I thought that, too, but it turns out that the rubber gasket on most refrigerator doors allows for enough signal leakage that network devices will work from inside the refrigerator. A number of community members have sensors in their refrigerators as I found out in the following topic:
As to whether or not the device has to be smart, it really depends on whether you want something that will for example let you know if the door was left open. If not, no need for a network.
If it was me, I would just buy a couple of inexpensive motion detector lights that are rated for outdoor use and try them in the refrigerator until I found one that worked to my satisfaction.
My personal favorite nonnetworked brand is Mr. beams, which are very good quality, but do cost more than some others.
http://www.amazon.com/Beams-Battery-Powered-Motion-Sensing-Stick-Anywhere-Nightlight/dp/B002FCGI8Y
Regardless of brand, if you have a problem with the light not coming on because the room is too bright, try just turning it around and aiming it towards the back of the refrigerator, or aiming it across the refrigerator but putting it inside a box. You may have to intentionally wave a hand in front of it but the light should come on and stay on. So it’s just a matter of getting everything angled just right. Or, as others suggested, just use opaque tape over the light sensor.