how many hours of illumination is too many?

[louis_last]

When it comes to how many hours you should light your tank for I have seen many contradictory figures, all of which presumably take into account the needs of both the plants and fish, shrimp, etc.
In a tank with only flora and no fauna is there any reason why you shouldn't leave the lights on 24 hours a day to promote growth? this can certainly be done for many terrestrial species, is there any negative effects from doing so in an aquarium?

[Robert]

Hi,
most higher plants have a fixed photo period. They can't use it without rest 24/7. So it won't make much sense to turn it on all day long. About 14hours is the maximum for most plants (at least that's what I learned during my biology studies in the advanced botany course). For a normal tank 8-12hours will do. Heteranthera zosterifolia shows it clearly when it got long enough light. The leaves will stand up.

regards
Robert