I meant to do this weeks ago I'm so sorry--

idk how to explain much so if anyone needs clarification let me know and I'll try to help :'>

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start out with a flat colored base! I threw one together quickly so it looks kinda weird

next, hide the layer and create a new one under the lineart. set the layer effect to multiply and fill the entire thing with a purple/gray color! feel free to color pick the one I used

start erasing spots you want the light to hit, it doesn't have to be perfect, you can fix it

set the layer to clipping, if your art program doesn't have it then just erase everything around the lineart

this is what your drawing should look similar to,

after that, set a new layer to multiply and use a gradient to fill in your drawing with another purple/gray color

add another layer and set it to overlay, using the gradient tool fill in the area where the light hits

next, add a later above the lineart and use the magic wand tool around the lineart. select 'inverse selection' or whatever it's called

now that you can fill in the layer without anything going outside of the lineart, set it to overlay. use the gradient tool and a yellowish color to where the light hits (it'll look better with colored lineart, not black)

after that's done, use another overlay layer and add spots where the light hits it directly. I would recommend shading the fuck out of it, it'll look a bit better, you can also add a lot more effects if you want

add yet another layer and set it to add

use the gradient tool and fill it in with another white/yellow color

(I lowered the opacity)

after everything is done, you can do whatever you want with it- add more effects, a bg, whatever. this is what mine looks like,

feel free to tag me if you use this, I'd love to see what you make :'D