike some people, all light bulbs get dimmer with age
("age" mean time illuminated). But it's the change in the
slope of the curve for fluorescents that can fool one. As
much as 20% of the brightness can deteriorate in the first
few months -- the curve starts out very steep. So a new
bulb will seem much brighter than a nearly new one -- say
two bulbs a couple of months apart in age and used 12 hours
per day. But before too long the diff will be imperceptible
-- the curve becomes more gradual until it's nearly but
never really horizontal.

Halophosphors (that icky office lighting) deteriorate more
rapidly than do the rare earth phosphors in "broad
spectrum" and "tri-phosphor" bulbs.

--- Jerry Baker <jerry at bakerweb_biz> wrote:

> S. Hieber wrote:
> > It's several years until you get down to half output.
> The
> > decline is very rapid at first and becomes more gradual
> > over time. So a new bulb will seem much brighter than
> say,
> > one that is a month old, but one that's a few months
> old
> > won't seem (and won't be) a lot dimmer than one a year
> or
> > two old.
> I've never kept aquarium bulbs long enough to really see
> this, but using 
> the compact fluorescents I have around the house as a
> reference. 
> Sometimes over a period of about 3 - 5 years a bulb gets
> so dim that 
> when it is replaced, it seems as though the light in the
> room has 
> increased by three times or more. I'm used to eyeballing
> light levels 
> for photography, so I'm used to thinking of light in
> terms of stops 
> (doubling). Maybe that's not helping here.

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