Baby Monitor 3G has an option to turn on the light of the phone when the baby's room is too dark or when you want to get baby's attention. It can be turned on while the video is active by tapping on the flashlight icon.
If you are missing the button could you please check, if your Baby Station has functioning flash?
If the Baby Station doesn't have a flash, but the front camera is present, you can switch cameras within the app, and use the display as a source of the light instead of a flash.