Whilst the potential hazards associated with optical radiation have been long understood, up until recently, consideration of this has been mainly limited to a number of specific applications using intrinsically harmful lamps, such as those emitting UV employed in tanning lamps and industrial applications, with much resting on the presumption that no hazards were posed in the majority of cases. In the absence of specific product-related standards, these measurements would have been made with reference to exposure limits published by ICNIRP/ ACGIH, following the guidance of ANSI/IESNA RP27.1-3 or CIE S009.
In the meantime, significant developments, in particular in LED technology, and their use in a wide range of applications, necessitated a particular consideration of how to evaluate the photobiological safety of these peculiar devices.
In the first instance, LEDs were treated as lasers and evaluated according to the laser standard IEC 60825, an unsatisfactory situation which did not reflect the inherent differences between lasers and LEDs. The subsequent re-arrangement of standards has given the required impetus to establish standards for the consideration of the photobiological safety of all broadband sources.
To address the issue of appropriate standards for the evaluation of LEDs, the IEC created a new standard IEC 62471:2006, adopting the text of CIE S009 (now published as a dual-logo document), and removing LEDs from the scope of IEC 60825 for all but communications applications.
IEC62471 gives guidance for evaluating the photobiological safety of electrically-powered lamps and lamps systems emitting optical radiation in the range 200-3000nm and provides exposure limits and a framework for classification.
This standard constitutes a horizontal standard, providing no product-specific safety requirements, safety measures or labelling requirements. In the absence of such, guidance is provided in IEC 62471-2.
IEC62471 has been adopted by CENELEC in Europe, due to be placed as a harmonised standard under the terms of the low voltage directive.
It follows that to CE mark a device under the terms of the LVD requires consideration of the optical radiation safety.
It should be noted that the exposure limits adopted in EN62471:2008 are not those of IEC62471:2006, but of the EU Artificial Optical Radiation Directive. At present there exists a sole discrepancy between the two, due to the adoption of current ICNIRP guidelines at the time of publishing.
Artificial Optical Radiation Directive (AORD)
In Europe, further to Article 16(1) of Directive 89/391/EEC of the 12th June 1989, introducing measures to encourage improvements in the safety and health of workers at work, the European Union has adopted a number of additional directives relating to the working environment. Amongst these are a group relating to Physical Agents, such as vibration, noise, electromagnetic fields, and artificial optical radiation.
This latter is introduced in Directive 2006/25/EC, published in the Official Journal of the European Union on the 27th April 2006, to be brought into force in law by 27th April 2010.
The measures introduced are designed to prevent harm to workers, due to exposure of the skin and eyes to coherent and non-coherent artificial sources in the work place. It is notable that solar radiation is not included in this directive. Reference is made to EN 62471 for the evaluation of non-laser sources and EN 60825 for laser sources.
IEC TR 62778
In IEC/EN 62471, the photobiological safety of lamps and luminaires intended for general lighting service (GLS) applications is evaluated by implementing the GLS classification criterion of IEC/EN62471, namely by reporting (but not necessarily measuring) at a distance at which the source produces an illuminance of 500 lux, not less than 200mm.
This situation has provided little satisfaction in the lighting industry due to differences of interpretation as to which sources should be included in the GLS category and indeed in a concern that such an evaluation may not represent a realistic exposure scenario. This has led to the publication of IEC TR 62778 "Application of IEC 62471 for the assessment of blue light hazard to light sources and luminaires", and the amendment of a range of lamp and luminaire vertical products standards harmonised to the EU Low Voltage Directive.
This approach is in keeping with the philosophy of IEC 62471 as a horizontal standard as opposed to a vertical, product-specific standard, which may include application-specific evaluation conditions and manufacturing or user safety requirements that may be needed as a result of a product being assigned to a particular risk group.
The optical radiation emitted by GLS products, broadly encompassing incandescent, fluorescent, discharge and LED sources, need not cover the entire spectral range, nor be of a level to present cause for concern. A consideration of photobiological safety depends therefore on lamp type, and is treated by technology-specific standards. Whilst the actinic UV hazard has been considered in certain such standards, and in guidance on the provision of luminaire protective shields for lamps emitting a high level of UV radiation, and the IR hazard dealt with, where required, by marking with labels warning of the presence of IR radiation, the retinal blue light hazard has not been hitherto addressed: it is on this aspect that IEC/TR 62778 has focussed.
Pertinent vertical lamp and luminaire standards include:-