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Lighting sources and technology have experienced a revolution in the last 15–20 years. Light-emitting diodes (LEDs) are now replacing compact fluorescent lamps as the main lighting sources for the illumination of industrial, commercial, and home environments. LEDs are also used in TVs, computers, smart phones, and tablets. Although the light emitted by most LEDs appears white, LEDs have peak emission in the blue light range (400-490 nm). Thus, exposure to blue light is becoming increasingly prominent in our society, and a large segment of the world population is now subjected to daily exposure (from a few minutes to several hours) of artificial blue light also at an unusual time of the day (night).

Accumulating experimental evidence has indicated that exposure to blue light can affect many physiologic functions. We now know that exposure to blue light during the day-time can provide a beneficial effect on some cognitive functions and can be used to treat circadian/sleep dysfunctions and seasonal affective disorders. However, exposure to blue light at night affects melatonin synthesis and/or circulating levels thus disrupting sleep and circadian rhythm. Disruption of circadian rhythms/sleep is now recognized as an important co-factor in the development of several pathologies (e.g., cancer, cardiovascular disease, diabetes, etc.,) and thus the exposure to blue light in the evening/night should be limited. 

It is also worth mentioning that exposure to blue light can induce photoreceptor damage. Thus, the public needs to be aware of the fact that exposure to blue light may negatively affect the retinal photoreceptors and thus vision. In this context, several studies indicate that exposure to blue light in the 470–490 nm range is considered less damaging to the eye than blue light in the 400–460 nm range. Hence the use of LEDs with an emission peak of around 470–480 nm should be preferred to LEDs that have an emission peak below 450 nm.

Finally, the use of glass with lenses that filter blue light should be also carefully considered by the public since reducing the amount of blue light during the day time may affect sleep and circadian rhythms in subjects working/living in environment that often lack a well balance illumination and in older subjects in which the yellowing of the lens is already reducing the amount of blue light reaching the retina. Conversely, the use of lenses that filter blue light may be very beneficial for people that expose themselves to LEDs in the evening/night.

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