Chronobiological phototherapy [from the Greek chronos = time, bios = life, fos = light, therapia = treatment] as a method of chronobiological treatment, abbreviated as ChBFT, is a properly timed application of light of appropriate intensity and spectral composition to a person for the purpose of treating depression or adjusting the sleep-wake rhythm.

Thanks to the joint efforts of chronobiologists, neurologists and psychiatrists, light therapy has become one of the accepted methods of chronobiological treatment. ChBFT brings rapid improvement (within a few days) in the condition of patients (in 50-66% of cases) with non-seasonal depressive disorder, in the depressive phase of bipolar disorder or in sleep disorder. It bridges the period of a few weeks in which the effect of pharmacotherapy takes place. In seasonal affective disorder (SAD - 'winter depression'), light has a similar effect to antidepressants. As an adjunctive treatment, ChBFT is used in patients with dementia, including Alzheimer's disease. Chronobiologists often stress the importance of being out in the sun in the morning, because intense daylight is the strongest signal to synchronise our central brain clock, which governs the sleep-wake rhythm and many processes in the body. People who are ill for long periods, bedridden or in closed wards in hospitals may suffer from a lack of light stimulus. Patients' rooms - especially in historic buildings - often have a very low daylight factor, and artificial lighting based on visual task needs represents only a fraction of the intensity needed for synchronisation. Moreover, the permeability of the eye lens to the activating blue light component decreases with increasing age. Disruption of the sleep-wake rhythm has a number of adverse consequences, not only emotional and cognitive, but also physical. The right light regime can prevent or restore the rhythm.

ChBFT methods

Bright Light Therapy (BLT) - the patient's face is illuminated for typically thirty minutes in the morning with light of approximately 10,000 lx intensity. Use: treatment of depression, treatment of SAD [1]. Afternoon exposure is used for sleep consolidation.

All-day phototherapy - a light dose of 10,000 lx for thirty minutes can be spread over a longer period of time, for example 5,000 lx for one hour or 2,000 lx for two to three hours. Use: treatment of depression, treatment of SAD, improvement of sleep rhythm.

Dawn (and dusk) simulation therapy (DDS) - the patient is gently awakened at a certain hour by light that smoothly simulates sunrise. Before falling asleep, on the other hand, the illumination decreases in the same way. The chromaticity temperature of the light may also decrease with intensity. Use: adjustment of the sleep rhythm, supplement to all-day phototherapy.

Extra-visual effects of light

Suppression of melatonin production at night - short-acting: the effect takes effect within minutes and disappears within two hours (see Figure 1). Uses: treatment of depression, facilitating awakening, postponing sleep.

Phase shift of the circadian rhythm - long-lasting: the effect is not apparent until the next day and lasts for several days. Bright light in the morning shifts the start of the day to an earlier hour. In the evening, on the other hand, it pushes back sleep and the start of the next day to a later hour (see Figure 1). Use: adjustment of sleep rhythm.

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Change in melatonin amplitude - inadequate light during the day can cause an increase in minimum daytime melatonin levels, and disturbing light at night can reduce peak levels. Uses: improving the sleep-wake rhythm by correcting light conditions.

Pupillary photoreaction - light-sensitive ganglion cells of the retina form the slow component of the photoreflex. Uses: improving depth of field.

Activation of attention - bright light and its changes increase attention and have a positive effect on cognitive processes. Uses: improving work and study results.

The extra-visual effects of light affect:

• illuminance - measured at eye level - see Figure 1;
• spectral composition - the E threshold is lower for light with a high blue component;
• exposure time (in interaction with spectrum and intensity) - subthreshold, linear (~ minutes) and saturated region (~ tens of minutes):
• the phase of the circadian rhythm (day or night time) when the light is applied;
• pupil diameter - regulation of the amount of light hitting the retina;
• Condition of the visual system - With increasing age, the lens transmits less effective radiation.

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Fig. 1 Suppression of melatonin production and phase shift of circadian rhythm in dependence on light intensity - according to [2].

Luminaires for ChBFT

In addition to the basic requirements of general lighting fixtures, phototherapy luminaires must provide the required level of illuminance, which is typically 5-10 times greater than the illuminance of the work area. The light must also have the necessary proportion of activating blue component. To make such light acceptable, high colour rendering index lamps have been used since the beginning of the research. The brightness of the illuminated area shall be as uniform as possible.

Suspended phototherapy luminaires are used in phototherapy rooms of psychiatric wards, day care centres, lounges, dining rooms, sheltered workshops and similar areas in medical or social care facilities. These are mostly luminaires providing direct and possibly indirect lighting. Illuminances range from 2500 to 5000 lx white light of cool tone 6 500 K with excellent colour rendering (Ra > 93). A typical phototherapy luminaire has dimensions of 150 × 60 cm, an input power of several hundred watts and a weight of up to 10 kg.

The relocatable phototherapy luminaires, sold under the names Light-box or solar simulator, are mainly used in the treatment of seasonal affective disorder in the home environment. They largely restrict the user's movement during the application period. An illuminance level of 10 000 l× is usually located approximately 30 cm from the luminaire. Mobile phototherapy luminaires combine the power of fixed luminaires with mobility. They require no construction or installation modifications and can be easily transported to the patient's bedside. Their disadvantage may be a higher price/performance ratio compared to fixed luminaires.

Control of phototherapy luminaires

Adherence to the schedule is crucial for chronobiological treatment. With a slight exaggeration, light heals during the day and harms at night. At least two hours before bedtime, it is essential to turn off phototherapeutic lighting. Automatic control is an advantage but not a requirement. The lights can be switched on, adjusted in intensity and switched off by the operator, for example according to a multi-point daily schedule. With automatic control, which is particularly applicable in patient rooms, the phototherapy luminaires are connected to a control unit that contains a real-time clock and provides automatic timed instructions (intensities) to the luminaires via a communication bus. The timetable is stored on a memory card and can correspond, for example, to the lighting pattern on a particular day of the year, can be adapted to the timetable of the facility or can be modified by the physician according to the needs of specific patients. This system works completely automatically and does not place any demands on the staff.

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Fig. 2 Biologically/melanopically effective spectrum according to DIN 5031-100 of 2009 and 2015.

Conclusion

Although no binding requirements have yet been directly derived from the knowledge of the extra-visual effects of light, it is advisable to consider phototherapeutic lighting already at the design stage of healthcare or social care premises or their reconstruction, and to prepare for the fact that informed clients may require such equipment to improve the quality of life of people in these facilities.

The next part of the article will be devoted to practical examples of phototherapy lighting design and control.

Graphs: author's archive, www.chbft.cz

Literature:

[1] A. Würz-Justice - F. Benedetti - M. Terman. Chronotherapeutics for Affective Disorders:

A Clinicians Manual for Light and Wake Therapy. 2nd edition, Karger, 2013.

[2] J. F. Duffy - C. A. Czeisler: Effect of Lignite on Human Circadian Physiology. Sleep Med. Online, retrieved 3/22/2016.

[3] A. Fuksa: Chronobiological phototherapy. Light, 2015, 6, pp. 42-44. Online, retrieved 22 March 2016.

Author Antonín Fuksa
Published in ERA21 2/2016