Don,
I use natural light on my two reefs, but not direct summer sunlight because of the dramatic rise in tank temps. Both reefs are on the east wall, so in summer I keep the blinds closed until the sun passes and does not shine directly on the tanks. This time of year, the sun is weak and doesn't heat up the tanks, so I keep the blinds open all the time.
Here's my 72 gal bowfront with the blinds open:
Here's the tank area of my living and dining rooms. Right to left, 72 gal bowfront, 42 gal hex, 28 gal SH tank, ball python terrarium (with the red heat lamp):
The 42 hex has light coming at it from three sides
