I'm going to start this off by admitting something up front. I didn't build this the right way. Well, let's mellow that a little and say I didn't build this in the most optimal way. Sometimes you already have some infrastructure in place beyond simple networking and when you tinker with new sensors you just use the infrastructure you already have. Then later, when you want to extend your project from tinkering to the cloud, you have to jump through some hoops to make it work. If you want to skip what I actually did and just read about how I should have done it, just click on "The Right Way to Have Built This!" on the left side navigation bar.
So, on with the project! I bought one of the then-new Adafruit GA1A12S202 log-scale light sensors to tinker with (it's been around for a while now). At the time, I was teaching myself Lua so I could program the ESP8266 using NodeMCU. What a perfect project, I thought! I'll use the Feather Huzzah 8266 and the light sensor to record the light levels. At this point, I wasn't thinking about Adafruit.IO, I was just thinking of grabbing some light level data.
Skip forward to this morning when I woke up at 1:05 AM and couldn't get back to sleep. "I should hook that sensor platform up to Adafruit.IO," thought I. And I got to work. This tutorial talks about how I did what I did. Oh, and yes, it does work.