Nice, but:
"Since the device is a light bulb, it would be difficult to detect and likely to go unnoticed."
I doubt it would be any harder to shut down than any other public-access WiFi device, just a bit of experimentation with turning off power / devices would find it.
Just walk around with a Wi-Fi analyzer on your phone, playing hotter/colder until you find it.
Modern enterprise access points even have built-in functionality to physically locate devices, and automatic warnings for rogue access points. The latter is often ignored or disabled though, because it'll go off every time someone prints or screen casts over Wi-Fi Direct.
So many objects have their own networks now. With a clever SSID and placement in a room full of potential targets, it could be pretty tough for someone to narrow it down to the bulb.
I think the point was that it's difficult to notice in the first place, not that it would be hard to find once you know you're looking for something. You don't have a black WiFi router with antennae dangling down from the ceiling.
If you went the other direction and didn't worry about it being noticeable, it would be kind of a fun project to break up a book into a series of QR codes. A scavenger hunt, with each code's text ending with a clue of where to find the next?
while true i think it's extremely unlikely to be suspicious of a light bulb. especially if it doesn't seem out of place, like if it's on a light socket why think that it's an wifi access point?
New device design: battery backup for the computer, light still operates based on external power.
This would be a massive improvement. I wonder what the largest battery you could fit in would be.