Light is the most valuable gift of nature to living beings. In fact, life has evolved under the influence of light and is a stimulus for the living organisms to grow. Without light, not only would we be bereft of enjoying all the wonders of nature, but we would also find it impossible to have an existence in this world.
However, sometimes even this most valuable gift may threaten to impair our vision. As explained by Dr. Aashish K. Bansal, the harmful effects of light on the eye can be due to either chronic or acute exposure. While the sun and fire are natural sources of light, man has also been able to create or produce light artificially by means of incandescent lamps and/or fluorescent lamps. And some of these natural and artificial types of light pose a threat to our eyes if proper precautions are not observed. To understand the way our eyes interact with light, it’s essential to have a basic understanding of the types of light.
Types of light
The sunlight or the natural light consists of visible spectrum, ultraviolet light and infrared spectrum. The visible light consists of wave lengths of 400 to 750 nm and includes the colors violet, indigo, blue, green, yellow, orange and red. The UV spectrum further consists of UV-A (320- 400 nm), UV-B (290-320nm) and UV-C (200-290 nm). The infra-red spectrum consists of wavelengths greater than 750 nm.
Out of all these spectra, visible spectrum and infra-red components don’t have much harmful effects. However, it is the ultraviolet component which has both specific good effects and specific harmful effects on the eyes. Particularly, UV-B and UV–C are very harmful for the eye. Luckily, most of UV-C spectrum is absorbed by the atmosphere and doesn’t reach the eye, and the eye itself absorbs part of the UV-B spectrum.
The incandescent light mainly consists of visible spectrum, mainly toward the red side and infra-red rays. This light is produced as a result of heating the filament. The other and the more popular artificial source of light is fluorescent lamp. Its spectrum contains very high amounts of UV rays, and the light produced from it is called cold light. It also gives more brightness than the incandescent light; however, it can still give only about 10 per cent of the brightness given by sunlight.
Effects of light on eyes
While light is an absolute necessity for us and its significance in our life is obvious, being the instrument of vision and also having a role in the synthesis of Vitamin D in our body, it can have its share of ill effects on our eyes. The harmful effects of light on the eye can be considered in two situations; in normal circumstance due to chronic exposure, and in abnormal circumstances due to acute exposure.
- Chronic exposure: It has been seen that people who spend more time in the sun, either because of the nature of their profession or hobbies or any other reason, develop cataract at a much younger age than the rest of the people. Similarly, these people are also more prone to develop fleshy growth on the eye surface called as pterygium. Macular degeneration is another very serious vision impairing problem that occurs due to chronic exposure of UV-B and blue wavelength of light.
- Acute exposure: Ordinary sunlight, when reinforced by reflection of light from surfaces like snow or sea or desert can lead to severe damage to the corneal surface by the UV rays, and results in the person developing acute redness, watering, photophobia and ulcers on the cornea surface. This is known as snow blindness. Similarly, if one looks directly into the sun for even a fraction of a second, it can lead to burning or damage to the macula, the area where the image forms in the eye. This typically happens in situations like a solar eclipse, as in normal condition it is impossible to look at the sun directly. The same thing can happen if one happens to look at a source of strong light like a welder’s arc.
Apart from these serious conditions, minor problems like glare and sensitivity to light or ocular fatigue can occur on prolonged viewing of LED or computer screens etc. or with improper lighting at the work place. Another peculiar effect of light on our body is regulation of various biological rhythmic activities like sleep, hunger, physical fitness, sexual function and hormone secretions. All these activities get synchronized with the 24 hour day and night cycle, and annual cycle of change in day lengths. So, any disturbance or change in our exposure to the day and night cycle leads to behavioral changes, sleep disturbance, hunger disturbances etc., as typically happens in jet lag or in cases where the person is not exposed to natural light for many weeks or months.
Protective measures for the eyes
- Always wear UV blocking sunglasses when out in the sun.
- Always use UV blocking sunglasses whenever holidaying on the beach or skiing or in deserts. Remember, all sunglasses are not UV–blocking.
- Never look at a solar eclipse without proper UV protecting glasses.
- Never look in the direction of a welding arc.
- Never stay confined indoors for days together. It is good to get exposure to natural light for some time every day, like a morning walk or an outdoor sport. Similarly, always switch off the lights and draw curtains while sleeping. That way the dark and light cycle will keep your biorhythms well-tuned.
- Whenever working on a computer screen or watching TV, take breaks in between for a few minutes after every half an hour and look away from the screen.
- Use anti-glare glasses while working on computer or while driving at night.
- There should be uniform lighting at your work place. An illumination of about 500 lux is sufficient for work stations and offices.
- No bright light should fall on the computer screen directly. Allow natural light to come into your homes and offices, as much as possible.
- Use fluorescent lamps with double protection film.