Can a seedling grow in a 12 hour light period?

[StoneMeadow]

I'd venture that in your sunroom, yes. Especially an indica strain.

Ah, that's good to know...thanks!

How old/new are your windows in that room?

Are they double pane windows?

Are they energy star rated?

If you have relatively new windows with a high energy star rating the light is filtered a lot. The Low-E glass and argon gas in newer windows wont let very much good light in. The plants may be in full sunlight but still wont get all they need cause about 30% or more of the light is filtered out. It looks like there is plenty of light but it's not good light.

Just food for thought

Good points...thanks! The room was built by a previous owner of single-pane 3' and 4' wide sliding glass doors. The Guardian brand is etched in the glass, along with ANSI Z97.1-1975,the words "Safety Tempered" and some other what looks like production coding, but nothing about about energy star or low-e.

In any case, my tomatoes, sweet peppers, zucchinis and other veggies do fine behind them. I was really just curious if natural daily winter light alone was simply too short for the plants to bud out. I live about an hour's drive outside San Francisco at 38 degrees north.