it's the timing.

That is true but not everyione's circadian clock runs on the AM light.
Some people's SAD is better heped by lighting another time of day for the really-bright light. For some it's bedtime.

Around noon, usually, for me. Think of summertime-- what time of day does one most enjoy being out and about. (Instinctive body systems at work.) It varies for most of us... But whatever that time is, that is probably the time supplemental bright light is needed. For me, too-bright at other times is a real problem. I discovered this summer that my best ambient lighting to spend any amount of time in is partial shade, with short afternoon bursts of hard light. (I use my impatiens plants to discover where to leave my chair.)

~S~