Siesta period is mentioned in Peter Hiscock's book "Enciclodedia of Aquarium Plants". Quote:" Plants are able to regulate the rate of photosynthesis relatively easy and quickly respond to changes in light conditions. In other words, they do not take long to warm up and start photosynthesizing once there's sufficient light. However. algae are not as biologically advanced as plants and need a long and relatively uninterrupted period of light to function properly.....If the aquarium reeives 5-6 hours of lighting followed by 2-3 hours of darkness and then another 5-6 hours of light, plants will be relatively unaffected and receive enough light throughout the day, but algae growth rates will be significantly reduced and may even start to die back."
I do follow this routine on both of my planted tanks. It does work as it claims: plants don't mind it, algae does.