Effective use of your lamp

I am using my light for the third winter running. I adore my lamp & highly recommend it. Light therapy has adjusted my life! But today I didn't get round to using it until evening, and I feel quite alarmed at how the depressive symptoms are creeping up on me and suspect I have been using it ineffectively. When I use it in the middle of the day in a room with plenty of light surely the effect is dissipated? Whereas at night the glow is much stronger and concentrated. Evening use can interfere with sleep so I guess the solution is for me to take the lamp to a darker room and carry on using it during the day. As I say, I believe in these lamps 100% and would like others to get the best out of them.