Final answer:
Infrared rays are the type of light that penetrates tissues and provides a soothing effect, being commonly used in heat lamps for muscle relaxation and improved circulation.
Step-by-step explanation:
The light rays that penetrate into tissues and are considered soothing are infrared rays. Unlike X-rays, which have higher energy and can penetrate soft tissues, infrared waves have lower frequencies and longer wavelengths. They are absorbed more by water and carbon dioxide molecules, making them less penetrative for deep tissue but ideal for superficial soothing effects.
These properties of infrared radiation make it commonly used in heat lamps, which provide a warming sensation that can relieve muscle tension and improve circulation in the skin and nearby tissues.