Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

1. Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title:Optical Radiation Requirements for Light-Emitting Diodes and Implications for Visible-Light Communications Date Submitted: 18th July 2008 Source:Werner Horak, Ronald Neuhaus, and Joachim W. Walewski Company Siemens AG, Corporate Environmental Affairs & Technical Safety and Corporate Technology, Information & Communications Address Otto-Hahn-Ring 6, DE-81739 Munich, Germany Voice: +49-89-636-45850, FAX: +49-89-636-51115, E-Mail: joachim.walewski@siemens.com Re:N/A Abstract:We discuss changes in eye-safety and skin-safety requirements for light-emitting diodes due to changes in safety legislation and we discuss subsequent implications for visible-light communications. Purpose:Helping the 802.15 VLC SG to shape the scope of a VLC standard Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15. Horak et al., Siemens AG, Corporate Technology

2. Optical Radiation Requirements for Light-Emitting Diodes and Implications for Visible-Light Communications (VLC) Werner Horak and Ronald Neuhaus Siemens AGCorporate Environmental Affairs & Technical Safety Joachim W. Walewski Siemens AG Corporate Technology Information & Communications Munich, Germany Horak et al., Siemens AG, Corporate Technology

3. Executive summary • Good news: • LEDs not longer covered by laser-safety standard • Generally higher exposure limits • Already considered by manufacturer of LED • Bad news: • Wireless communications still covered by laser-safety standard • Silver lining: • LEDs in wireless communications can readily be excluded from laser-safety standard in near future Horak et al., Siemens AG, Corporate Technology

4. Outline • Historical background • Incoherent light sources • Eye-damage according to lamp standard • Skin-damage according to lamp standard • Summary and outlook Horak et al., Siemens AG, Corporate Technology

5. Historical background • 1993-2007: photo-biological safety aspects of LEDs covered by laser-safety standard IEC 60825 • Since 2007 LEDs in lighting/signalling scenarios covered by IEC 62471 (‘lamps’) • Our message: This is good for VLC • Evidence provided in the rest of this talk • But: LEDs in wireless communications still covered by laser-safety standard IEC 60825-12 (free-space optics) • Motion by Siemens at IEC TC 76 meeting in Nov 2007: Exclude LEDs from IEC 60825-12 and make IEC 62471 only pertinent standard • Status: No objections by chair Dr. Tozer • But: No action taken since then • Suggestion: Future VLC TG lobbies IEC to finalise complete withdrawal of LEDs from IEC 60825-12 Horak et al., Siemens AG, Corporate Technology

6. Salient properties of incoherent light sources • No diffraction-limited focus • Large optical extent (no point image on retina) • Intrinsic scenarios for long-term exposure (illumination, displays, …) Horak et al., Siemens AG, Corporate Technology

7. Eye-damage mechanisms for visible light • Thermal • Burning of retina • Relevant quantity at retina: Irradiance [W/m2] • Photochemical (‘blue hazard’) • Photo-induced damage of retina • Strong wavelength dependence (blue!) • Relevant quantity at retina: Radiant energy [J/m2] • Cataract • UVA (< 400 nm) • Clouding of eye lens • Exposure limit: 10 kJ/m2 over 28 800 s (350 mW/m2 on average) Horak et al., Siemens AG, Corporate Technology

8. Eye-damage mechanisms for visible light: cataract Decision: UVA not considered in this talk Level of UVA emission intimately dependent on white-light generation scheme Horak et al., Siemens AG, Corporate Technology

9. Angle of acceptance/rad Exposure duration/s Eye damage: Averaging field of view for ‘blue hazard’ • “Smearing out” of retina image due to random eye movement • Potentially lower luminenous intensity Horak et al., Siemens AG, Corporate Technology

10. Eye damage: Risk groups according to IEC 62471 • Exempt • No photo-biological risk • Critical exposure duration: 10 000 s for ‘blue’, 10 s for thermal • Low risk • “Behavioural” protection (avoiding displeasing illuminance, …) • Critical exposure duration: 100 s for ‘blue’, 10 s for thermal • Medium risk • Protection due to blinking etc. • Critical exposure duration: 0.25 s Horak et al., Siemens AG, Corporate Technology

11. Typical white LEDs used in our laboratory Ostar E3A 30 W, 2.1 rad, 150 cd, ~ 400 lm Nichia NSPW500CS: 120 mW, 260 mrad, 18 cd, ~ 1 lm Horak et al., Siemens AG, Corporate Technology

12. Eye damage (past): LED exemption limits based on laser safety standard (IEC 60825-1) Ostar E3A 30 W, 2.1 rad, 150 cd, ~ 400 lm Nichia NSPW500CS: 120 mW, 260 mrad, 18 cd, ~ 1lm Horak et al., Siemens AG, Corporate Technology

13. Comparison: exempt eye damage limits for lasers and lamps • Red LEDs: Higher limits today • Green LEDs: Mostly higher limits today • Blue and white LEDs: higher/lower limits today Horak et al., Siemens AG, Corporate Technology

14. Eye damage (today): Exempt group according to IEC 62471 Ostar E3A 30 W, 2.1 rad, 150 cd, ~ 400 lm ‘borderline’ exempt! „unreachably“ high might be reached Nichia NSPW500CS: 120 mW, 120 mrad, 18 cd, ~ 1 lm exempt! Horak et al., Siemens AG, Corporate Technology

15. Eye damage (today): Low-risk group according to IEC 62471 Ostar E3B 30 W, 2.1 rad, 150 cd, ~ 400 lm low risk Horak et al., Siemens AG, Corporate Technology

16. Conclusion regarding LED eye safety (IEC 62471) • No class ‘M’ • Main hazards: ‘Blue’ and thermal • Thermal generally not an issue • ‘Blue’ can be an issue • But: Even high-illuminance LEDs like OSTAR E3 still in low-risk group Horak et al., Siemens AG, Corporate Technology

17. Skin-damage mechanisms for visible light • Thermal • Burning of skin • 3 kW/m2 over 10 s • Corresponds to Ostar-E3A emission focused to ~ 3 cm2 • Potential issue! • Photochemical • < 400 nm (UVA): “Sunburn” (cancer!) • Critical exposure: 30 J/m2 for 28 800 s (8 h), viz. 1 mW/m2 • 350 times lower than ‘cataract’ exposure limit for eye! Horak et al., Siemens AG, Corporate Technology

18. Conclusions regarding LED skin safety (IEC 62471) • Hazards: Thermal and ‘sunburn’ • There is a class ‘M’ for skin safety • ‘Sunburn’ limits for skin automatically guarantee ‘cataract’ limits for eye Horak et al., Siemens AG, Corporate Technology

19. Overall good news • LED manufacturer will conduct classification for you! Horak et al., Siemens AG, Corporate Technology

20. Before you get too ecstatic … • Skin damage through focusing optics • Everything said only valid for single LED • Luminous intensity [cd] of closely-spaced LEDs (arrays …) potentially additive (< 100 mrad viewing angle) Horak et al., Siemens AG, Corporate Technology

21. Summary • Prospect of moving out VLC LEDs from IEC 60825-12 to IEC 62471 • Almost all LEDs either ‘exempt’ or ‘low risk’ • Red and yellow LEDs: practically all exempt • Caution: LEDs in arrays might exceed limits • Skin limits are of concern • Classification provided by LED manufacturer • Suggestion: Lobby for removal of LEDs from IEC 60825-12 Horak et al., Siemens AG, Corporate Technology

22. (Our) Vision Let’s create a safety-compliant VLC technology! Horak et al., Siemens AG, Corporate Technology

23. References /Literature • W. Halbritter, W. Horak, and J. Werner, “Measurement requirements for the characterization of photobiological hazards posed by the optical radiation of lamps or LEDs,” 2008 CIE Expert Symposium on Advances in Photometry and Colorimetry, 2008 • International Electrotechnical Commission, “Photobiological safety of lamps and lamp systems ,” IEC 62471, 2006 • International Electrotechnical Commission, “Safety of laser products - Part 1: Equipment classification and requirements,” IEC 60825-1, Ed. 2, 2007 • International Electrotechnical Commission, “Safety of laser products - Part 12: Safety of free space optical communication systems used for transmission of information ,” IEC 60825-12, 2005 • International Electrotechnical Commission, Technical Committee 76: Laser Equipment, Working Group 5: Safety of Fiber Optics Communications Systems, Unconfirmed Minutes of the meeting held in Milan, 5–9 November 2007 • W. Horak and R. Neuhaus, “Optical radiation safety analysis of LEDs on the basis of guidelines for incoherent sources,” Proc. ILSC 2005: 155-162 • W. Horak and R. Neuhaus, “Optical radiation safety requirements for LEDs according to their new status in between laser and lamp safety standards,” Proc. ILSC 2007: 49-53 Horak et al., Siemens AG, Corporate Technology