My guess is that a boiler was recently removed while there was still hot water in the steam engine. You can even see the steam. The radar drains most of the remaining energy output.
I'm not sure how lamps are supposed to behave in low-power conditions.
I tried to replicate but I don't have any savegame at night...
The symbol of the energy means, that the energy dropped under certain value percentage (10% to be exact).
This can still be enough for the lamp to partially work.