A lot of people like myself consider heat a form of light but I guess a photographer would be just thinking visible light. They say that about 50% of the sun's light emissions comes in the infrared frequencies.

That seems like a mistake since heat can transfer e.g. via contact without any electromagnetic emission. In fact, that is what I think happens with the sensor also, given that there is an IR filter in front of it.

But I may misunderstand your comment.

Visible light from the sun, or incandescent lights, is also emitted due to heat. Planck’s law is the mathematical relation if you want to know more.