With the exception of a few species, fish do not require special light for health. In fish-only tanks, lighting should minimise the growth of algae while maximising the colour of the fish. In tanks containing coral and plants, the spectral distribution of the light becomes a factor. For the coral and plants to survive, there must be adequate amounts of light in the blue and red regions for the spectrum to allow for photosynthesis. The light should also be of sufficient intensity for plant respiration. The amount of light should be tempered, however, as too much light could startle the fish. Typical set ups have alternating 12-hour periods of light and dark. To prevent fish startling, a blue/actinic lamp is used before the white light source is turned on.