The categories basically boil down to this:
If you want to grow plants, you want a bulb that puts off high
Photosynthetic Active Radiation (refered to now as PAR).
If you just want to illuminate your tank without the radiation (unplanted
but want it to appear brite), you want low PAR.
But how are they different when you're standing there-in-the shelf of the
local home improvement store?
What is radiation when discussing light bulbs? This is a lot of the "heat"
you feel coming off an incandescent bulb. Yeap, it's not really heat as you
think of it, like "this room is hot"... Try putting a fan on the light
fixture and putting your hand under it again with the fan running... It's
still hot, but all the heat should have been blown away, right?
Depending on the "temperature" or "color" of the light, a plant is able or
unable to use the radiation. That is to say the "color" or "temp" where the
peaks of colors are in a spectrogram for a given light source (a spectrogram
being that rainbow colored pointed graph thingie you see on some packaging).
Plants don't see the whole spectrum like us... If they had eyes like ours,
they would see mainly yellow and red, and even infared which we can't see.
So... They're looking for radiation with a yellow or red color, which they
use to excite cholorphyll and manufacture sugars to "eat". But those light
colors look like crap to our full spectrum eyes.
Lumens is the overall brightness, no matter the "color" or "temperature".
And herein lies the trick to understanding this...
You're illuminating a device that has an output of energy (measured in
watts). It has each of these properties we've discussed. However...
The spiral bulbs are what we consider "high efficiency" bulbs are forced to
emit a more blue color, which requires more energy to emit (different gasses
to illuminate), BUT, emits very little "lost energy" as radiation that we
can't see (infared to red). This is where they get away saying they're
"saving energy" but really, they're not doing much of anything except giving
a more effective output of the energy input.
They can have the same luminosity as a "less efficient" bulb, but (and this
is of note) offer absolutely nothing to photosynthetic organisms. That's
why the spirals work great over fish tanks, as they have very little PAR to
offer to algae, but don't expect much of them for plants.
What has me jazzed about the Reveal bulbs is that they emit a very strong
peak in the yellows and reds, yet have been adjusted to also offer peaks in
the other colors, so it also looks good to my eyes.
Another way to look-in-it, and this is also why your deeper water
photography looks blue... The blue wavelengths were the only light waves
that had enough energy to penetrate that deep. Think of the blue waves of
light as long distance runners. Ready, steady, but wouldn't knock you over
if they ran into you. However, they could get back up, and keep going after
On the other hand, a yellow or red wave of light is like a sprinter. Tons
of energy right now, but not much endurance-in-all. They could plow you
over, but after the collision, they're not going to run much further, and
definately not-in-the rate they were going before they hit you.
Well, that's some thoughts. Hope that helps if you're considering getting
away from standard output flourescents.
The You Light Up My Life Madness, Toledo, OH
It's never too late to have a happy childhood.
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