I have been thinking about GDA vs. lighting for some time now. Consistently I have noticed that GDA grows where the light on the inside glass surfaces of the tank is the most intense. If no light were to strike the inside surface of the tank my impression is that no GDA would grow on the glass. That is obviously impossible, but it isn't impossible to greatly reduce the amount of light striking the glass.
Tom has noted that pendant MH lighted tanks have less GDA than PC lighted tanks. MH lights tend to have parabolic reflectors, and with the light source being very small, the reflectors tend to be nearly focused, to produce a near parallel beam of light entering the tank. If you have a hex tank, this should almost eliminate the GDA problem?
But, for those of us having the typical rectangular tanks a different approach seems justified. What if we used a single T6 lamp, at the focal point of a parabolic cylinder reflector? And, that reflector would be narrower than the width of the tank, so light spilling over the end would have less chance of hitting the glass. Why wouldn't this virtually eliminate GDA for rectangular tanks?
Of course a problem would be getting sufficient light from a single bulb to grow plants, but two bulbs, each with its own reflector would solve that problem. Here is a bulb that would work for a 4 foot long tank, typically 55 gallons, Maxum 5000 47" F54-T5HO Mini Bi-Pin, and would give about 2 watts per gallon.
Are there any commercial aquarium fixtures that work in this way, or any available reflectors?
Tom has noted that pendant MH lighted tanks have less GDA than PC lighted tanks. MH lights tend to have parabolic reflectors, and with the light source being very small, the reflectors tend to be nearly focused, to produce a near parallel beam of light entering the tank. If you have a hex tank, this should almost eliminate the GDA problem?
But, for those of us having the typical rectangular tanks a different approach seems justified. What if we used a single T6 lamp, at the focal point of a parabolic cylinder reflector? And, that reflector would be narrower than the width of the tank, so light spilling over the end would have less chance of hitting the glass. Why wouldn't this virtually eliminate GDA for rectangular tanks?
Of course a problem would be getting sufficient light from a single bulb to grow plants, but two bulbs, each with its own reflector would solve that problem. Here is a bulb that would work for a 4 foot long tank, typically 55 gallons, Maxum 5000 47" F54-T5HO Mini Bi-Pin, and would give about 2 watts per gallon.
Are there any commercial aquarium fixtures that work in this way, or any available reflectors?
