What came first: the chicken or the egg? In the technical files the answer is quite simple: first comes the product, then the standard. Since 1993, when Nichia did introduce in the market the Blue LED (based on GaN), the photo biological safety was taken into account and International Electrotechnical Commission IEC decided to include LED in the category of LASER product and related norm (IEC 60825). Such a decision was based on the use of Infra Red LED in the fiber communication system due to their very narrow band.
Few years later – 1996 – the American Association (IESNA) did publish the norm ANSI / IESNA RP27.1 “Photobiological safety for lamps and lamp systems – general requirements” announcing some norms for sources other than LASER.
In 2002, the International Commission on Illumination adopt the main part of the ANSI / IESNA RP27.1 as a base for a new norm S009/E-2002: “Photobiological safety of lamps and lamp systems;” four years later the fast improvement and diffusion of LEDs in other fields led the IEC to draft the 60825, a very severe Norm for “general purpose” LED. From now on, LEDs are no longer considered as a LASER equivalent source.
Along 2006 IEC did adopt the guidelines specified in S009/E-2002 joint with IEC 62471:2006 “Photobiological safety of lamps and lamp systems;” two years later the European edition of EN 62471 has been published. It gives guidance for evaluating the photobiological safety of lamps and lamp systems including luminaires. It specifies the exposure limits, reference measurement technique and classification scheme for the evaluation and control of photobiological hazards from all electrically powered incoherent broadband sources of optical radiation, including LEDs but excluding lasers, in the wavelength range from 200 nm through 3000 nm. In particular, some limit values are specified based on six risk categories for human skin and eyes up to 8 hours of exposition, considered as a standard working time.
Photobiological safety of lamps: EN 62471
The light radiation can cause damage to the skin and eyes. Not only does the LED light but any light source can cause damage. European legislation obliges the manufacturer to perform laboratory tests and writing on the lamp the risk category (if present). More, the emission limits shall not be exceeded. Test to run, risk classes and emission limits are defined in EN 62471. The tests and emission limits are not easy to understand – because they require specific technical knowledge and just experts and equipped laboratories can analyse the hazard of the lamps. What we can do is to understand the hazard of the various classes and if there are “risk free” lamps.
The potential damage of the light varies with the radiation wavelength and with the quantity received.
The quantity is given by the power for the exposure time. An intense radiation requires less time to cause damage of a lesser intensity.
We clarify the concept with an example: you can get sunburned if exposed one hour on July 21 at noon – while it will be required over 8 hours in a day in of March.
The EN 62471 defines the absolute limits of exposure to the surface of the skin and the cornea
The radiance and irradiance measurements are carried out at the distance at which it produces an illuminance of 500 lux and to not less than 200 mm in the case of general lighting devices and 200 mm for all others.
EN 62471 defines the following the exposure limits for the different groups…
Lamps belonging to Group 3 cannot be used for general lighting.
According to the typical spectral emission just few lamps can be dangerous:
In these cases, the lamps must bear on the packaging the risk group.
With regard to the blue light, whereas the values stated above, it is possible to define a value of the illumination (at the level of the eyes) in function of the colour temperature (CCT) of the lamp, under which the exposure is equal to or less than the group 1:
In the chart above a higher colour temperature (CCT) is related to a higher power in the blue wavelength. In other words, the risk can be simply checked by a measurement of illuminance with a cheap and easy to use instrument: a lux meter.
Electric Engineer, Italy
Visitor Professor at
Madrid University (Spain)