Light therapy
Generalities
Light is essential for our health and well-being, but today’s lifestyles often keep us from benefiting from the natural light of the sun. Bringing us the light we need to us is the alternative offered by light therapy.
Light therapy is a medical treatment that consists of exposing the eyes to light of a specific intensity and visible spectrum that is close to sunlight every day for a given length of time depending on the indication. The beneficial effect of light is linked to its physiological action particularly its influence on secretion of melatonin, the “sleep hormone,” and serotonin, a neurotransmitter.
Physiological effect of light :
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Light inhibits secretion of melatonin (sleep hormone), which makes it easier to wake up in the morning, and promotes alertness throughout the day.
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Light stimulates the area at the base of the brain and increases the level of serotonin, which has an antidepressant and appetite-regulating effect.
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Light influences the biological clock, leading to sounder sleep and more vital energy.
The light we need :
The light used in light therapy, called bright light, must have a intensity of at least 2000 lux to produce the beneficial effects on mood, increased energy, and sounder sleep.
Light therapy is most effective when the wavelength of the emitted light is about 460 nm (nanometers), or blue light. However, simultaneous emission of white light protects the eye’s reflex by contraction of the pupil.
Exposure duration and distance :
A relationship between the length of exposure to a light source and the intensity of the light has been demonstrated in seasonal depression where a 10,000 lux dose of white light for 30 minutes has a similar effect to a dose of 2500 lux for 2 hours. Blue light, since it has a narrower wavelength, is more effective and requires a lesser intensity. 2500 lux for 20-30 min is enough.
Light intensity decreases in proportion to the square of the distance between the transmitting source and the reception area of the transmitted beam, so that the ideally the device would have a source with a fixed position, close to the target. Thus the idea of a product worn on the head is a testament to its effectiveness.
The time of exposure :
Whether in the daytime or at night, the time when exposure to a strong light takes place also plays an important role. Light application at midday has little effect, while an evening application, over the next few days, delays the time of the body’s maximum temperature and the time a person falls asleep, so that someone on this schedule will spontaneously go to sleep at a later time. It delays his or her “falling-asleep phase.”
On the other hand, an early morning application has the reverse effect over the next few days, bringing forward the time of peak body temperature and the onset of sleep that evening. So, with this schedule, the tendency is to go to sleep earlier and get up at dawn the following morning. Here we speak of a “phase advance.” This influence of the time the light is applied has come to be called the “phase response curve.”
Light where it’s needed :
The light transmitted by a light therapy lamp enters the eye, and passes through the pupil to illuminate the retina.
The part of the retina that is richest in receptors is the lower part.
Chief indications for light therapy
Light therapy is indicated for treating all pathologies in which disturbance of circadian rhythm is suspected (i.e., the 24-hour biological rhythm).
1. Seasonal affective disorder
Contraindications and principles of light therapy precautions
Provided the whole light spectrum is used, excluding infrared and the entire ultraviolet region, the drawbacks of light therapy appear to be insignificant. Thus far, systematic ophthalmological studies have not identified any drawbacks at all.
Light therapy may cause excitation, and this is probably the most serious acknowledged effect. Depressive patients may go from depression to a hypomanic or manic state. Temporary headache, some nausea, and a feeling of eye tension have been described. In these cases, the effects are mild and transient.
In people who are ill, the only contraindications to phototherapy are manic status and eye lesions, particularly those of the retina (here, a prior eye examination is recommended).
