Low level light therapy may facilitate several important non-thermal effects that facilitate healing, pain management and other therapeutic goals.







Properties of LASER
Coherence
Collimation
Monochromaticity





Electrical Energy —> Lasing Medium—> Electron Excitation to Higher Energy Level—> Electron Return—>Energy Release (photon)










Spontaneous/Stimulated Emission by Radiation



A photon is a basic unit of electromagnetic energy. Radio waves and microwaves infrared and ultraviolet light X-rays and gamma rays: All of these are light, and all of them are made up of photons. Photons are at work all around you. They travel through connected fibers to deliver internet, cable and cell phone signals.





When an atom absorbs or loses energy an electron may be excited, meaning it is “pushed” into a higher energy level.

Spontaneous emission is an energy conversion process in which an excited electron or molecule decays to an available lower energy level and in the process gives off a photon.


This process occurs naturally and does not involve interaction of other photons. The average time for decay by spontaneous emission is called the spontaneous emission lifetime.


For some excited energy levels this spontaneous decay occurs on average within nanoseconds while in other materials it occurs within a few seconds.

This process can occur in isolated atoms,compounds, molecules, and other types of materials, and it can occur in solids, liquids, and gases.


Energy is conserved when the electron decays to the lower level, and that energy must go somewhere. The energy may be converted to heat, mechanical vibrations, or electromagnetic photons.

If it is converted to photons, the process is called spontaneous emission, and the energy of the photon produced is equal to the energy difference between the electron energy levels involved. The emitted photon may have any direction, phase, and electromagnetic polarization.


There are many ways in which an electron can be excited to a higher energy level . Spontaneous emission processes may be classified based on the source of energy which excites the electrons.

If the initial source of energy for spontaneous emission is supplied optically, the process is called photoluminescence. Glow in the dark materials emit light by this process.

If the initial form of energy is supplied by a chemical reaction, the process is called chemiluminescence. Glow sticks produce spontaneous emission by chemiluminescence.


If the initial form of energy is supplied by a voltage, the process is called electroluminescence. LEDs emit light by electroluminescence.


If the initial form of energy is caused by sound waves, the process is called sonoluminescence.


If the initial form of energy is due to accelerated electrons hitting a target, this process is called cathodoluminescence.


If spontaneous emission occurs in a living organism, such a firefly, the process is called bioluminescence.



Light by Stimulated Emission





Stimulated emission is the process in which an excited electron or molecule interacts with a photon, decays to an available lower energy level, and in the process gives off a photon.


If an incoming photon, with energy equal to the difference between allowed energy levels, interacts with an electron in an excited state, stimulated emission can occur.


The energy of the excited electron will be converted to the energy of a photon.


The stimulated photon will have the same frequency, direction, phase, and electromagnetic polarization as the incoming photon which initiated the process.


The emitted photons may stimulate further emissions from excited atoms of the same type.


Stimulated emission is rare as normally the majority of electrons are in a resting state.


To increase the likelihood of stimulated emission there must be population inversion.


This is a state when photons have a higher probability of encountering excited electrons and stimulating further emissions of photons with the same energy.

An external source of energy must be used to increase the proportion of excited atoms in the population to a level where stimulated emission is a frequent occurrence. This process is called pumping.


Therefore a laser device consists of a:


pumping system

lasing medium

optical cavity


The pumping system or the external source of energy creates a population inversion for the excited electrons in the laser chamber.


The lasing medium or gain is the source of laser radiation and supplies the electrons needed for the stimulated emission of radiation.

The wavelength of the emitted light is determined by the distinctive energy transitions of the molecules of the medium.


The optical cavity is a chamber consisting of two parallel mirrors enclosing the laser medium which is excited by the pumping system.

Photons of energy in the axis of the chamber are reflected off the mirrors at either end, stimulating further emissions in the same axis.


One mirror in the chamber is partially reflective, and this allows some of the stored photons to escape and form a laser beam.





The medium dependent laser wavelength is a primary factor that determines its depth of penetration into biological tissue. Longer wavelengths generally penetrate deeper than shorter wavelengths, although other factors like tissue type, absorption coefficient, and scattering also play significant roles.


The depth of penetration is the distance at which the laser's intensity drops to approximately 37% of its surface value.



Depth of Penetration



An "LLLT grid" refers to a physical or conceptual grid used in low-level light therapy (LLLT) to ensure consistent and precise application of light to a specific area. It functions by dividing the treatment zone into a grid of squares or marked sites, allowing the therapist to apply the laser or light at specific intervals and for a consistent duration at each point.

Grid Method


Physical grid: A pre-made grid made of fabric with marked holes is placed over the treatment area to guide the applicator.


Conceptual grid: The treatment area is mentally or physically divided into squares of a specific size, such as \(1\) square cm.


Consistent application: The light is applied to each square or hole for a set amount of time, ensuring that every part of the area receives the same dose.


Precision: Using a grid helps ensure the applicator is perpendicular to the target tissue and that there is proper spacing between treatment sites, which is crucial for effective treatment.




The most common lasing media in Low-Level Laser Therapy (LLLT) are semiconductor lasers, particularly GaAlAs (Gallium Aluminum Arsenide), and gas lasers like HeNe (Helium-Neon). These are used to produce red and near-infrared light, which is absorbed by the body for cellular stimulation.

Semiconductor diodes are also widely used, with other media like argon and GaAs (Gallium Arsenide) also being common.


Common LLLT Lasing Media

Gallium Aluminum Arsenide (GaAlAs): A type of semiconductor laser that can be customized to specific wavelengths by adjusting the ratio of gallium to aluminum.


Helium-Neon (HeNe): A gas laser that is commonly used, often at a wavelength of 633 nm. Superficial tissues 1-2 mm deep rapidly directly absorb energy produced with this laser and 8-10 mm indirectly.


Gallium Arsenide (GaAs): Another type of semiconductor laser used, with a common wavelength around 904 nm. Tissue 1-2 cm. rapidly absorbed within the energy produced with this laser and up to 5 cm indirectly.


For surface-level benefits like skin rejuvenation and healing, wavelengths between 630–660 nm are ideal.

For deeper issues like muscle pain, inflammation, and deeper tissue repair, near-infrared (NIR) light at 810–850 nm is more effective because it penetrates deeper into the body.


Indirect effect from energy absorption is a lessened response that occurs in deeper tissues. The normal metabolic processes in the deeper tissues are catalyzed from the energy absorption in the superficial structures to produce the indirect effect.













The photobiostimulatory effects of LLLT occur at the cellular and molecular levels making direct assessment of efficacy difficulty. However, physical therapist assistants must remain focused on the easier assessed therapeutic goals!



In understanding the effects of LLLT physical therapist assistants must rely on their previously mastered concepts in human anatomy and physiology. Below are three descriptions of how LLLT effects may be therapeutic.

Mitochondrial Chromophore Stimulation

As you likely remember the mitochondrion is a crucial membraned organelle largely responsible for the production of ATP. Chromophores are photosensitive molecules embedded within mitochondrial and cellular plasma membranes. They are sensitive to different wavelengths of light produced by LLLT and their stimulation enhances ATP synthesis, mRNA production, and osteoblastic proliferation. All of these may enhance tissue healing capabilities.


Increased levels of nitric oxide and histamine

Nitric oxide and histamine are powerful vasodilators. Increased vasodilation may decrease tissue ischemia, increase perfusion, and thereby bring more nutrients to an area and facilitate the removal of wastes, also facilitating healing capabilities.


Decreased prostaglandin E2 levels

As you may recall, prostaglandins are important molecules found within cells and play crucial roles in the inflammatory response and stimulating nocioceptors. For example, non-steroidal anti-inflammatory drugs such as Advil inhibit prostaglandin production with a result of limiting pain.




As the research continues to evolve, clinical indications for the use of LLLT grow. Physical therapy clinicians must be cautious in how and when LLLT is used.


Some documented indications include:

FDA-Approved For:


Minor muscle and joint pain


Arthritis and muscle spasms


Joint stiffness


Relaxation of muscle tissue


Increasing local blood circulation


Other Common Applications Include:


General acute & chronic pain


Reduction of inflammation


Back pain


Fibromyalgia


Wound healing


Carpal tunnel


Sports injuries




Remember, both you and the patient must wear the manufacturer prescribed protective goggles.