The use of light as a therapeutic agent can be traced back over thousands of years. Indeed, the sun has been an omnipotent, almighty deity throughout the world since the start of human history. From the time of the Pharaohs, most ancient civilisation and cultures have worshipped the sun or sun gods and made some connection between sunlight and health. The ancient people prayed to the sun god for everything, and disease was no exception; as such, light therapy (phototherapy) began as sun worship. According to McDonagh (2001), the use of sunbaths by the ancient Romans and Greeks for maintaining general health and for therapeutic purposes is particularly well documented [1-3].

Light therapy is also called heliotherapy, named after Helios, the sun god of the ancient Greeks. Although beginning as sun worship, it is now an accepted scientific treatment as a result of clinical studies and advances in photophysics, photochemistry, and photobiology. Currently, light therapy is one of the most important therapeutic modalities in dermatology, some allergen-induced inflammatory diseases such as allergic rhinitis (hay fever), and a variety of psychological diseases [1, 4].

Major physiological processes in the brain and body are switched on and off by the presence or absence of natural or artificial light. Biochemical processes triggered by light include the production of vitamin D, the inhibition of melatonin (a hormone that affects mood), and the stimulation of serotonin and norepinephrine (brain chemicals that influence mental alertness and well-being). Light-sensitive cells in the eyes called photoreceptors convert sunlight into electrochemical impulses, which are transmitted through the optic nerve to brain centers that affect vision and activate the endocrine system. Many functions necessary for growth and well being - breathing, sleeping, blood pressure, body temperature, appetite, moods, mental acuity, and the immune system - are governed by the endocrine system and hence are affected by natural light.

There is also evidence suggesting that proper quantities of visually perceived light are needed for healthy functioning of the cerebral cortex, the part of the brain that controls motivation, learning, and creativity; the limbic system, the part of the brain that stores emotional impressions of the world; and the motor cortex and the brain stem, the parts of the brain that coordinate body movement and the maintenance of life.

Light therapy (phototherapy) is the use of light for the treatment and prevention of disease. Strictly speaking, it refers to the use of visible light, infrared or ultraviolet light lying outside the visible region of the spectrum; although laser therapy and photochemotherapy may also be classified as light therapy. One might ask what the fuss is about light therapy. For starters, light therapy is becoming increasingly popular in the treatment of a variety of diseases ranging from dermatological diseases to psychological diseases. Its versatility is impressive and it seems that a lot more is being regularly discovered about its therapeutic effects. The secret to the numerous ways in which light can be used in medicine lies in the varying wavelengths of different colours of light.

Full spectrum light consists of two parts: visible and invisible. The visible part consists of all the colours of natural sunlight, which are essentially the colours of the rainbow. In relation to light therapy however, red and blue visible light are the most popular; green and yellow visible light have also been implicated in the light therapy treatment of certain conditions (particularly acne vulgaris).

(Taken from http://electronics.howstuffworks.com/nightvision1.htm)

The invisible wavelengths on the other hand are at each end of the visible colour spectrum as indicated above. At the red end is the infrared wavelength (heat) and at the violet end is ultraviolet.

Ultraviolet light exists just below violet on the spectrum and has three wavelength designations: UVA (near-UV with wavelength between 320 and 400nm), UVB (mid-UV with wavelength between 280 and 320nm), and UVC (far-UV with wavelength between 100 and 280nm). UVA is mainly responsible for tanning; UVB aids in the stimulation of the production of Vitamin D3 in the skin and is also essential for the absorption of calcium into bones. UVC is typically used in hospitals to kill bacteria and viruses; however it is considered to increase the risk of cancer. Both UVA and UVB radiation are components of sunlight.
Note: The sun also gives off UV-C; however most of it is blocked by the ozone layer. Overexposure to the sun has been known to increase one's chances of developing skin cancer. Fortunately, the chances of developing skin cancer can be reduced by regular, moderate exposure to the sun.
UV light works by inducing biologic reactions in the skin's cells, which decrease the number of skin cells that grow too quickly and kills T cells in the skin, resulting in the clearing of psoriatic lesions. The therapeutic effect of UV light is mostly attributed to its immunosuppressive and immunomodulant (modification of immune response or the functioning of the immune system) action.

UVA Light
UVA light is usually offered in conjunction with a photosensitiser called psoralen, a procedure referred to as photochemotherapy. Photosensitisers can be applied directly to the skin or taken orally so as to make the skin more sensitive to ultraviolet light. Photochemotherapy is used for more severe cases of skin diseases, which fail to respond to topical therapy. PUVA (Psoralen with Ultraviolet A) is a form of photochemotherapy, which involves topical or oral administration of psoralen followed by exposure to varying doses of UVA light. The combination of psoralen and UVA works by slowing down the rapid growth of skin cells and killing T cells in the skin. It is effective in approximately 80% to 90% of cases that are resistant to other treatments or that cover large areas of the body. The use of drugs and the higher risk of adverse reactions, including the risk of skin cancer, have generally limited PUVA therapy to patients with severe skin conditions.

UVB Light
UVB light can be categorized as broadband and narrowband. This refers to the range of wavelengths included in the UV light source.

The broadband devices deliver full spectrum UVB light whilst the narrow band devices deliver a very narrow range of the UV light spectrum, focusing on the specific wavelengths most effective for the treatment of disease. Broadband UVB therapy has been around for more than 80 years and is still highly effective. Its biggest drawbacks however is the frequent visits (3 to 5 times per week) patients have to make to the site which offers the treatment and the fact that broadband light does not reach the scalp and areas where skin folds occurs.

Narrowband UVB light can be delivered with either a light bulb or with a hand held laser device and is proving to be more effective than the traditional broadband therapy as it clears psoriasis faster and produces longer remissions. It may also be effective with fewer treatments per week than broadband UVB. Like broadband UVB, it is still not known if narrowband UVB therapy poses a long-term risk for the development of skin cancer.

UVB treatment is typically offered using a light "booth" or "light box" several times a week for as long as the condition persists, which may be for the lifetime of the patient. In most cases a patient must go to a doctor's office or other facility for treatments. However, UVB treatment is available for home use under certain circumstances and under strict physician supervision.

Benefits of UV light
1. UV light is an effective treatment for psoriasis. It has been reported that the condition of 80% of psoriasis sufferers improves when they are exposed to UV
2. UV light is also an effective treatment for many other diseases, including asthma.
3. UV light activates the synthesis of vitamin D, a prerequisite for the absorption of calcium and other minerals from the diet.
4. UV light increases the level of sex hormones. According to findings, it has been shown that estrogen has a sharp peak of absorption in a portion of the UVB range (~290nm). This indicates that estrogen is most efficient when a woman is exposed to UV wavelengths.
5. UV light increases the efficiency of the heart. Out of 20 people exposed to UV light in study, 18 of the people tested had an increased cardiac output (average of 39%). In order words, their hearts became stronger and pumped more blood.
6. UV light lowers blood pressure. This was noted in a study carried out in which some individuals were exposed to UV light once. A dramatic lowering of elevated blood pressure was noticed, an effect which lasted from 5 to 6 days.
7. UV light reduces cholesterol. This fact was established in an experiment where patients with hypertension and related circulatory problems were exposed to UV light. 97% of these patients had almost a 13% decrease in serum cholesterol levels 2 hours after the first exposure. In addition, 86% of patients within the same group maintained the same serum cholesterol level 24 hours later.
Other types of fat implicated in heart disease are also reduced by exposure to UV radiation, an occurrence which may be due to the fact that the body requires UV light to help break down cholesterol.
8. UV light assists in weight loss. It is thought that this is caused by the fact that UV stimulates the thyroid gland, which increases metabolism and consequently the burning up of calories.
(Taken from Light Therapy Canada; http://www.lighttherapycanada.biz/uv.htm)

Side effects of PUVA
The most common side effects of PUVA include nausea, itching and redness of the skin.

Long term risk of this mode of treatment is a higher risk of skin cancer, particularly non-aggressive forms such as squamous cell carcinoma and basal cell carcinoma. Studies have shown that the more PUVA treatments a patient has, the more at risk they are at developing skin cancers when compared with the general population who have not had PUVA treatment.

There is also an increased risk of developing freckles and/or experiencing premature aging of the skin. This may occur in PUVA patients who have received more than 150 treatments within 5 years.

If the eyes are not protected for 12 to 24 hours after a PUVA treatment, cataracts can be induced. This is due to the fact that psoralen remains in the eye lens for a period of time following ingestion of the drug. No increased incidence of cataracts have however been noted in patients using the proper eye protection. Special UVA blocking PUVA glasses are usually prescribed for use following treatment and these must be worn for at least 12 hours after ingestion of psoralen wherever the sun shines (even if indoors!). If sunglasses are to be used, they must be able to filter out 100% of UV light.

Side effects of UVB treatment
Short term risks of using UVB treatment are minimal and may include irritation and sunburn. These risks can however be resolved by reducing the amount of UVB administered.

Long term risks include skin cancer and skin aging. However, long term studies involving a large number of patients treated with UVB have failed to demonstrate an increased risk of skin cancer. Hence, UVB treatments are considered to be one of the most effective therapies for moderate to severe psoriasis with the least amount of risk.

Infrared light is just below red visible light on the electromagnetic spectrum (infra is a Latin word meaning "below"). It has wavelengths between 750nm and 1mm and can penetrate to a depth of 30-40mm, making it more effective for bones, joints, deep muscle, and so on. It has continuously been tested by NASA's space medicine program and is being used in a variety of treatments. Infrared light has wavelengths ranging from far-infrared (this is thermal and is experienced as heat), mid-infrared, and near-infrared (closest to visible light). Of these three, near infrared wavelengths are typically used as a mode of light therapy.

Infrared light increases energy inside cells by stimulating cytochromes (proteins important in cell respiration) which are part of the process (electron transportation chain), which converts sugar into energy. This stimulates cellular reproduction, relaxes muscles and stimulates nerve transmission. It also enhances immune response, reduces scar tissue and promotes wound healing. Not only that, infrared light is able to stimulate collagen production thereby making skin tighter, it increases blood capillary circulation and vascular activity, increases RNA and DNA synthesis, stimulates production of the adrenals which reduces pain and stimulates the production of adenosine triphosphate (ATP) an immediate energy source for muscle contraction.

Near-infrared light
Near-infrared light is light with a wavelength from 700 to 1300nm. The long wavelengths of near infrared light, next to red on the spectrum and invisible to the human eye, can penetrate deeply into human tissue. For that reason, it may be the light treatment with the most dramatic potential for revolutionizing medicine.

Benefits of Infrared Light Therapy
1. It promotes healing, raises white blood cell counts, and improves cell growth as well as DNA synthesis and protein synthesis in cells.
2. It increases circulation by increasing the formation of new capillaries, which are additional blood vessels that replace damaged ones. New capillaries speed up the healing process by carrying more oxygen as well as more nutrients needed for healing and they can also carry more waste products away.
3. It aids in stimulating the production of collagen, which is the most common protein found in the body. Collagen is the essential protein used to repair damaged tissue and to replace old tissue. It is the substance that holds cells together and has a high degree of elasticity. By increasing collagen production less scar tissue is formed at the damaged site.
4. It improves skin conditions (including cellulite) and serves as an all-around beauty treatment.
5. It helps to accelerate metabolism, thereby preventing or slowing down the aging process as well as discomposing and discharging surplus to stay slim.
6. It provides deep, infrared heat that can penetrate far below the surface of the skin to produce a soothing, comforting effect on the nerves and subcutaneous fat associated with aging.
7. It promotes blood circulation, eases chronic inflammatory diseases, such as rheumatism, eliminates soreness & pain, fatigue and stress, and also relieves all forms of arthritis and carpal tunnel syndrome.
8. It helps sports-related and musculoskeletal injuries such as repetitive strain injury or bursitis.
9. Clinical benefits include pain relief in conditions such as carpal tunnel syndrome (CTS), bursitis, tendonitis (elbow, shoulder or knee), ankle sprain, neck and shoulder pain, arthritis, sciatica, as well as tissue repair in cases of diabetic ulcer, venous ulcer, bedsore, mouth ulcer, fractures, tendon rupture, ligamentous tear, torn cartilage, and nerve injury.
10. It helps with hypertension, arteriosclerosis, and coronary artery disease by dilating arteries, blood vessels, and tiny capillaries.
11. It stimulates metabolism, thereby promoting the elimination of toxins that accumulate in cells (i.e., poisons, carcinogenic heavy metals, toxic substances from food processing, lactic acid, free fatty acids, and uric acids).
12. It also stimulates tissue granulation and connective tissue projections, which are part of the healing process of wounds, ulcers or inflamed tissue.

Red light occurs within the visible light spectrum. Although it does not penetrate as deep as near infrared, red light seems to help wounds heal more quickly. At a wavelength of 660nm, it penetrates tissue to a depth of 8-10mm and is beneficial in the treatment of problems close to the surface of the skin such as wounds, cuts, and scars, and is particularly effective in treating infections. It can also be used to remove precancerous skin cells without scarring.

Red light, when used in conjunction with near infrared, has the ability to reverse aging. The light promotes collagen formation, which aids in smoothing out wrinkled skin. It also has anti-inflammatory effects and can kill bacteria.

Light therapy with visible light has been shown to have a beneficial effect on acne vulgaris with an added advantage of avoiding the potential long term risk of UV radiation. Blue light in particular has been implicated in the light therapy treatment of acne vulgaris. It is on one of the latest types of light therapy that is widely used to treat skin problems. The blue light emitted targets P. acnes, the bacteria which causes acne. Once the skin is exposed to a certain wavelength of blue light, the bacteria is targeted and killed, leading to a clear out of skin pores and consequently acne is eliminated.

Apart from its use in the treatment of acne vulgaris and as an antibacterial agent, blue light has the ability to reset the biological clock. It is suggested that "blue light boxes" are far more effective than full spectrum sunlight boxes, having equal intensity, at fighting seasonal affective disorder (SAD). Studies have also indicated that a dose of blue light, depending on when it is given, can increase alertness or help fight insomnia.

Combination Blue and Red Light
By combining antibacterial and anti-inflammatory actions, blue and red light can act synergistically in improving various forms of acne, making it an effective and safe treatment for acne vulgaris.

The table below gives a brief quick-glance summary of the types of light used in light therapy.

Near Infra-red light	Red light	Blue light	Ultraviolet light
Long wavelengths penetrate deeply into human tissue	Does not penetrate deeply as near infra-red	Used as an antibacterial agent	Used to keep bacteria and viruses from reproducing
Invisible to the human eye	Aids in wound healing and removal of cancerous cells without scarring	Has a special ability to reset the biological clock	UV light in vents used for air sterilisation
Light treatment known with most dramatic potential	Ability to reverse ageing	Used to fight SAD	Used in water treatment plants
Used to treat severe mucositis (side effect of chemotherapy and radiotherapy)	Promotes collagen formation – smooth out wrinkled skin	Can increase alertness and combat insomnia (given under controlled conditions)
Shown to reduce heart attack severity by 50% and repair cardiac tissue	Has an anti-inflammatory effect and can kill bacteria	Exposure to blue light in the evenings makes Alzheimer's patients more likely to sleep through the night (Figueiro's studies)
	Used in conjunction with near infra-red light and blue light to treat severe cases of acne

The word 'laser' stands for Light Amplification by the Stimulated Emission of Radiation. Lasers emit high intensity light, which is usually of a single wavelength (monochromatic). The light beam waves are in phase (coherent) and travel in parallel (collimated). Because it is coherent, laser light can be focused to a very small spot maintaining a very high irradiance. The light produced by a laser is produced within an optical cavity containing a medium, which could be a gas, liquid or solid. Lasers are named according to the medium stimulated to produce light and this determines the characteristics of the light emitted. Laser light is delivered as a continuous, pulsed or pseudo-continuous beam. The wavelengths of lasers typically used in dermatology are in the UV, visible and infrared range.

In recent times, UV lasers have become available and have applications in the treatment of dermatological diseases such as psoriasis and vitiligo. It has been demonstrated that the most efficient therapeutic wavelengths for the treatment of psoriasis are within the UVB spectrum and 311nm narrowband UVB have become popularised for this treatment over the last decade. Acne vulgaris, which has always been treated by exposure to blue, red, violet, or UV light has more recently been treated with diode lasers, which are used to target sebaceous glands. Significant reduction of acne lesions have been demonstrated on the back after 4 treatments with a 1450 nm diode laser. Although this is a promising preliminary result, future clinical trials are ongoing to determine the actual efficacy, longevity, and cost-effectiveness of this treatment. Laser therapy can also be used in the treatment of vascular lesions, hypertrophic scars and keloids (developed as an abnormal response to cutaneous injury and characterised by an overabundance of collagen), facial wrinkles, scars and sun-damaged skin (by laser resurfacing), hair removal and for the treatment of hair loss.

Low Laser Therapy is used to ameliorate hair loss and it is thought to work by supplying energy to the body in the form of non-thermal photons of light. In the right application, it is thought that the body absorbs the energy supplied on a cellular level, converting light energy to chemical energy, which the body uses to accelerate the normal healing rate of tissue. Visible red light at a wavelength of about 660nm penetrates tissue to a depth of about 8 to 10 mm such that the entire hair organ is covered to a depth beyond the hair bulb. Laser light increases blood flow to the hair follicle up to 50%; this causes more nutrition to be supplied to the hair and consequently increasing the growth rates of the hair.

Photodynamic Therapy
Photodynamic Therapy (PDT) is a form of light therapy and is based on the principle that certain compounds can be activated by particular wavelengths of light (often from a laser) to induce cytotoxic effects in the tissue where they are located. It is a developing technique, which can potentially destroy unwanted tissue whilst sparing normal tissue. PDT has been used to treat a variety of skin cancers, non-malignant lesions, inflammatory diseases, and hirsutism. Treatment is such that a photosensitiser is first administered to the patient (usually by injection) after which laser light is directed onto the tissue containing the drug. This activates the drug and consequently the unwanted tissue (precisely where the light has been directed) is rapidly destroyed. Many light sources and delivery systems have been used including nonlaser devices.

Benefits of laser therapy
Laser therapy,
1. Stimulates fibroblast development and accelerates collagen synthesis in damaged tissue, leading to faster wound healing.
2. Reduces the formation of scar tissue following tissue damage from cuts, scratches, burns or post surgery.
3. Induces temporary vasodilation increasing blood flow to damaged areas.
4. Reduces swelling caused by bruising or inflammation of joints to give enhanced joint mobility.
5. Accelerates cellular reproduction and growth.

1. It is a non-invasive method that can kill acne-causing bacteria. Bacteria can be destroyed when the light penetrates their cell walls, inhibiting the growth for further acne causing cells.

2. Lack of light can cause depression in the winter season. Light therapy treats depression disorders by giving various amounts of light which manipulates the brain to address these seasonal changes. This prevents patients from taking anti-depressant drugs which are know to cause side effects.

3. Our sleep habits are governed by light and light therapy exploits this known fact by giving patients varying amounts of light at designated times of the day because light therapy can work into the body's sleep rhythm or circadian rhythm. This prevents patients from taking tranquilizers for ease of sleep. It is also used by frequent travelers to alleviate the frustrations and pain caused by jet lag.

4. Skin conditions such as psoriasis and eczema can be treated by light therapy at a much faster pace than other therapeutics. Ointments, shampoos and antibiotics need months or years to fully take effect.

5. Accredited salons for UV light therapy provide excellent and safe methods for self tanning. Given at safe doses, UV light can give you the tan that you want without concerns of overexposure to sunlight's harmful rays.

6. Light therapy has shown to rejuvenate cells and gives more youthful and glowing appearance. This cost effective way means less expenditure on expensive cream treatments and elixirs.

7. Light therapy has shown to largely benefit over 90% of patients.

8. Its ease of use makes it more consumable and it can be used at home with special light boxes.

9. Under correct supervision or appropriate knowledge and usage, light therapy can be controlled and its effects monitored accordingly. So the amount of light, its intensity and frequency is measurable and adjusted very easily.

10. Light therapy is safe and the most convenient therapy known, developed in the present day. Its ongoing research exceeds its reliability thus creating assurance for patients and professionals. If placed under the control and correct supervision it can be beneficial for its purpose with explicit results.

Skin related conditions
1. Acne vulgaris
Sunlight was previously known to improve acne conditions in many hypersensitive individuals which were thought to be due to antibacterial and other effects of the UV spectrum. But it is prevented for long term usage due to potential risks of skin damage and cancer.

Blue and red light therapy seems to be the most effective treatment for acne by reducing the number of spots by three quarters. Some acne does clear up significantly when exposed to UV light, but this is unsuitable as a long-term remedy because of the increased risk of skin cancer. A mixture of blue and red light wavelengths produced by a light box has been shown to be very effective in reducing the number of visible spots on affected areas.

Home use light boxes usually work well and are effective for people with long-term acne. They are also likely to be cheaper than dermatologist office light treatments, and can be repeated over several years for negligible cost, as opposed to once weekly or fortnightly.

2. Psoriasis
Psoriasis involves the excessively fast turnover of skin layers. Application of UV radiation to the skin slows down this rapid growth of skin cells, resulting in marked improvements of the condition. Light therapy for skin conditions like psoriasis or even eczema use UVA (320-400nm waveband) or UVB (280-320nm waveband) light waves. PUVA treatment (UVA combined with orally taken psoralen) is often times used for the treatment of psoriasis. Narrow Band UVB is the 310nm wave length and is given as a light therapy treatment rather than full spectrum UVB.

3. Skin aging
Red light at 660nm induces energy levels of cells by activation of ATP in skin cells increasing the rate of production of collagen for a few days, giving a lifting effect. No permanent improvement of skin aging has been demonstrated, but completion of the healing of skin damage does seem to proceed faster.

4. Wound healing and neuropathy
Monochromic infrared light at 890nm has shown effective results through clinical studies to help restore sensation and pain reduction in patients with neuropathy and to improve circulation which ultimately increases the healing rate of non-healing ulcers. This works by the release of Nitric Oxide into the bloodstream by infrared light which aids in increasing local circulation and improvement of blood flow.

5. Premenstrual Dysphoric Disorder (PMDD)
Women's menstrual cycle is regulated by light and darkness as well as by hormones, and circumstances that upset the body clock, such as changing regular sleeping and waking patterns, jet lag, and shift work, may upset their menstrual cycle. Each month, women report symptoms such as fluid retention, weight gain, bloating, breast tenderness, poor sleep, irritability, blue moods, and other symptoms in the 3 to 5 days before their periods start, and for the first day or two of menstruation. The combination of emotional and physical symptoms is referred to as Premenstrual Dysphoric Disorder (PMDD) or Premenstrual Syndrome. Light therapy is able to promote strong daily rhythms, and can in this way assist in regulating the menstrual cycle.

Mood and Sleep related
1. Seasonal Affective Disorder (SAD)
SAD is a type of winter depression that affects approximately half a million people every winter between the months of September and April, in particular December, January and February. This disorder is caused by a biochemical imbalance in the hypothalamus due to shortened daylight hours and the lack of sunlight in the winter. For many, this is a seriously disabling neurological and psychological problem, preventing individuals from functioning normally without continuous medical treatment. For others, this condition is a mild but debilitating condition causing discomfort which is not considered as severe suffering.

Light therapy was first used to treat those with Seasonal Affective Disorder, or seasonal depression. In these cases, lack of light in the winter months, particularly in the north, contributed to depressive symptoms in many individuals. Full sunlight is preferred for SAD whereas other treatments are based upon infrared light exposure and a number of product options for the emission of this light are available which include light boxes. These products utilise high and intense artificial illumination that are effective for this disorder providing 10,000 lux or more directed angularly at the user's eyes simultaneously filtering out any harmful UV radiation. Modern light boxes are beneficial as they do not emit UV radiation thus reducing damaging effects. There are two major modes of light therapy for SAD, bright light therapy and dawn stimulation (although this will not treat the main symptoms of SAD, such as depression).

2. Non-seasonal depression
It has been proven that the use of light therapy for patients suffering from depression is as effective as it is for those suffering from SAD. A recent trial concluded that the benefits of light therapy were felt after only one week, whereas many medications took up to 8 weeks for the benefits to be felt. Also, using light therapy together with medication has superior results to either treatment on its own.

3. Delayed sleep phase syndrome
The timing of light exposure is a crucial step when treating this syndrome, light must be provided as soon after arising as possible to achieve any effect at all. Some users have responded with lights that turn on shortly before waking (dawn stimulation).

4. Postnatal depression
Many women suffer from depression during and after their pregnancies, maybe as many as 1 in 10. Studies are being conducted to show whether light therapy is useful in treating these depressed episodes, and early indications show that it is.

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