As well as looking pretty fancy and impressive for when guests come round, photosynthetic life (i.e. corals, plant life etc.) is basically integral to the ongoing equilibrium of your aquarium, so it’s imperative you take good care of it. Obviously, (as we’ll get to in a bit) a certain level of near UV light is necessary to keep these organisms ticking along nicely, but, as is the question on every professional and hobby aquarium keeper’s lips, is how much is light is just right? It’s a common (and often damaging) misconception that you should have your aquarium lights on 24/7, doing so, however, can prove not only wasteful but harmful in the long run.

The Lights Are On…
Apologies for briefly returning you to the haunting memories of GSCE science, but it’s important to remember that photosynthetic matter effectively converts near UV light into a usable energy source, and is thus integral to keeping a healthy tank. Decent aquarium lighting is normally of a high enough voltage to provide a sufficient amount of light for your plants to grow and develop, but as yet there are no unified guidelines as to how long you should leave your lights on for.
Research suggests that marine plant life has a phyto cycle of approximately 7-8 hours which, in normal English, just means that after this amount of time, they can’t physically absorb any more light. Thus, leaving your aquarium lights on for any longer than this means that all of the near UV energy they release is simply being wasted.
…But Nobody’s Home
Here at iQuatics, we’ve been collectively keeping tanks for over half a decade, and we know that keeping your aquarium lighting systems on for extended periods of time can actually prove to be very expensive when that energy bill lands on the doormat. What’s more, leaving your fish tank lighting on for more than the recommended 7-8 hours per day can actually damage your plant life, and destabilise your ecosystem.
Though there’s little confirmed research, a variety of users across multiple aquarium keeping forums suggest that too much light has resulted in physical damage to their plants and corals, claiming that they noticed discoloration and signs of burning that are akin to light damage in traditional plant life. It could be the case, however, that in these instances their aquarium lighting was either too intense, or too close to the tank.
Striking a Balance
As with a lot of aquarium keeping conundrums, the question of ‘how much light is right’ will ultimately come down to trial and error. It is recommended that you shouldn’t regularly exceed 7-8 hour periods of intense lighting, regardless of the size of your tank. Possible warning signs of a lack of  near UV light include an anaemic discoloration and wilting affect across both plant and coral life – so they’re really things to be looking out for. iQuatics professional tank keepers, however, reiterate that under no circumstances should your aquarium be constantly lit; it’s important to maintaining a healthy equilibrium to afford your marine vegetation some rest time on a regular basis.