Thanks for asking! I haven't documented it anywhere, and the source code isn't suitable for consumption by others. But, I can tell you about the basics.
I bought a "12V" LED strip intended for automotive use, and created a simple circuit with a +12V DC supply and an NPN transistor. By hooking the NPN transistor to a PWM output on the Pi's I/O (via a resistor), I can control the LEDs from nearly full darkness to their maximum brightness. Here's a tutorial that covers the same ground: https://dordnung.de/raspberrypi-ledstrip/
There's also a switch for "disable alarm no matter what" and "turn light on/off right now". (I also use it as a nighttime reading lamp, with the added bonus that it starts ramping down the brightness after about 25 minutes and turns off after 30: a good reminder to go the f--- to bed)
This all hooks to some not very interesting software to listen to the buttons, carry out an alarm schedule, ramp the LED intensity up and down, and so forth. In my case, it's written all in Python in a sort of timer-and-event-driven style.
Since this pi has wifi, one part of a traditional alarm clock is missing: it sets the time from NTP and applies the standard DST rules to obey summer time; there are no controls to set the time, and even after a midnight power outage it'll generally alarm at the right time in the morning, as long as power came on at least a few minutes before the appointed minute.
I've had a number of variations on homebrew light alarm over the years, AVRs and arduinos, TRIACs switching standard incandescent lamps, RGB LEDs simulating the sunrise color sequence, etc. It's the sort of project you can always do again and explore more of the problem space and find what works best for you.