There's a headlight bulb, a turn signal/parking light bulb, and a 3rd little bulb in the small circular part of the housing. What's the function of that bulb?

Sounds like a stupid question, but I just painted my headlights and was putting them back on and after I finished the passenger side one, that bulb isn't lighting up. It's connected, so unless it's burnt out, I dunno what's wrong.

I just want to know if that bulb is significant or not. Thanks for any help with this.

 

the third bulb is like a city light on jdm head lights it is not bad if you don't have it not a main thing like a headlight or turn signal or anything you should be good if you put a turn signal on an it flashes fast then that bulb is related to that third bulb most likely the bulb is bad try to change it and see but i am almost 100% sure that it is not anything but a city light