I'd like to take three different Powers from 3 different light sources, values that normally are independent from each other, and link them by an equation. The equation I'd like them to follow is W1 + W2 + W3 = 400, to constrain the total power they output in this linear fashion.
By choosing W3 as a seed, I can then re-write W2 in terms of W1 as well.
Is there a way to link and automate the adjustments of these light sources in a easy beginner-friendly way?
Drivers come to mind there, but you have a math problem with your formula. What happens with W1 and W2, when you change W3, for instance?
You say you can use W3 as a seed and then write W2 as x times W1, if I understand that right...If you do that, you have a solvable equation and you can use a Driver that writes W1 (and thus W2) in terms of W3.
Is that easy and beginner-friendly? Probably not,
To give an example of how this could be done with Drivers (wouldn't call it beginner-friendly):
The Total (400 Watt) is 'hard coded' here, but it wouldn't be difficult to add another Custom Property for that.
If you want to play around, here's a link to the .blend:
https://drive.google.com/file/d/1NUkACNcy7hqo3zrcWHiuMveTPHpriEX3/view?usp=sharing