Some points to consider by Dana Riddle
http://www.masla.com/reef/lightingbasics.html
Zooxanthellae have a minimal light requirement called the Compensation Point. This is the point at which the oxygen produced by photosynthesis is equal to the oxygen requirement of the zooxanthellae. If light intensity is too low, a zooxanthella will not produce enough oxygen to meet its respiratory requirements and probably will not use enough of the coral’s waste products to be of any use. So, an increased photo period (the amount of time that the lamps are on) will not make up for an insufficient amount of light. Bottom line: The amount of light must exceed the Compensation Point!
Zooxanthellae also have a maximum light level - this is called Saturation Point. Exceeding the Saturation Point is senseless, as increasing the amount of light will not enhance the rate of photosynthesis.
Just one last term - Photoinhibiton. Photoinhibiton is when there is so much light that the photosynthetic process begins to shut down. In essence, too much light is just as bad as too little, resulting in the same effects. There is some debate as to whether this actually happens in aquaria. My personal opinion is that it happens a great deal. Two examples: Try to get some of the pretty red calcareous algae (Peyssonnelia, for instance) to grow directly under a 400 watt metal halide lamp. Try the same with some of the "Mushroom Corals" (Discosoma species). The calcareous algae will die within a few days’ time; the Mushroom Coral will react in a negative fashion and will shrivel in an attempt to hide from the light and will often die
http://www.masla.com/reef/lightingbasics.html
Zooxanthellae have a minimal light requirement called the Compensation Point. This is the point at which the oxygen produced by photosynthesis is equal to the oxygen requirement of the zooxanthellae. If light intensity is too low, a zooxanthella will not produce enough oxygen to meet its respiratory requirements and probably will not use enough of the coral’s waste products to be of any use. So, an increased photo period (the amount of time that the lamps are on) will not make up for an insufficient amount of light. Bottom line: The amount of light must exceed the Compensation Point!
Zooxanthellae also have a maximum light level - this is called Saturation Point. Exceeding the Saturation Point is senseless, as increasing the amount of light will not enhance the rate of photosynthesis.
Just one last term - Photoinhibiton. Photoinhibiton is when there is so much light that the photosynthetic process begins to shut down. In essence, too much light is just as bad as too little, resulting in the same effects. There is some debate as to whether this actually happens in aquaria. My personal opinion is that it happens a great deal. Two examples: Try to get some of the pretty red calcareous algae (Peyssonnelia, for instance) to grow directly under a 400 watt metal halide lamp. Try the same with some of the "Mushroom Corals" (Discosoma species). The calcareous algae will die within a few days’ time; the Mushroom Coral will react in a negative fashion and will shrivel in an attempt to hide from the light and will often die
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