Blue light suppresses the release of endogenous melatonin. To get an idea of how much it suppresses, it, take a look at the image below. In this image participants were exposed to no light, or a 2 lux light at 460nm (blue line) or 560nm (green line) for 1.5h. source
As for the mental stimulation part, that’s going to vary a lot more from person to person and how engaging the content is, but you’re right that being mentally stimulated in the wrong ways can keep you awake too.
Blue light suppresses the release of endogenous melatonin. To get an idea of how much it suppresses, it, take a look at the image below. In this image participants were exposed to no light, or a 2 lux light at 460nm (blue line) or 560nm (green line) for 1.5h. source
As for the mental stimulation part, that’s going to vary a lot more from person to person and how engaging the content is, but you’re right that being mentally stimulated in the wrong ways can keep you awake too.