Yesterday I was standing by the campfire. I used to think that campfire heat carried to me only by air. It was heating my face too much, so I blocked it with my hand just like blocking the sun. Then area on face which is shadowed by my hand stopped getting heat from campfire. Then I thought if it were getting transferred only by air it would pass by around my hand, and something that travels in straight line must be transferring most of the heat. But yet the campfire does not look so bright. Is it some kind of radiation, invisible light?
Yes, infrared radiation which is invisible to human eyes but still radiates heat. This is how they make thermal cameras, they are using your body's infrared radiation which is detected by the camera and forms an image based on visible light.