Many millennia ago, the sun was identified as a source of life, and its health benefits were realised. In the ancient world (ca. 3.000 years ago), light treatment was a part of sun cultures. Only as late as 1770 AD the healing effects of sunbathing were rediscovered and in the 19th century, this method was used to treat rachitis, joint illnesses and internal disorders. The benefits of heliotherapy are based on observations and experience. The therapeutic effects of natural and artificial radiation have only been studied systematically for a few decades, and the scientific discoveries have been used for prophylaxis, therapy and rehabilitation. Artificial light sources with corresponding spectrums were developed on that basis. Solariums are more than just cosmetically effective fashion fads.
The spectrum of electromagnetic radiation (see figure) only contains a very small component which can be perceived by the eye as visual radiation, meaning light. The adjacent spectral regions have very diverse effects on human beings (q.v. chapter "Electromagnetic safety").
Light protection is one of the most important functions of the skin for establishing its own protective mechanisms. Pigment regeneration, pigment darkening and light-induced hyperkeratosis (thickening of the horny skin layer as a protection against the penetration of radiation) are e.g. activated by solarium use – a good way to prepare before a vacation.
Vitamin D3 photosynthesis The absorption of UVB radiation through the skin promotes the generation of vitamin D3. This hormone is the prerequisite for storing calcium in the bones. It serves to prevent osteoporosis (bone loss) and osteomalacia (bone softening). Scientists today assume that many more functions in the human body are influenced and controlled by this important vitamin. Deficits during the less sunny winter months can be balanced using corresponding exposure (solarium).
Increase in performance parameters Exposure to UV "light" generally can lead to improved blood flow properties and hence improved oxygen utilisation. This leads to a normalisation of circulation characteristics such as pulse frequency, blood pressure and respiration. The result is a noticeable enhancement of performance capability.
Improved resilience In moderate doses (significantly less than required for cosmetic tanning), UVB radiation can contribute to general subjective well-being, disease prevention and strengthening of the organism. Particular immuno-oriented effects control the body’s infection defence and thus e.g. increase resistance to common colds.
Natural cosmetic for the skin Sun and solarium UV "light" does not only give the skin a pleasant, slightly tanned complexion, but can also contribute to an improvement in overall skin appearance.
UV radiation in therapy PUVA photochemotherapy, a combination of light-sensitising drugs (psoralens) and UVA exposure is used to treat psoriasis and more than 20 other indications. Other therapy treatments have been added, such as SUP (selective UV phototherapy), meaning exposure to particular UVB fluorescent lamps, however without sensitisers (drugs); and balneophototherapy, which simulates a Dead Sea climate in combination with solar UV and has led to good therapy outcomes, particularly for psoriasis and neurodermatitis symptoms. "Dead Sea" bath tubs in combination with exposure units are utilised in outpatient treatment centres as well as in home therapy applications. Diagnosing and treating atopic dermatitis (neurodermatitis) in infants and increasingly also in adults requires extensive dermatological expertise, particularly when it comes to handling optical radiation. Most patients respond well to phototherapy. Starting with treatments using the UVA spectrum of artificial light sources, the positive range of effects can later be expanded into the UVB region by adapting the patient.
Seasonal affective disorder (SAD) While the ultraviolet component of radiation is the effective component for the aforementioned applications, the visible component, meaning light, is the effective part when it comes to SAD (seasonal affective disorder). SAD, a type of depression caused by a lack of light, affects many people in the northern hemisphere during the dark season. A big percentage of these people require therapy. This requires, among other things, great illuminance values (at least 2.500 lx over ca. 2 hours) on the retina as well as flicker-free white light. Lamps and luminaires should feature as little ultraviolet and infrared (heat) radiation as possible. Therapeutic successes are verifiable, even though the modes of action have not been conclusively clarified yet. A significant factor, however, surely is the influence which the light incident on the eye has on the inner clock, as described in section .
Blue light exposure The decisive factor for the photoisometry of bilirubin (bile pigment, degradation product of haemoglobin, e.g. in the liver) is the blue spectrum between 425 nm and 460 nm, which can be generated by special emitters. Newborn babies sometimes suffer from a bilirubin level disorder, particularly jaundice, which can be successfully treated with this particular radiation therapy.
Chromotherapy The psychological effects of coloured light appeal to human emotions, but also to physiological aspects. The consideration of these aspects, besides the melanopic effects of light, is also part of "Human Centric Lighting" (see section ). Visual radiation e.g. penetrates deeper into the body than UV radiation and thus targets the vascular system in the skin. While many of these human observations are yet unexplored, positive experiences are available in the treatment of elderly people.
Photodynamic therapy As with PUVA therapy, photosensitisers as energy transmitters are the central component here. They absorb in the red region of visible radiation. Therapeutic successes have been achieved in bladder cancer treatment. Skin cancer also appears to be treatable in this fashion.
Infrared treatment The heat radiation directly adjacent to visible radiation (IR-A) can be used to alleviate or eliminate many physical ailments. This type of radiation achieves the most profound penetration into the body. It is used in IR saunas.
Therapeutic hyperthermia In therapeutic hyperthermia using the Ardenne method, the body’s core temperature is elevated without tempering the skin. It is induced by using filtered IR-A radiation emitted by quartz tube radiant heaters. This method facilitates treatment successes in cancer therapy. In many cases, chemotherapy can be supported or even replaced by this method.
Summary: The objectives in using artificial radiation in medicine are, on the one hand, the avoidance of adverse effects, and on the other hand the discovery of new applications. Possible risks must be identified and explored and thus minimised or, ideally, avoided. The advantage of artificial optical radiation modelled after daylight is its consistent availability and the possibility to optimise the radiation spectrum in terms of maximum effectiveness and dosage. As a principle, any use of radiation for therapeutic purposes requires the expertise of a physician.