FDA allows advertising red and infrared for minor pains and mild arthritis. Red has been used to help halt dry macular degeneration which may have FDA approval. The following have FDA approval for specific devices: infrared 880 nm for diabetic peripheral neuropathy, 660 nm red for mouth ulcers in children on a type of chemo, “Titan” intense infrared device for wrinkles in a clinical setting, very intense (harmful) infrared devices for spots, and blue or blue/red for acne. There have been excellent results reported for tendonitis, shoulders, knees, small joints, and fibromyalgia. For most soft-tissue injuries beneath the skin, the pain goes from an 8 to a 2 (on a scale of 10) after an hour or two of treatment with good home-use LED devices. For exposed injuries like burns and retina injuries, only 1 to 10 minutes of LED light is used, depending on the device. Applying LED light for too long cancels the benefits, so the time of application is hard to determine and important: too little light and there is little benefit, and too much light and there is no benefit. The pain relief can be amazing in burns, cuts, and other wounds even if wound healing is not faster. The increase in the speed of healing can be directly measured in the injured retinas of rabbit. It does not help bruises. Stubbed toes can go from being purple-black to pink in one treatment. Serious injuries seem to benefit from 3 to 6 treatments/day (as the pain returns) instead of one treatment/day. Strangely, tendons sore from working-out seem to not receive any pain relief, but chronic tendinitis seems to benefit greatly. It is beneficial only about 30% of the time in back pain. Companies have made various strange claims: yellow for wrinkles, green for cancer, and blue for wrinkles. Recent serious injuries benefit from several treatments per day.

Why does it work?

The wavelengths from 600 to 900 nm pass through blood and water in tissue more easily than other wavelengths. About 35% of the energy in this range is absorbed by a specific “proton pump” (cytochrome c oxidase, CCO, “complex IV”) in mitochondria. The light at 4 specific wavelengths “kick-start” the CCO pump into producing more cellular energy, ATP. The CCO pump is very similar in all animals because it evolved from light-assisted bacteria that were part of the first mitochondria. The absorption spectrum of blood suddenly drops off to allow these wavelengths to pass through which indicates the evolution of hemoglobin may have been influenced by cells benefiting from these wavelengths. The immediate increase in respiration that sun causes by this mechanism may help animals increase their activity during the day, in addition to the heat provided by the sun that promotes the release of oxygen (myoglobin also absorbs these wavelengths). These wavelengths of the Sun can provide the optimum 4 J/cm^2 at a depth of 1 inch (using 1% transmission) after 4 hours of exposure in bright Sun, reaching all skin and a large percentage of muscle tissue in historically-thin humans with minimal clothing.

Evolution Theory Support: There are 5 indications that the benefit of red and near-infrared light is not an accident, but a highly “intelligent” and natural result of evolution. The indications are: 1) The proton pump is the last in a series of 3 pumps which places it in possibly the best location to pull the food conversion process along by “pushing” the final electrons through the chain. This creates electrostatic pull on the electrons further back in the chain. 2) The pump absorbs primarily the red and near-infrared light and the remaining sunlight wavelengths are blocked by water and blood. 3) The pump is the primary absorber of these wavelengths in the body, very roughly about 35%. 4) Oxygenated hemoglobin has a very sharp decline in it’s ability to absorb red and near-infrared which indicates hemoglobin evolved specifically to allow these wavelengths to pass through. The CCO pump has a longer evolutionary history than hemoglobin because it was inherited from bacteria that formed the symbiotic relationship in mitochondria. Decendents of these bacteria still exist as purple bacteria which are used in most research on the CCO pump. 5) Night-time levels of melatonin, but not day-time levels, have been shown by Tiina Karu to completely inhibit the positive effects of infrared light. This indicates that melatonin and its wide swings over 24 hours could have evolved to not inhibit the benefits of sunlight.

Details on cytochrome c oxidase: As the CCO absorbs light, its two copper atoms are either oxidized or reduced to transport electrons that are required to help pump H+ to increase the gradient that allows for more ATP. This increases respiration (krebs cycle molecules provide the energy). Calcium Ca²⁺, alkalinity (0.2 units), and oxidation are increased which causes important secondary responses such as transcription factors that increase DNA and RNA activity. The creation of more ATP increases respiration that increases the production of O-2 oxidation which can be harmful if too much light is applied. Daily moderate use of light therapy induces up-regulation of antioxidants like MnSOD to counteract the harmful oxidation of O^2- in a manner much like moderate exercise. Resveratrol has a similar action via SIRT1/NAD+ –>FOX3a–>MnSOD. Like resveratrol and nicotinamide, light therapy increases NAD+ which is known to increase endurance as well as increase MnSOD. Over the short-term, heavy exercise depletes NAD+ but light exercise increases it (ref). Light therapy increases GSH (glutathione) which decreases H2O2 that is produced from the extra MnSOD that is converting O-2 to H2O2. Too much wide-spectrum infrared light, such as that received from 3 hours of bright sunlight, causes too much H2O2 which will increase MMP-1 (at least in the dermis of the skin) which some researchers think could cause photo-aging, but not cancer.

The graph below shows that wavelengths over 900 nm start to get blocked more and more by water.

The graph below shows not much light is able to pass through oxygenated blood (HbO2) when the wavelength is less than 600 nm.

Below is the same data, but INVERTED and expanded in our area of interest.

To use the absorption coefficient to find percent of light transmission through blood, use T = 2.718^(-d*A) where d is depth in cm and A is absorption coefficient. This is simple absorption equation where light scattering coefficient is not taken into account (negligible for blood). If there is scattering, replace A with SQRT(3A(A+0.8S)) where S is scattering coeff and 0.8 is anisotropy assumption.

Below is another interesting graph that shows that each mm of melanin in skin is very effective at blocking light, but that layer is very thin (less than 0.005 cm) compared to the small fiber collagen and hemoglobin in the dermis layer (0.1 cm).

930 nm and above
It appears any wavelength longer than 930 nm will start to have too much of its energy blocked by the water in tissue. See the non-ablative part of the skin section for how 1000-1500 nm can be used to burn the color out of spot and have other beneficial effects.

Laser Light verses LEDs

There has been a lot of interest and money in low laser light therapy (LLLT) for healing, but there is no reason to believe that the coherent light from a laser is any better than LEDs, sunlight, or halogen lights. Laser light does not penetrate more deeply and cells do not know the difference: all photons are the same and the benefits are based on the action of each individual photon, not on bulk properties such as all the photons having the same polarity and coherency. The word “laser” has a superior marketing appeal for companies because it sounds interesting and mysterious. It also costs a lot which means patients can’t do it on their own. These are the reasons there has been much more research in LLLT for healing than LEDs and halogens: companies and researchers have expected more profit. Light therapy is ancient and took on various new forms in the 1900′s before lasers were invented. At least since 1989 definitive statements were being made in journal articles that lasers are not needed. To quote the most recognized researcher in LLLT, Professor Tiina Karu: “An analysis of published clinical results from the point of view of various types of radiation sources does not lead to the conclusion that lasers have a higher therapeutic potential than LEDs. …The coherent properties of light are not manifested when the beam interacts with a biotissue on the molecular level….The conclusion was that under physiological conditions the absorption of low-intensity light by biological systems is of purely noncoherent (i.e., photobiological) nature….specially designed experiments at the cellular level have provided evidence that coherent and noncoherent light with the same wavelength, intensity, and irradiation time provide the same biological effect. Successful use of LEDs in many areas of clinical practice also confirms this conclusion.” (Biomedical Photonics Handbook, 2003). Thankfully, Dr. Karu is a Russian Professor so we can expect her research to be more honest and scientific compared to U.S. medical research based on corporate profit. From a journal article: “…according to all available data, does not depend on the coherence of radiation.” Reference: “Photobiological Principles of Therapeutic Applications of Laser Radiation” published by Yu. A. Vladimirov, et al in Biochemistry (Moscow) Volume 69, Number 1 / January, 2004.

Blue, Yellow, and Green

See the skin section for information about how blue can help acne (it’s really violet, near UV-A) . Blue is about 430 to 485 nm. Green is 510 to 565 nm. Yellow is 570 to 590. None of these penetrate the deeper than the skin. See the skin section for how blue can help. There are some companies that claim yellow helps remove wrinkles. I haven’t found any research that’s not funded and conducted by the people who profit from it.

Design info: Comparing LEDs

Designers trying to select LEDs or arrays will have trouble comparing LED brightness from different manufacturers. The plastic encasings can focus the light and make mcd ratings much higher, but the amount of light coming out is the same. A 100 mcd LED at +/- 10 degrees (20 degrees angle of output) has the same total amount of light output as a 2,000 mcd LED at +/- 5 degrees (10 degrees). The equation is: Milliwatt output of an LED = mcd / (683 x P) x 2 x pi x (1-cos(1/2 Angle of output)). Companies are not exactly consistent in how they measure mcd (millicandela) and the angle output. Be careful in determining if they are stating 1/2 angle or full angle. P is the “photopic response factor” ( graph ) that depends on the wavelength. mcd and P are only meaningful for visible wavelengths (not infrared). P=1 for 555 nm and P=0.061 for 660 nm. For infrared, the measurement has to be mW/SR where SR=steradians. SR units are the percentage of a sphere’s surface area, but divide SR by 4π (12.566) to get the percentage. SR is to a sphere as radians are to a circle. Replace mcd/(683 x P) with mW/SR for infrared LEDs. In practice all this is not very useful. You just have to buy the LEDs and compare them. All 850 nm LED lamps I’ve tested had the exact same efficiency. As a rough estimate, the light output energy of an LED is 30% of the input energy. Strong LEDs use 50 to 100 mA continuously. But 20 mA red LEDs can put out enough light and are very common. A good and strong 850 nm LED will use 50 mA continuously, but the device will get too hot if you pack the LEDs closely (22 LEDs per square inch for 5 mm packages) and run them anywhere near their max. 0.8 watts per square inch is the maximum energy you can apply to any device that touches skin unless a fan or heat sink is used in order to the skin temperature below 105 F (FDA guideline). Kind of like a high fever on the skin, except the blood is able to take away the heat. So at a typical spacing of 12 LEDs per in^2 (2 LED per cm^2) you can apply 66 mW per LED. That’s 45 mA at 1.55 V for the common 850 nm lamp and 35 mA at 1.9 V for a good 660 nm. LED spectrums can be generated with this spreadsheet.

Despite all the above, in directly measuring LED strength as described below, I measure only half the intensity reported by the datasheets. Datasheets report very roughly 1/3 of the energy input coming out as light output. I measure only half as much, 1/6th.

You may think the following is crazy, so let me first say the results come out EXACTLY equal to the results expected for my quality assurance check, the Sun. So here it is: it’s possible for anyone to directly measure the light intensity of something using a styrofoam cup, cocoa powder, and a home digital thermometer (accurate to 0.1 or 0.2 degrees C), based on the heat capacity of water. The equation is: mW/cm^2 = 2 cm x C x 4.18 / seconds where 2 cm is the depth of water with dark cocoa powder to make it black water, C is increase in the water’s temp, 4.18 is converting from calories to Joules, and seconds is the time the light was applied (200 seconds works best for high power device, up to 600 seconds for typical low power). The styrofoam cup needs to be cut off at 3 cm and LEDs can’t be too close because air currents cause direct heating from the LEDs. For LED devices too small to cover the surface of the water, apply the light for longer amount of time and multiply the results by the water surface area divided by the surface area of the LED array. Do not take temp measurements in the sun or while the LED device is being applied because the metal absorbs the light and heats up. Water temp must be exactly at room temperature, or more precisely, ending water temp should be above room temp by the same amount that beginning temp was below room temp. Using this direct measurement method, I typically get half of what LED manufacturer’s spec sheets say and I know for self-consistency reasons that spec sheets are wrong. To calculate sun intensity at any time at any location on a sunny day, use this spreadsheet. I originally planned to use the Sun to calibrate this device and method, but it comes out so close to the predicted value for the Sun, no calibration or correction is needed.