First time commenting here. A friend linked this thread on Facebook, and have something to add about the possible mechanisms of light therapy.
So far as I am aware, the mood and concentration enhancing effects of light therapy work primarily on the Serotonin -> Melatonin synthesis that occurs in our brains.
Basically, when it gets dark and gloomy, our brains start manufacturing melatonin, to make us feel tired and sleepy. In animals such as bears, the winter induced melatonin is a signal that it is time to hibernate.
The interesting part is that the chemical from which melatonin is synthesized is serotonin, which as we know is involved in mood, appetite, sleep and all sorts of human behaviour, and is the primary neurotransmitter system targeted by SSRI antidepressants.
Hence less light causes more serotonin to turn into melatonin, which makes us feel both tired and potentially moody. Therefore its reasonable to hypothesize that light therapy works by reducing the rate of melatonin synthesis and maintaining higher levels of serotonin.
I have never heard of light therapy affecting adenosine levels in the brain. This doesn't mean that it doesn't, just that I am unaware of evidence that this is the case. A quick pubmed search didn't reveal any papers to back up this hypothesis either.
In my personal mood and productivity experimentation, I have found that supplementing my diet with 5-hydroxy-tryptophan (5HTP) in addition to using a high lux lamp does wonders for my mood and productivity (sorry I cannot quantify "wonders").
Basically, the synthesis path normally goes: Proteins -> Amino Acids (including tryptophan) -> 5-hydroxy-tryptophan (which is capable of crossing the blood brain barrier, and does so but in competition with other amino acids) -> Serotonin (5HT) -> Melatonin (when dark or in low light, technically a lack of light hitting the retina).
So, potentially supplementing with 5HTP or another source of tryptophan in addition to light therapy should be more effective at enhancing mood/productivity by both increasing the rate of serotonin synthesis and decreasing the rate of serotonin metabolism. Assuming serotonin is responsible for these effects, of course.