How do I reference a material in a driver?

TLDR: How do I take a value from a material (like base color) and use it in a driver scripted expression?

I am currently working on a test to try and extract the brightness and/or color data from a video texture and apply it to a light. I have a driver set up in the power property of the light, which uses a var referenced from a material containing the video texture. The driver panel then asks me for a “path” expression to complete the variable. I don’t know python. How do I take a value from a material and use it in a driver scripted expression? I am using an mp4 texture and Principled BSDF in the material.

You can right click the color or RGB values and select copy as data path or copy as new driver.