If you have a new fridge that is really energy efficient and has really big door seals that are prone to sticking and not closing all the way I suggest that you replace the incandescent bulbs with LED bulbs.
Our AMANA fridge came with 2 40 watt incandescent bulbs in the fridge and one in the freezer. When we left the door on the refrigerator ajar overnight last year the bulbs pretty much cooked all the food. It melted all the butter. We threw away everything. I replaced those bulbs with these little 1 watt LED spotlighters (20watt equivalent) at 9.99 apiece at the local hardware store. Now we don't have heaters in our fridge.
Like an idiot I forgot to change the one in the freezer. Last week we left it ajar and it melted everything. Including some really nice buffalo steaks and some frozen fish that cost way more than the 30 dollars in LED replacement. I think there are real LED fridge bulb replacements out there, but the little spotlighters were easily available in my local hardware store and fit in the space of the incandescent appliance bulb.
I am not saying that leaving the fridge open is now a painless exercise, but I am saying at least you won't be actively heating your food while your fridge is open. The new fridges are so well insulated that a couple of 40 watt bulbs can actually cause the fridge to melt/burn ( according to our appliance repair man).
So in conclusion. You will save a fairly minimal amount of energy as the bulb is off when the fridge is closed, but you will save yourself a whole bunch if you accidentally leave the door cracked. The bulbs do heat up really fast. By the time I opened the refrigerator, removed the cover and started to remove the bulb they were already too hot to touch.
Or you could be not-an-idiot and never leave the door open. I recommend this path the most, but I find that the seals on our fridge are sticky enough that they defy me regularly.