Fishkeeping - bulb spectrum confusion

wrote in message
ups.com...
I thought that 5000K or 5500K were the proper spectrum for plant tanks.
I've been checking out people's tanks online and they are using
spectrums from 6700K all the way to 9300K. Is there an optimum
spectrum? Right now I'm running a 27 watt 5500K and a 9 watt 5000K
bulbs on my 12 gallon.

You must be careful when talking lights, and don't confuse colour
temperature with spectrum ;)

5000K means the lights "temperature" in degrees kelvin and is only slightly
related to spectrum when talking discharge lights such as fluoro and halide.

Spectrum can be independent of colour temp. but related to another figure
you'll see around called CRI, or Colour Rendering Index. If the spectrum,
intensity and CRI are wrong then you could have an algae outbreak too,
because aquatic algae love green light, for instance, so research well
before you choose tubes.

All of these three things are important to aquarium plants and must be
right.

For spectrum you want the light emitting in the blue and red parts of the
spectrum predominently, with as little green in there as possible. The
Philips Aquarelle, NEC HD/G range and plant specific tubes at both hardware
stores and the LFS are in this spectrum.

The colour temp isn't super important IMO., but you should aim for about
5000K. The Philips Aquarelle I use is supposed to be 10,000K and emmits a
pink light, where you would think it's going to emit a blue light. I use
another tube which comes from China, which has it's spectrum data on the
side and that's only 4800K and is blue - so go and figure ;)

In Europe and particularly Holland, they go for plant spectrum, low colour
temp lights, as low as 3400K, which gives a look like an incandescant light
bulb on a dimmer, to my eyes at least - warm in a word.

The CRI is the figure that represents the colour rendering ability of the
tube in comparison to tropical mid-day sun light (5600K).

The figure is up to 100, so the Aquarelle at 89 and the Chinese no-name at
93 CRI are pretty damn close to sunlight as far as colour rendition of the
fish go, but mean jack to the plants which are using red and blue for long
and short growth respectively.

Here is a link to some great information about lighting for plants

http://www.csd.net/~cgadd/aqua/ah_main/mar1998.html

It's a complex subject, to be honest, and isn't as simple as degrees K I'm
afraid ;)

Oz

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My Aquatic web Blog is at http://members.optusnet.com.au/ivan.smith