Photobiological Safety of Lamp Systems

A consideration of the possible dangers to the human body due to exposure to optical radiation has, in the past, been restricted to those established through experience to be the most hazardous, lasers and sources of ultraviolet (UV). The publication in 2006 of IEC 62471:2006 "Photobiological Safety of Lamps and Lamp Systems", indicated a new framework for the assessment of the photobiological safety of non-laser electrically-powered products discharging light in the spectral region 200-3000 nm.

Adopting the current CIE S009/E-2002 guidelines to publish IEC62471:2006, the scope of this standard is to offer guidance for the assessment of the photobiological safety of lamps and lamps systems, excluding lasers, discharging light in the spectral region 200-3000 nm. A measurement methodology and exposure limit values (taken from ICNIRP data) are given in the consideration of the six dangers to the eye and skin for an exposure duration of up to eight hours, taken as a working day. No consideration is taken of the probable effects of long-term exposure, abnormal photosensitivity, nor abnormal behavior.

Hazard Wavelength Range (nm) Skin* Eye*
Actinic UV 200-400 Erythema
Elastosis
Photokeratitis
Cataractogenesis
Near UV 315-400 - Cataractogenesis
Retinal Blue Light 300-700 - Photoretinitis
Retinal Thermal 380-1400 - Retinal burn
Infrared Radiation 780-3000 - Corneal burn
Cataractogenesis
Thermal 380-3000 Skin burn -

*Principle Bioeffects

A four tier-classification structure, based on permissible exposure time before surpassing the EL of each hazard, is defined, ranging from “Exempt” to “Risk Group (RG)” 3. In the case of retinal dangers, the aversion response time of the eye is taken into consideration.

Risk Group Philosophical Basis
Exempt No photobiological hazard
RG1 No photobiological hazard under normal behavioral limitation
RG2 Does not pose a hazard due to aversion response to bright light or thermal discomfort
RG3 Hazardous even for momentary exposure

The assessment consists of an intricate series of measurements of spectral irradiance (200-3000 nm) in consideration of dangers to the skin and front surfaces of the eye, and spectral radiance (300-1400 nm) in consideration of hazards to the retina which is fundamentally protected outside this range because of the transmission features of the lens. Measurements are performed in specific geometrical conditions which replicate biophysical phenomenon, such as the effect of eye movements on retinal irradiance.

Hazard Wavelength
Range (nm) Spectral Weighting Function
Actinic UV 200-400
Near UV 315-400
IR Radiation Eye 780-3000
Thermal Skin 380-3000
Blue Light Small Source 300-700
Blue Light 300-700
Retinal Thermal 380-1400
Retinal Thermal Weak Visual 780-1400

 

Photobiological Safety of Lamp Systems

Although irradiance accounts for light arriving at a surface from the whole hemisphere above, because of its position with respect to the bridge and nose, the eye is shielded from wide-angle radiation. Within the scope of this standard, the measurement of irradiance in all but the case of the thermal skin risk is performed over a 1.4 radian acceptance angle: light discharged from a source outside this acceptance angle need not be measured.

In consideration of dangers to the retina, consideration is made of the eye movement to account for the impact on retinal irradiance.

Photobiological Safety of Lamp Systems

For momentary viewing, the retinal image of a source subtends the same angle as does the source, the smallest image created on the retina, according to IEC62471, having an angular extent of 1.7 mrad, given the imperfect imaging performance of the eye. With increasing exposure time, because of eye movement (saccades) and task-determined movement, the retinal image is “smeared” over a larger area of the retina, causing a corresponding decrease in retinal irradiance. A time dependent function is defined to signify the spread of the retinal image, ranging from 1.7 to 100 mrad, from 0.25 s (aversion response time) to 10000s exposure.

In the context of the photobiological safety, the measurement of radiance is performed in a manner that reflects this occurrence, the FOV of measurement being selected to account for the light falling within a particular area of the retina. The measurement FOV follows thus the same time dependence, from 1.7 to 100 mrad, irrespective of the size of the source measured. The measured quantity is more accurately termed spatially averaged radiance. Where the FV extends beyond the angle subtended by the source, the result is an average of the true source radiance and the “dark” background. Additionally, since the angular subtense of a source varies with distance, spatially averaged radiance differs with measurement distance.

Photobiological Safety of Lamp Systems

The distance at which a source should be assessed depends upon its envisioned application to allow consideration in a likely exposure scenario, taken generally as general lighting service (GLS) and all other applications (non-GLS).

The present definition of GLS is vague, but relates to finished products meant for illuminating spaces which discharge “white” light. Assessment should be reported, not essentially measured, at a distance at which the source creates an illuminance of 500 lux, which distance may be less than a meter for household luminaires, but many meters for street lighting for instance. While irradiance measurements may be done at a convenient distance and scaled to 500 lux, physiological radiance, reliant on the source subtense with regard to the applicable FOV, should be performed at the precise distance. The assessment of photobiological safety in lighting applications has essentially been substituted by an approach presented by IEC TC 34.

Non-GLS sources should be measured at a distance of 200 mm from the (apparent) source, which distance signifies the near point of the human eye: closer than 200 mm, the retinal image is out of focus, resulting in lower retinal irradiance. Here, the concept of apparent source is vital. Where a lens is used to collimate the output of an LED, a magnified virtual image is created behind the chip. It is relating to this apparent source that the 200 mm measurement distance should be taken as it is this which the eye images.

Although the measurement at 200 mm may signify a worst-case exposure condition for the retina, it is not the case for the skin and front surfaces of eye where the exposure distance may be closer. This latter prospect has not yet been taken into consideration in this standard for which the main concern is acute retinal damage.

Risk group dependent emission limit values can be computed from the ELVs and the risk group time basis are provided in terms of radiant flux for thermal dangers or energy (radiant flux times time) for photochemical dangers: a measured irradiance result can be directly compared with the previous, and an exposure time acquired for the latter. This procedure does not relate to the measurement of radiance for which the FOV of measurement is time reliant.

A pass/fail test is thus applied to the retinal dangers based on measurements at FOVs corresponding to the least exposure times of the classification system in turn, beginning from the exempt risk group. Where the resultant radiance surpasses the highest permissible radiance for a given risk group, the next risk group is analyzed. The comprehensive evaluation of retinal dangers is rather more convoluted since source size and level of visual stimulus should be taken into consideration in establishing which ELVs to apply.

Classification

As defined in part 1, a classification system, based on the least exposure time before the ELV is surpassed, is defined ranging from exempt (no risk) to risk group 3 (RG3) (high risk), from which the limit irradiance (radiance) of each risk group may be established, and against which the measured irradiance (radiance) may be compared.

Labeling

IEC62471 is intended as a horizontal standard, and as such does not include manufacturing or user safety needs that may be required as a result of a product being assigned to a specific risk group. Such safety necessities differ according to application, and should be dealt with in vertical, product standards. IEC TR 62471-2, however, does provide some additional guidance on the measurement and offers a recommendation of labeling for each hazard and risk group.

Labeling

Photobiological Implementation of IEC62471 in Europe

In the European Union, CE marking demonstrates product safety by compliance with the relevant applicable EU directive, such as the low voltage directive (LVD), via application of European Norme (EN) standards harmonized to the directive under consideration. Although compliance with these EN standards is not compulsory, it does provide presumption of compliance with the vital health and safety requirements of the instruction considered.

Optical radiation is definitely considered under the terms of the LVD, appropriate to electrical products operating at voltages of 50-1000V AC, and to which EN62471:2008, the European adoption of IEC62471, is harmonized. From 1st September 2011, assessment of LEDs against the laser standard ceases to allow presumption of conformity with the vital health and safety requirements of the LVD.

From April 2010, the EU artificial optical radiation directive (AORD), 2006/25/EC, came into force, accepting exposure limits somewhat different to those of IEC62471. For steadiness, EN62471 adopts the exposure limits of the AORD and is the standard to be used to assess worker exposure to non-laser sources of optical radiation.

Applicable also to LEDs is the EU Toy Safety directive to which is harmonized EN62115 “Safety of electric toys”. Although this standard has in the past referenced the laser standard, EN60825 for the classification of LEDs, it is presently under review but it is estimated that reference will be made to EN 62471 where measurements are necessary.

Finally where products are not encompassed by the LVD or toy directives, consideration should also be made of the basic product safety directive to which few standards are specially harmonized, yet for the assessment of non-laser sources of light, EN62471 is the applicable EN standard.

Implementation of IEC62471 in ROW

Although many global standardization bodies are thinking about the adoption of IEC62471, few have yet issued national standards let alone a legal structure to render testing compulsory. Of the activity seen, much is linked to the lighting industry, for which a distinct standardization framework is in place and under active progress to include solid state lighting.

To the knowledge of the author, China is now alone in having formally implemented a voluntary standard, GB/T 20145-2006, with Japan anticipated to publish JIS C 7550 in November 2011.  While certain countries, such as New Zealand and Australia, are presently working on the adoption of IEC62471 as a voluntary standard, some others (Hong Kong, Republic of Korea) are currently content to reference IEC62471 on a voluntary basis. Canada is at the stage of considering implementation and possible regulations.

Finally, in the USA, where ANSI RP27.1 exists as a voluntary standard, there is presently no mandatory obligation for the assessment of non-laser sources. Following a meeting in August 2011, however, of the standards technical panel of UL/ANSI 8750 “Light Emitting Diode (LED) Equipment for Use in Lighting Products”, a task team has been set up to consider the employment of photobiological safety standards for those lighting products enclosed within this UL standard.

This information has been sourced, reviewed and adapted from materials provided by Bentham Instruments Limited.

For more information on this source, please visit Bentham Instruments Limited.

Citations

Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Bentham Instruments Limited. (2019, January 10). Photobiological Safety of Lamp Systems. AZoM. Retrieved on December 05, 2019 from https://www.azom.com/article.aspx?ArticleID=14809.

  • MLA

    Bentham Instruments Limited. "Photobiological Safety of Lamp Systems". AZoM. 05 December 2019. <https://www.azom.com/article.aspx?ArticleID=14809>.

  • Chicago

    Bentham Instruments Limited. "Photobiological Safety of Lamp Systems". AZoM. https://www.azom.com/article.aspx?ArticleID=14809. (accessed December 05, 2019).

  • Harvard

    Bentham Instruments Limited. 2019. Photobiological Safety of Lamp Systems. AZoM, viewed 05 December 2019, https://www.azom.com/article.aspx?ArticleID=14809.

Tell Us What You Think

Do you have a review, update or anything you would like to add to this article?

Leave your feedback
Submit