A far-infrared sauna is a type of sauna that uses light to create heat. "Far" describes where the infrared waves fall on the light spectrum. A traditional sauna uses heat to warm the air, which in turns warms your body. An infrared sauna heats your body directly without warming the air around you.
The appeal of saunas in general is that they cause reactions, such as vigorous sweating and increased heart rate, similar to those elicited by moderate exercise. An infrared sauna produces these results at lower temperatures than does a regular sauna, which makes it accessible to people who can't tolerate the heat of a conventional sauna. But does that translate into tangible health benefits? Perhaps.
Several studies have looked at using infrared saunas in the treatment of chronic health problems, such as high blood pressure, congestive heart failure and rheumatoid arthritis, and found some evidence of benefit. However, larger and more-rigorous studies are needed to confirm these results.
On the other hand, no adverse effects have been reported with infrared saunas. So if you're considering trying a sauna for relaxation, an infrared sauna might be an option.