LEDs
A light-emitting diode or 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 30â??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 some limitation of LASERs if the power density is high enough. LEDs can

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

  • Spatially coherent,
  • Narrow low-divergence beam,
  • Can be optically manipulated with lenses.

 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 laserâ??s beam of coherent light differentiates it from light sources that emit 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.

LED
Laser
WaveLength
400 nM and Up
400 nM and Up
Low - Divergence
 No, may require special optic to correct. Wastes energy.
 Yes, Perfect for targeting specific areas.
Can Be Super-Pulsed
No
 Yes, making them safer and more effective.
Coherent
 No, Random destructive and constructive interference may produce random results
Yes

The final answer is that both LEDs and LASERs can be used in cold lasers. Because of the basic properties of the LED, they are primarily use for superficial treatment . Although LEDs may have the correct wavelength and some may have enough power, the controlled stimulation of deep tissues requires a coherent and focused beam of photons. Also, LEDs can not be pulsed so they can not 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.