You could either put a light (point light, that is) underneath the brush with the same colour values as the light_spot but with less brightness, or turn the texture of the light brush into a
texture light, which would remove the need for the light_spot as well.
You can modify/use lights.rad as the tutorial states, or add an info_texlights (might not be in your FGD, but should still work with modern compile tools) with the name of the light texture and the colour/brightness value as entries.