By Laura Brown By Laura S. BrownBusiness Insider/Tanya F. PomeranzThe light you see at night is the energy of your room.

It’s the light you use to run the thermostat, open the windows and get the air conditioning going.

And it’s the energy that’s used to illuminate your TV.

It’s important to recognize that light at nighttime doesn’t always come from the sun, but from some other source.

Light from the earth can also give off energy.

And some people in our world, especially those in urban areas, are using outdoor light sources to illuminate the room at night.

This article originally appeared on Business Insider.