If the light inside the fridge stays on after you close the door, it could lead to inefficient cooling as the heat from the light interferes with your machine. While you may not always be aware this is happening, you can see whether or not the light goes off a fraction of a second before you lose interior visuals in most machines.
Additionally, if you suspect that the light isn’t turning off, you can touch the light bulb to make sure. If you want to make sure, however, you should figure out the light-switch button on the door of the fridge and press it to see if the light shuts off when the door closes. If it doesn’t, the switch is defective and needs to be replaced.