The potential risk of human exposure to optical radiation has long been researched and understood, but can LEDs cause us harm? Bryan Douglas of Lighting Council Australia explains the risk.

With the phasing out of incandescent lamps in many countries, including Australia, the introduction of new LED-based light sources sometimes raises the question of whether the spectral characteristics of LEDs are suitable to replace traditional incandescent lamps. In particular, concerns have been raised about radiation emissions from LEDs in the blue parts of the electromagnetic spectrum, giving rise to the term ‘blue light hazard’. This may be defined as the potential for retinal injury resulting from high-energy short-wavelength light – typically in the range of 400nm to 500nm.

Since LEDs are the newest lighting technology, and since some earlier products tended to have cooler (blue) colour temperatures, some people have mistakenly concluded that this technology poses an inherent blue light hazard. However the proportion of blue light produced by typical LEDs is no higher than the proportion of blue light in lamps using other technologies at the same colour temperature.

In addition, and very importantly, LEDs used for general lighting applications lack the intensity in their light output to create an optical hazard. Accordingly, in terms of their level of photobiological safety, LEDs are no different from traditional technologies such as incandescent lamps and fluorescent tubes. A comparison of LED products to the traditional products they are intended to replace reveals that the risk levels are very similar and well within the accepted safety range.

Safety Standard

At the time of preparing this article, Australia was in an advanced stage of adopting the international standard IEC 62471 Photobiological safety of lamps and lamp systems, which specifies the exposure limits for light sources (including LEDs) in the wavelength range from 200nm to 3000nm. The standard classifies light sources into risk groups 0, 1, 2 and 3 (0 equates to no risk, while 3 is high risk). The risk level is determined according to measurement criteria intended to reflect how various light sources are used in realistic applications.

One method evaluates a light source under an illuminance of 500 lux – a typical value for general lighting purposes. This 500 lux criterion is used for lamps intended for general lighting (including lamps for lighting offices, schools, homes, factories, roadways and motor vehicles). A second method measures photobiological safety from a distance of 200mm. The 200mm criterion is used for all other lamps (including, for example, lamps for such professional uses as film projection, reprographic processes, sun tanning, industrial processes, medical treatment and searchlight applications).

It is important to make such distinctions based on the application. One does not typically stare into a ceiling luminaire in an office from a distance of 200mm, but possibly in certain industrial applications workers might be required to look into light sources from a short 200mm distance – for example, during quality control processes. In such occupational cases special instructions might be needed to prevent eye damage.

After proper evaluation by either method, a light source is given a risk group (RG) classification, which indicates whether the source presents a potential exposure risk and, if so, what labelling requirements should be undertaken to alert the user.

It is important to point out that typical general illumination sources – including LEDs – pose no risk according to the standard. When these sources are used in fixtures or luminaires, the fixture or luminaire would also typically pose no risk.

Taking the 500 lux criterion as the measurement basis, typical consumer LED products do not fall into risk group 2, which is the first cautionary risk group. This was also confirmed by a study of the French agency for food, environmental and occupational health & safety (ANSES) in a 2010 study which found that even high-output discrete LEDs are classified into risk groups 0 or 1.

Natural aversion reflex

Nevertheless, looking straight into the bright, point-like light sources (including LEDs, but also other strong point-like light sources, such as clear filament or discharge lamps) should be avoided. Fortunately, when people happen to look into a bright light source accidentally a natural aversion reflex occurs: they instinctively close their eyes or look away from the source. People are very familiar with this reflex when they accidentally look at the sun. Hence the natural aversion reflex helps protect our eyes from bright light sources.

Blue light and children

The lens of a child’s eye filters blue light less effectively than an adult’s lens. Children are thus more sensitive to blue light hazard. However the LEDs typically used in homes, offices, schools and retail outlets, as mentioned above, do not produce intense levels of blue light and are therefore not hazardous, even for children. Since such applications have a low surface brightness (intensity), even ‘pure’ blue light is harmless, regardless of whether the blue light is produced by LEDs or other common light sources.

People with high sensitivity to blue light

The above statements are valid for healthy people. People who have been medically diagnosed with highly sensitive skin or eyes to blue light, such as lupus (a tiny proportion of the general population), may be wise to consider installing specialised lighting in their homes that do not emit light in the blue part of the spectrum.

Biological importance of blue light

Blue light exposure is important to the welfare of human beings. Blue light with a peak around 460nm to 480nm regulates the biological clock, alertness and metabolic processes. In natural conditions, outdoor daylight synchronizes the biological clock (called the circadian cycle). However in today’s society, many people spend most of the day indoors and may lack the blue light exposure that was common in the past. It thus follows that blue and cool white light sources can be used to create lighting conditions such that people will receive their daily portion of blue light to keep their physiology in tune with the natural day-night rhythm. Research is currently underway that will allow us to take full advantage of blue light from artificial light sources.

Conclusion

LEDs pose no greater optical hazard than other common artificial light sources. The proportion of blue light produced by typical LEDs is no higher than the proportion of blue light in lamps using other technologies at the same colour temperature. Moreover, current generation LEDs used for general lighting applications lack the intensity in their light output to create an optical hazard.

As a way of ensuring the photobiological safety of lighting into the future, Australia is adopting an international standard which categorises light sources according to their risk profiles. Current generation LEDs used for general illumination fall into the lowest risk categories of 0 or 1.

In principle, the eye has an aversion response so one would never fix an LED enough to do direct damage, but cumulative exposure should be taken into account. There are no acute concerns for damage by LEDs, but it is clear that looking directly at LEDs can momentarily impair vision and that should be taken into consideration, especially when electricians are working on a ladder, roof etc. Do not stare at LEDs; power off before working in proximity.