05-31-2006, 08:22 PM
Join Date: Mar 2004
Location: between Here and There
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Lighting for a planted tank should not be chosen on color temp alone. It is true that 'full spectrum' bulbs are referred to as bulbs between 5000 Kelvin (K) and 6500 K and are best for planted tanks. Yet this does not indicate what type of light (wavelength in nanometers) the bulb is actually emitting. If you want both good leaf development/growth (blue light) and stem elongation (red light), you need light in both the blue and red spectra for photosynthesis.
You need a mix of blue and red for your plants, and green for you (brightness as perceived by humans). If your lighting looks extremely bright and your plants seem ultra-green, it means that you have lighting that outputs strongly in the green spectrum. Do not equate this with good lighting for your plants, because plants don't use light in the green spectrum for photosynthesis.
For green plants the lighting peaks that are most important:
Red pigmented plants use more light in the blue area of the spectrum.
Beyond choosing lighting that is optimal for photosynthesis, as above, you should choose lighting with the color temperature that best suits the aesthetic goals of your tank. So, don't obsess about color temperature beyond how you want your tank to look. From a color temperature standpoint, blue-colored light will enhance blues in your fish. Green-colored light will make the tank look bright to humans and enhance the green color of your plants. Red-colored light will enhance the reds in your fish, and any red plants. If your lighting looks extremely bright and your plants seem ultra-green, it means that you have lighting that outputs strongly in the green spectrum.
I have attached some jpg's to help understand lighting and how plants react to it. I have found it best to provide a mix of lighting to a planted tank. The GroLux bulb is perhaps the best plant bulb available but it has very little green light so the visual effects of your tank will look dim and purplish. Yet if you add some other lighting such as a Philips 6500K the effect is more pleasing to the eye and still beneficial to the plants.
Last edited by Newt; 01-28-2008 at 04:16 PM..