Night View Coral Fluorescent – Atlantik V2 Moonlight
There are many aquarists who feel that moonlight is an important part of the photoperiod required for corals; this is not the case at all.
Moonlight is purely for visual effects and it serves no purpose for coral growth. In fact it can do harm to corals if used throughout the evening.
Corals, like terrestrial plants need a photoperiod break or rest to carry out the biological processes that are required for good healthy growth. Keeping your moonlights on throughout the night can have a negative reaction to your corals by not allowing them the rest they need. Real moonlight produces no more than 0.2 and a high of 1 Lux in tropical latitudes. There is no measurable PAR but corals do sense the light being emitted because the moon reflects about 13% of the sun’s rays.
Moonlight appears blue but there is no blue in it and this is known as the Purkinje effect ***.
The first thing that will come to readers minds is the Lunar Cycle and why this does not affect the growth of corals in the wild. The answer is that the Lunar Cycle consists of 14.7 days of moonlight and 14.7 days of darkness. During the moonlight phase, Lux levels vary from 0 to not more than 1Lux.
Jan Evangelista Purkinje (1787-1869) was a professor of physiology at the University of Prague. He is credited with a number of scientific discoveries, including the discovery of Purkinje cells, which are large nerve cells found in the cerebral cortex. However as a young man, he made a simple observation – something we have all probably seen – but because he noticed what he saw, and thought about it deeply, he came to some interesting and original conclusions.
He was keen on walking outdoors in the early morning, before it was properly light. He noticed that his favourite red flowers, which seemed so bright in normal daylight, seemed so much darker relative to the surrounding leaves, when viewed in very low light conditions. This has become known as the Purkinje Effect, and he speculated that humans have two separate systems for seeing, one that is used in bright light and one that is used in low light conditions.
We now know that the human retina has two types of cells, cone cells and rod cells. There are about 4.5 million cone cells in the retina, and they are responsible for colour vision. There are normally three types of cone cell, but overall they are most sensitive to yellow light. The rod cells, of which we have about 90 million in each retina, work at very low levels of light, but cannot distinguish between different colours, which is why everything seems to be black and white at low light levels. However the rod cells are most sensitive to the blue/green end of the spectrum.