Exposure Lock (AE-L Button) is the abbreviation stands for Automatic Exposure Lock. It is useful using automatic and semi-automatic shooting modes.
This charts show the effect of aperture on the size of the starbursts. As you can see, the smaller the aperture, the more emphasized the starburst. The same concepts apply during the daytime as they do during the night time.
How to Take Night Pictures Of Scenery from SnapHappyMom.com