I had gotten a light a few months ago, it sits atm.

The morning time frame, I would get really agitated and irritable, so I tried it in the afternoon (read some people who have mixed or rapid cycling episodes may benefit with the afternoon session ) so I took it in to work,..... and didn't feel it had a positive out come, I was less agitated and irritated but didn't feel it was assisting... I did use it a few times around 4pm-5pm where I had thought perhaps it may have helped, but I was staying up later which didn't work for me.
I had some what forgotten about the light, if I am honest . But now I'm wondering if I should give it another shot since I my mood has dropped even more than a few months ago.

I started with 10minutes, but most light sessions were 30 minutes.

I had gotten it in hopes of a "more natural " remedy... Years ago in the winter I did my first (and so far last) tanning beds and felt so up lifted for a day, I had hoped the "happy lamp" would assist.

Light therapy - Mayo Clinic
Seasonal affective disorder treatment: Choosing a light box - Mayo Clinic