“The near-infrared radiation (NIR) window, also known as the “optical window” or “therapeutic window”, is the range of wavelengths that has the maximum depth of penetration in tissue.” This definition of NIR explains to us that this wavelength is used in diagnostic medicine because they are able to penetrate the deepest below human tissues to allow us to take a glimpse within the human body. This non-invasive diagnostic tool allows doctors and scientists to see things that they might not be able to see otherwise, such as tissues of the brain.
In comparison to red light waves, which are utilized for more superficial medical treatments, NIR wavelengths penetrate deep within the body’s tissues. To put these differences to scale: Red light emits 600-690 nanometers, whereas NIR is significantly higher at 800-2,500 nanometers. This is why NIR is useful for treatments of tissues that lie deeper within the body, such as organs, muscles, lymph tissue, and even brain tissue, just to give a few examples of the power of NIR.
One of the most common uses of NIR in a medical setting is a pulse oximeter, a device that anyone who has gone for a check-up at their doctor’s office or has been in the hospital, would recognize. This is the little device that can be placed on your fingertip to get a reading on your pulse in addition to oxygen saturation levels in your blood. One of the most recognizable features of this device is the little red light on the end. This red light (NIR) allows medical professionals to gather important data such as how much blood flow/oxygen is saturating the tissues of your body.