Kelly, it is very dangerous to compare light levels in nature with those behind a glas window!
Almost all high energy UV-light has been filtered by the glass and this can have a huge impact on light demands for flowering.

There are also alot of other factor in flowering that you forget. Your total growing conditions differ enormous from the commersial growers greenhouse and even more from the plants natural habitat.

I though agree with Maura that a inexpensive light meeter that give you a roughly value is a very good investment, as the human eye is extremly good to adopt to different light levels and we are unable to correlate light levels.

Edit: and I agree with Amey Bhide above that manage to post just before me .