As for the original question - no, raising the light is not a viable method for reducing the light intensity in the tank if he is using a decent reflector. layers of window screen are much more effective.
Lets consider the light hitting the water surface in two parts - the light coming directly from the bulb, and the light hitting the water surface after bouncing off the reflector.
For the reflector light - since the light hits the water surface at close to 90 degrees, there is almost no spreading, so no real effect of height above water on light intensity enterring the tank. And we both agree that the reflector contributes more than half the total light penetrating the water surface, right?
For the light hitting the water surface directly from the bulb, the "lost photons" are those that hit the water surface at a flat-enough angle so that much of them are reflected by the surface rather than refracted into the water. This angle is unaffected by the height of the bulb. So, unless you raise the bulb really high (high enough that even the photons from the bulb that are coming down at high angle to the water surface would still miss the tank), you will have the same percentage of reflected versus refracted photons. And, if you have a hood around the top of your tank (instead of free-hanging pendants), some of the light that "missed" the tank because you had the bulbs mounted high will still bounce off the sides of the hood and hit the water. The only lost photons (lost energy) are the ones that hit the water at too shallow an angle to penetrate.
You mention ripple effect, and yes, ripples do have some effect. In some cases they cause light that would have otherwise penetrated to be reflected, and in other cases they cause light that would have been reflected to penetrate. But unless you can create a concave surface on your water (huge fan blowing directly down
), the ripple effect will not result in a net increase of light penetrating the tank. It will cause local, short-term, intensity variations, but no net increase.
Lets consider the light hitting the water surface in two parts - the light coming directly from the bulb, and the light hitting the water surface after bouncing off the reflector.
For the reflector light - since the light hits the water surface at close to 90 degrees, there is almost no spreading, so no real effect of height above water on light intensity enterring the tank. And we both agree that the reflector contributes more than half the total light penetrating the water surface, right?
For the light hitting the water surface directly from the bulb, the "lost photons" are those that hit the water surface at a flat-enough angle so that much of them are reflected by the surface rather than refracted into the water. This angle is unaffected by the height of the bulb. So, unless you raise the bulb really high (high enough that even the photons from the bulb that are coming down at high angle to the water surface would still miss the tank), you will have the same percentage of reflected versus refracted photons. And, if you have a hood around the top of your tank (instead of free-hanging pendants), some of the light that "missed" the tank because you had the bulbs mounted high will still bounce off the sides of the hood and hit the water. The only lost photons (lost energy) are the ones that hit the water at too shallow an angle to penetrate.
You mention ripple effect, and yes, ripples do have some effect. In some cases they cause light that would have otherwise penetrated to be reflected, and in other cases they cause light that would have been reflected to penetrate. But unless you can create a concave surface on your water (huge fan blowing directly down
), the ripple effect will not result in a net increase of light penetrating the tank. It will cause local, short-term, intensity variations, but no net increase.
