In 1967, Hungarian scientists were investigating the use of a red light laser to treat experimental tumors in mice, hoping to cure their cancers with red light. Although it did not cure or improve the tumor, they noticed that the wounds healed faster, and the shaved hair regrew remarkably fast. This was the first documented use of red light therapy. It has since been utilized for multiple medical conditions. 
Red light and near infrared light, with wavelengths of approximately 650 nm and 850 nm penetrate tissue, and give a gentle stimulus to the hair follicle. 
In every cell of our body, an organelle known as the mitochondria produces energy. Electrons flow through 4 complexes known as the electron transport chain, and as they flow energy is produced. Sometimes complex 4 becomes blocked by inhibitory nitric oxide. Red light disassociates nitric oxide from complex 4, which restores electron flow and energy production. 
More energy in the cell means that it can perform its normal function better. In the cells of the hair follicle, this means that it can grow better.
The main action of red light and near infrared light is better energy production in the cell. Other actions include: decreased inflammation, prolongation of the growth phase of the hair cells, and greater blood flow in the skin, which translates to better hair growth.
The stimulation of hair regrowth has now been documented in multiple high quality studies. The average effect size is 1.0-1.4, which is considered a large effect in medicine.
In the average study, hair density increased by 15-25 terminal hairs after 16-26 weeks of therapy. This is a significant increase.
In our clinic, we utilize red light therapy as one of three prongs of our hair restoration program. The other two components are micro-injections of exosomes (a stem cell product), and daily use of a topical serum and shampoo. 
Please contact us if you are interested in a discussion and possible treatment of hair loss.