I just installed a 400w MH in my hood.The flourescent tubes in the hood are only about 5 or 6 inches from the MH bulb.Is there any problem in having the tubes so close to the MH (heat). The end caps are not near the MH just the center of the flourescent tubes.
The heat will effect the fluorescents. The vapor pressure of the mercury in the lamp will rise with the rise in temperature. the arc will not produce the proper frequency of UV light. the target is UV with a wavelength of 253.7 NM. This shift in UV frequency will effect the exitation of the phospors on the wall of the lamp. A fluorescent lamp is designed for optimum performance with a bulb wall temperature of 100F. Your MH lamps have a MUCH higher operating temp, which varies depending on the MH lamp. Higher temps in fluorescents also alter the electrical characteristics which may allow more current to flow through the lamp. This may make the lamp look just as bright but it will effect the lumen maitenance and the lamp life.
Here is a plus, If you have VHO lamps you may have less of a problem. Testing has indicated that these lamps suffer less from temperature.
you loose 1% for every 2 degrees the ambient temp varies from 77F(the bulb wall is at 100F when the ambient is at 77F)
Some phosphors suffer from a color shift when subjected to higher temps.
thank you for your time and have a good day
PS This is why I disagree with the statement that fluorescents are as efficient as MH in Aquarium use. In the lab they test well, In our tight spaces they suffer from elevated temps. MH operate at such a high temp that the ambient temp is insignificant.
I'm so skeptical, I can hardly believe it!
joez: I have seen some companies add cooling fans which may reduce the effects, but yes I think fluorescents are operating less then optimal. I like the MH for its ability to resist temperature effects, and its smaller size.
I guess I did not answer Dale D's question; I do not think the fluorescents will break, they will just not run at peak effeciency and may burn out sooner.
This is my general opinion on lighting:
there is more to be gained by the reflector/lens of the fixture then the light source. The lamp is important because it will determine the color of light. How the light is focused at the tank is a huge factor for the intensity. In my profession the parabolic lens is becoming very popular because people are starting to realize the importance of putting the light where it is needed. I feel the same thing applies to the reef tank.