Characteristics of application and its use
In the past two decades, there have been significant improvements in the lifetime, efficiency and range of optical radiation emissions of light-emitting diodes (LEDs). There are now LEDs available with peak wavelength emission from the short wavelength UV range, e.g. 214 nm, out to 4.3 µm (4300 nm). Their application depends on wavelength.
The discovery of high efficiency narrowband blue LEDs and their combination with a phosphor to produce white light has led to their widespread use as a source for general illumination/lighting. Other approaches are also being used, such as the combination of red, green and blue emitter chips in LEDs to produce white light. These new sources are replacing traditional light sources like incandescent and fluorescent lamps. However, there are small differences in the light output of white LEDs compared to traditional lighting sources. Although white LEDs do not generally emit any ultraviolet radiation and very little infrared radiation, they may emit more blue radiation than traditional white light sources. Therefore, the use of LEDs with higher levels of blue light has caused some concern for the effects of this exposure on human health.
Optical radiation effects on the body and health implications of exposure to such radiation from LEDs
High levels of blue light have been shown to be potentially hazardous to the human retina, leading to possible temporary or permanent loss in vision. Under extreme exposure conditions, acute damage has been produced to the retina of humans or animals by blue light. Acute retinal injury (photomaculopathy) is extremely rare since an individual must overcome their natural aversion response to bright light and stare for minutes at a light source, such as the sun or an arc lamp. Therefore, under typical exposure conditions, no damage to the human retina from the blue component of the white light from LEDs is expected. In addition, concern has been expressed that chronic exposure to intense sunlight could contribute to age-related macular degeneration (AMD). This is based on a handful of studies showing increased incidence of AMD in populations with significant chronic solar exposure. However, at this time, there is no evidence to indicate that chronic exposure to the light from white LEDs will lead to increased incidence of AMD. Further research is needed on this subject.
Exposure to blue light at night has also been shown to disrupt the human circadian rhythm. Thus, the replacement of traditional street lamps with white LEDs has led to concern about related long-term adverse health effects, such as chronic disruption in sleep. However, most people do not get exposed to the direct light from street lamps. These effects might also be caused by increased use in the evening/nighttime of devices like cell phones or tablets, which use LEDs for illumination, especially if the daytime exposure to light is low.
Another concern about the increased use of LEDs is their ability to produce flicker or glare. The flicker from LEDs has been shown to produce headaches, migraines and other non-specific adverse health effects in a small proportion of the population. This effect mostly occurs with LEDs connected to drive circuits that do not eliminate the mains power frequencies (strictly twice the mains frequency) or are connected to incompatible dimmer circuits. It is technically straightforward to solve these problems so changes to the input circuit can eliminate flicker. Glare, which is caused by poor lighting design that allows for direct viewing of the LED chip, without sufficient diffusion, can also cause visual discomfort or disability. Glare can be reduced by proper light source design and installation.
With regards to eye safety, i.e. prevention of acute damage to the retina, exposure to the light from white LEDs is safe under reasonably foreseeable use. Exposure to UV LEDs should be treated with the same precautions as exposure to traditional UV lamps since exposure to UV radiation (especially UVB and UVC) can cause skin or eye damage without the normal aversion responses associated with bright (i.e. visible) light. To date, IR LEDs are not thought to be sufficiently powerful to cause adverse health effects.
Regarding disruption of the human circadian rhythm, we are still learning about this complex issue and ICNIRP is working on a related Statement to be published in the near future. In the meantime, as a precautionary measure, ICNIRP recommends that exposure in the evening or nighttime to light sources that are rich in blue light be avoided.
If one experiences episodes of headaches or other unusual symptoms after traditional lamps are replaced with LEDs, the possibility of improving the circuitry driving the LEDs should be explored.