I planted a Sequoiadendron giganteum (Giant Redwood) sapling today, and I was wondering how many hours of daylight the little guy needs. I found this answer, which mentioned photoperiods of different plants. I haven't been able to find any kind of index of these values by species, and I was wondering if such an index exists. If not, is there some other way I can find out the natural photoperiod of a given species?
Most plants don't care directly about day length for growth. Some have timing requirements to bloom. E.g. Strawberries come in 'june bearing' and 'day neutral' varieties. I don't know if the June ones are triggered by a minimum day length, or a maximum night length. Poinsettias require N days of more than 14 hour long nights to bloom. Spruce use day length to start the process for fall adaptation.
The difference in illumination between full sun and indoors is truly astounding. Your eyes are very good at adjusting to lower levels of illumination. Yes redwoods will grow in the shade of their parents, but they grow VERY slowly. Still, your window has more light than the forest floor of a redwood grove. It should do alright there. Turn it a third of a turn once or twice a week.
I don't know if the day length requirements for redwoods has been determined. In passing however, they do fine in Vancouver B.C. (Don't know if they are coastal or big tree) And Britain's forestry service is considering redwoods as a tree for planting as climate change hits the isles.