There is a wide range of LED and SLD (Super Luminescent Diodes) products that were created for the same applications as therapy lasers. These products may improve some conditions but they will never produce the level of results that you get from a real therapy laser. Some the manufacturers even have laser in their name yet they use 90% LED technology. Please make sure you check the specs on any product before you buy it and remember that LEDs only delivery a small portion of the energy into the tissue when compared to a true laser.

A light-emitting diode (LED) is a semiconductor light source with properties between an incandescent light bulb and laser. When an LED is switched on, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. The color of the light defines the properties of the light and the corresponding energy of the photons. Early LEDs emitted low-intensity red light (610-760nm) , but modern versions are available in a wider variety of wavelengths including the infrared wavelengths required for deep tissue penetration (the therapeutic window). LED light is non-Coherent (radiating in all directions) and divergent. Typical LEDs are designed to operate with 30-60 milliwatts [mW] of electrical power. LEDs can be switched fast but they can not be super-pulsed. The vast majority of devices containing LEDs are classified as Class 1 LED products but LEDs can fall under the same limitation of LASERs if the power density is high enough. Here we see an image from Wikipedia showing that the actual output of a red LED ranges from 600 to almost 700nm.

LED output


Super Luminescent Diode (SLDs) are similar to LEDs, however they have the potential to be brighter.

LASER (Light Amplification by Stimulated Emission of Radiation) is a mechanism for emitting electromagnetic radiation via the process of stimulated emission. Cold Laser light is:

  • Monochromatic in a wavelength that allows for the best penetration into tissue
  • Spatially coherent: This means the energy is not destroying itself because different parts of the wave are out of phase.
  • Controlled-divergence beam : Unlike hot lasers that have almost no divergence, cold lasers use optics to diverge the beam by up to 30 percent. This allows cold lasers to push more energy into the direction that is needed.
  • Optically manipulated to maximize penetration.

In laser technology, "coherent light" denotes a light that is spatially constant waves of identical frequency and phase. The waves of photons are non-interfering. When interfering, two waves can add together to create a larger wave (constructive interference) or subtract from each other to create a smaller wave (destructive interference), depending on their relative phase. Two waves are said to be coherent if they have a constant relative phase. The laser's beam of coherent light differentiates it from light sources that emits incoherent light beams, of random phase varying with time and position. Laser light is generally a narrow-wavelength electromagnetic spectrum monochromatic light. LASERs can be pulsed (turned on and off quickly). Pulsing a LASER can allow what would normally be a class 4 laser to be qualified as a class 1 or 2 laser. Like with other electrical transmission equipment (cell phones, walkie talkies, etc) , power is somewhat proportional to range (or depth in the case of cold laser therapy).

Comparing LEDs and LASERs
So what is the difference between the light created by an LED and the light created by a LASER. The light from the LED is non-coherent and divergent. The divergence of the LED light wastes energy and may require special optics to focus the available energy into the desired areas. The second limitation, coherence, can not be corrected.


400 nM and Up

narrow band

400 nM and Up


Low - Divergence
No, may require special optics to correct. Wastes energy.
Yes, Perfect for targeting specific areas.
Can Be Super-Pulsed
Yes, making them safer
No, Random destructive and constructive interference may produce random results
Efficiency at delivering energy into the tissue About 5% About 90%


Lets look at an example to illustrate the difference in the ability of an LED or SLD to deliver energy when compared to a true laser. If you take a 100 watt LED light and stand about 20 feet way on a sunny day, you might not be able tell if the LED is turned on or off. That is because so much of the energy is lost in divergence, non-coherence and the output is distributed over a wider width of wavelengths. If you stand 20 feet away from a 100-watt coherent monochromatic non-divergent laser and look right at it, you might look like this.

laser hole in head

OK, the image is a bit silly but at that distance a laser can still cut through steel. Lasers put all the power where they are aimed. LEDs and SLD lose the majority of their energy.

The final answer is that both LEDs and LASERs can be used in cold lasers. LEDs are primairly used for superficial treatment, due to the basic properties of the LED. Although LEDs may have the correct wavelength, the controlled stimulation of deep tissues requires a coherent and focused beam of photons. The biggest problem is that LEDs are not efficient at getting the energy all going into the tissue. The efficiency (tissue energy/ output energy) is about 5% so you need a 15 to 20 watt LED to get the same tissue energy level as a 1-watt laser.

Also, LEDs cannot be pulsed so they cannot take advantage of using a higher power pulsed emitter which is both safe and powerfully (greater transmission distances). Because LEDs are just so cheap (often pennies a piece) , they are still widely used in cold lasers to target superficial areas. The combination of both LASERs and LEDs deliver photons to both the superficial and the deep tissue.

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