Shown here is a Luminated Decal of a QR Code using a low cost off the shelf LED-base used for 3D illusion lamps. And, like all of these lamps, the acrylic simply slides in & out of the base for easy replacement; however, unlike existing 3D illusion lamps, this one is in full color. The LED-bases receive power from a micro USB connector, or three AA batteries (for backup power or portability).
The example shown on the left would obviously be suitable for a shoe store/department. The marketing angle is to get the customer to come into the store and scan the QR code to find the discount. Once in the store, they may be more apt to buy something - not necessaily shoes, but who cares?
The QR code automatically routes a smartphone to a store's webpage that would provide details for the sale, so the store is in total control. With this approach, the store owner could develop their own algroithms to determine what discount is given when someone is directed to the webpage. Perhaps a bit of randomness to the discount makes it feel like a scratch-off lottery!
In restaurants, a QR code could be specific for each table, and a Luminated QR code would work great in this type of dark environment. Once a patron scans the QR code, the restaurant owner can have it land at the restaurant's order & payment system (hosted on-site or by a 3rd party). Look at the menu, order more drinks, split/pay the bill. Maybe even offer a free drink at the bar to open up the table for new patrons.
Luminated QR codes would also work well in storefront windows to engage passers-by, especially at night (although they're equally visible in daylight).