The light we see comes from can only come from two sources, the sun or artificial light, such as from a light bulb. Therefore, today we will explain the risks of artificial light on the eyes. Visible light is between 400 and 700nm and is only part of the entire electromagnetic spectrum.

Artificial light damage to the eyes

The most important damage that incident light can produce on our eyes is located in the retina. The possible damage that can be caused by light between 400nm and 1400nm can be classified into three types.

Structural damages: Mainly caused by certain laser radiation.

thermal damage: Caused by brief exposures (seconds or even less) that produce an increase in tissue temperature of 10º to 20ºC above ambient temperature.

Photochemical damage: Caused primarily by shorter wavelength radiation at intensity levels too small to cause thermal damage. It can occur when there is a longer exposure time and low intensity, making the temperature increase negligible. It is very dependent on the wavelength since it increases a lot in the blue zone of the spectrum.

Photochemical damage to the eyes

It has been seen that photochemical damage can be the cause of some retinopathies associated with sun exposure in very bright environments, such as skiing or sailing or flying planes. This had already been described in different studies years ago and for this reason caution and adequate protection are recommended in certain situations of greater risk.

Eye injuries by light

There are conflicting opinions about the relationship between exposure to short-wavelength visible light and ultraviolet radiation and eye damage in humans.

On the one hand, epidemiological evidence is sometimes insufficient or considered limited. On the other hand, we found studies carried out in the laboratory that document the injuries induced by radiation and that indicate that the potential of ultraviolet radiation and light of short wavelength can not be left aside. It is possible that this difference of opinion is justified by a great variability of conditions that separate the laboratory study and the epidemiological evidence, with factors that influence such as exposure conditions, lifestyle, nutrition or genetic background.

Risks of light on the retina

Many laboratory experiments carried out with animals aim to find the causes of age-related macular degeneration and various studies have agreed that blue light (which we find in both natural and artificial light) can be harmful to the retina.

On the other hand, blue light is also fundamental in the visual process and in other important physiological aspects such as circadian rhythms. All species on the planet present a large number of biological cycles that repeat approximately every 24 hours, known as circadian rhythms and maintain an important relationship with the internal clock of the brain. Some examples may be the replenishment of DNA in individual cells or the sleep / wake cycle.

The first stimulus received by the human circadian system and that of many other mammals is that formed by incident light on the retina. It seems that the main photoreceptors found at the beginning of this circuit have their maximum spectral sensitivity at λ=460-480nm (blue/cyan).

Effects of light on the eyes at night

It has been seen in studies that exposure to light at night, without respecting a time of darkness, especially if the light is rich in blue, suppresses melatonin secretion. This hormone influences physiological aspects such as regulating the sleep/wake cycle, and plays a significant role in the immune system.

At the other end of this relationship between blue light and different physiological functions, we can hear or read proposals for therapies and treatments based on exposure to blue light to improve depressive symptoms and even sleep problems.

In low light conditions (scotopic conditions) the rods are the most sensitive to light and are the ones that we mainly use in night vision of humans. The fact that this type of photoreceptors are more sensitive to blue wavelengths, and the fact that the objective pursued is to be able to see in these conditions, has led us to the belief that outdoor lighting should use high-brightness lights in blue.

Despite this, uncertainty still exists in mesopic lighting conditions or in real situations, since many aspects influence it, such as the pupil diameter of each person, sudden changes in lighting or adaptation time.

Conclusions of the effects of blue light on the eyes

There is a direct and necessary relationship between circadian rhythms and different physiological functions, both positively and negatively if there is overexposure

Advantages of blue light

1. Better sensitivity of the rods in scotopic conditions, therefore, better visibility at night.
2. Controversial epidemiological evidence

Disadvantages of blue light

1. More adaptation time needed when changing from photopic to scotopic vision.
2. Possible retinal toxicity in laboratory studies.