Infrared from the sun is a large part of light, it also has a massive wavelength compared to Ultraviolet, so even if you are inside a house with air conditionin

Infrared from the sun is a large part of light, it also has a massive wavelength compared to Ultraviolet, so even if you are inside a house with air conditioning and your central heating thermostat is showing 18DegC for an independent reference, you can still feel the sun. I say feel because its not a true "heat experience" but you know its hot and there is brilliant sunlight out there, even with blackout blinds for total darkness. I say a true heat experience because that typically involves UV radiation and visible light as well. I dont know if building wall thickness will effect it but InfraRed can penetrate the skin to quite a depth. https://www.icnirp.org/en/frequencies/infrared/index.html https://www.icnirp.org/en/frequencies/infrared/index.html IR penetrates the human skin and the eye to various depths ranging from several millimeters by IR-A to superficial absorption of IR-C