1- It’s very easy to test: put mices in environment with and without infrared, measure inflammation markers, repeat with humans, correlate markers with diseases.
2- You can measure the level of infrared in environment vs outside. I don’t know what is the power difference. Without knowing all the details, the best way is to get in the sun.
3- How does it work: infrared penetrate deep in tissues, you can test with a red light through your hand or mouth, etc, infrared go deeper than red light.
The mitochondria use infrared to synthetized melatonin that remove free radicals. This happen even inside the brain, the infrared get there.
The melatonin produced at night is merely the backup plan for our body when the sun isn’t there.
There is a strong tendency to assume that what we don’t know doesn’t exist (pseudoscience) but we should do the opposite, assume that everything from the natural environment is connected to our body.
I am sure that vit-d was considered impossible before, so was most of what we understand today about our body.
Look at medcram and infrared, you will find that there is credible research around this.