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Techie solution for Sunlit tank

Nerd alert: techie posting
>...contemplating renovating his roof to take advantage of natural sunlight for his aquariums.
>I know from personal experience that algae and temperature could be a
>problem but I thought I would post the question to you experts out there (or
>anybody who has experimented with this).  What are the inherent advantages
>and disadvantages of using natural sunlight for aquariums?  My friend lives
>in Indonesia so the sunlight intensities shouldn't vary too much throughout
>the year.
	Here's how I would handle it (granted, it's a techie solution, but
maybe it's a starting point.)
	1. Put a photocell at the surface of the water.
	2. Simple electronic circuitry continually monitors the amount of light
falling on the tank surface over time.  If a certain light level is
exceeded, louvers are closed (or in a more sophisticated setup,
partially closed to produce the right light level.)
	3.  A more practical and simpler setup would be to set up the tank so
it's getting the desired amount of light on a typical sunny day -- so
that even at high noon on a cloudless summer solstice (i.e. worst case,
or is it best case?) the light is not excessive.  If the photocell
light-monitoring circuit then determines that the light is
*insufficient* for too long a time, it would turn on the tank lights.
	This could turn into a Wretched Excess engineering exercise, with a
supervisory personal computer, or (my preference) done with a handful of
Radio Shack-level parts: the photocell, a 555 timer chip, a relay -- the
$10 DC power supply would be by far the most expensive component.  Just
add $1000 worth of your time :)
	Advantages: Perfect solar spectrum, energy cost savings, aesthetics.
	Disadvantages: Time to design and build circuitry.
In the tropics, where electricity is often expensive but sunlight is
plentiful, this might be a worthwhile exercise.
Sherman Lovell -- in Seattle, where even in mid-July we don't worry
about excessive sunlight, and the tank heaters' neon lamps are still
glowing.