Select the hotbar slot containing the torch icon and place one the ground a couple blocks away from your machines. This will supply light, as well as heat when you stand near to them. The suit indicator in the top right of the screen indicates the external temperature and the internal suit temperature. Your suit will automatically keep yourself warm, but this costs energy. If you stand near a torch, you will see the external temperature rising, which means your suit uses less power to keep you warm. Watch out with getting too hot though, that will make your suit spend power to cool you back down!