Explain red light therapy wavelengths

**Wavelength-Dependent Penetration and Effects: A Comprehensive Review**

Photobiomodulation (PBM) is a process where low-level light therapy (LLLT) stimulates cellular responses, promoting tissue repair, healing, and relaxation. The wavelength of the light used in PBM can significantly impact its penetration depth and therapeutic effects.

**Wavelength Range and Penetration Depth**

Research has shown that different wavelengths of light penetrate to varying depths in biological tissues. Here is a summary of the penetration depths for various wavelengths:

* **610 nm**: not extensively studied, but may have similar penetration depth to 660 nm red light
* **630 nm**: typically penetrates to 2-4 mm, with some studies suggesting up to 6 mm
* **660 nm (Red)**: typically penetrates to 1-5 mm
* **680 nm**: similar penetration depth to 660 nm red light, with some studies suggesting up to 4 mm
* **700 nm (NIR)**: can penetrate deeper, reaching up to 10-20 mm
* **740 nm**: similar penetration depth to 700 nm NIR, with some studies suggesting up to 15 mm
* **760 nm**: typically penetrates to 10-20 mm
* **800 nm (NIR)**: can penetrate even deeper, reaching up to 30-40 mm
* **830 nm**: typically penetrates to 20-30 mm
* **850 nm (NIR)**: can penetrate extremely deep, reaching up to 50-60 mm or more in some studies

**Wavelength-Specific Effects**

The therapeutic effects of PBM also vary depending on the wavelength used. Here is a summary of the potential benefits for various wavelengths:

* **630 nm**: effective for skin and superficial tissue, may be beneficial for conditions like acne, rosacea, and psoriasis
* **660 nm (Red)**: effective for skin and superficial tissue, may be beneficial for conditions like acne, rosacea, and psoriasis; limited penetration depth may affect its efficacy for deeper tissues
* **680 nm**: similar effects to 660 nm red light, with some studies suggesting up to 4 mm penetration depth
* **700 nm (NIR)**: effective for deeper tissue penetration and effects, may be beneficial for conditions like muscle pain, inflammation, and wound healing
* **740 nm**: similar effects to 700 nm NIR, with some studies suggesting up to 15 mm penetration depth
* **760 nm**: typically effective for deeper tissue penetration and effects, may be beneficial for conditions like muscle pain, inflammation, and wound healing
* **800 nm (NIR)**: effective for very deep tissue penetration and effects, may be beneficial for conditions like joint pain, arthritis, fibromyalgia, and cancer treatment
* **830 nm**: typically effective for deeper tissue penetration and effects, may be beneficial for conditions like muscle pain, inflammation, and wound healing
* **850 nm (NIR)**: can penetrate extremely deep, reaching up to 50-60 mm or more in some studies; potentially beneficial for conditions like joint pain, arthritis, fibromyalgia, and cancer treatment

**References**

Bashkatov et al. (2005). Optical properties of human skin, subcutaneous and mucous tissues in the wavelength range from 400 to 2000 nm.

Ash et al. (2017). Effect of wavelength and beam width on penetration in light-tissue interaction using computational methods.

Hamblin et al. (2016). Shining light on the head: Photobiomodulation for brain disorders.

Please note that the penetration depth and effects of wavelengths can vary depending on individual factors, such as tissue type, intensity, and duration. These values are approximate and based on available research.