A green light is good. It means that your See.Sense. is registering movement, which is what it is designed to do.
In this scenario, the most likely cause is that the unit is not sufficiently vertical. If it is not vertical, See.Sense. will ignore rotation events, this prevents it coming on when not on your bike.
In order to activate your See.Sense. align the lens with something vertical (such as a door, wall or bookshelf) and then rotate alternatively left and right until the fuel gauge starts to flash (if turning on) or the unit deactivates (if turning off).
We've created a short video to help explain how to turn your See.Sense. on and off easily.
Failing that, your See.Sense 2.0 light could have newest firmware loaded onto it. In this case, whilst the light is on, simply point the light face down onto a solid surface like a table, desk etc. and the light should turn off after a few seconds.