Doc.: IEEE 802.15-08-0523-04-0vlc Submission to IEEE 802.15 SG VLC 17th July 2008 Horak et al., Siemens AG, Corporate TechnologySlide 1 Project: IEEE P802.15

17th July 2008

Horak et al., Siemens AG, Corporate TechnologySlide 1

doc.: IEEE 802.15-08-0523-04-0vlc

Submission to IEEE 802.15 SG VLC

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)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 CommunicationsDate Submitted: 18th July 2008Source: 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, GermanyVoice: +49-89-636-45850, FAX: +49-89-636-51115, E-Mail: [email protected]

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.

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doc.: IEEE 802.15-08-0523-04-0vlc


Optical Radiation Requirements for Light-Emitting Diodes and Implications

for Visible-Light Communications (VLC)

Werner Horak and Ronald Neuhaus Siemens AG

Corporate Environmental Affairs & Technical Safety

Joachim W. WalewskiSiemens AG

Corporate TechnologyInformation & Communications

Munich, Germany

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doc.: IEEE 802.15-08-0523-04-0vlc


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

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Outline

• Historical background

• Incoherent light sources

• Eye-damage according to lamp standard

• Skin-damage according to lamp standard

• Summary and outlook

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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

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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, …)

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Eye-damage mechanisms for visible light

1. Thermal• Burning of retina• Relevant quantity at retina: Irradiance [W/m2]

2. Photochemical (‘blue hazard’)• Photo-induced damage of retina• Strong wavelength dependence (blue!)• Relevant quantity at retina: Radiant energy [J/m2]

3. Cataract• UVA (< 400 nm)• Clouding of eye lens• Exposure limit: 10 kJ/m2 over 28 800 s (350 mW/m2 on

average)

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Eye-damage mechanisms for visible light: cataract

400 500 600 7000

0.2

0.4

0.6

0.8

1

Wavelength [nm]

No

rma

lize

d L

ED

Sp

ect

ral

Po

we

r slow modulation

fastmodulation

Level of UVA emission intimately dependent on white-light generation scheme

Decision: UVAnot considered in

this talk

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Eye damage: Averaging field of view for ‘blue hazard’

Ang

le o

f ac

cept

ance

/rad

0.1 1 10 100 1 103

1 104

0

0.05

0.1

0.15

1.7 103

FOV t( )

9.999 1030.25 t

Exposure duration/s

• “Smearing out” of retina image due to random eye movement• Potentially lower luminenous intensity

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Eye damage: Risk groups according to IEC 62471

1. Exempt• No photo-biological risk• Critical exposure duration: 10 000 s for ‘blue’, 10 s for

thermal

2. Low risk• “Behavioural” protection (avoiding displeasing illuminance,

…)• Critical exposure duration: 100 s for ‘blue’, 10 s for thermal

3. Medium risk• Protection due to blinking etc.• Critical exposure duration: 0.25 s

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Typical white LEDs used in our laboratory

Nichia NSPW500CS:120 mW, 260 mrad, 18 cd, ~ 1 lm

Ostar E3A30 W, 2.1 rad, 150 cd,~ 400 lm

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Eye damage (past): LED exemption limits based on laser safety standard (IEC 60825-1)

IEC: exemption limits for LEDs (Class 1)

0,01

0,1

1

10

100

1000

10000

color (peak wavelength)

Lu

min

ou

s in

ten

sit

y [

cd

] 100 mrad

90 mrad

80 mrad

70 mrad

60 mrad

50 mrad

40 mrad

30 mrad

20 mrad

15 mrad

11 mrad

9 mrad

7 mrad

5 mrad

3 mrad

1,5 mrad

blue light thermal hazard

Nichia NSPW500CS:120 mW, 260 mrad, 18 cd,

~ 1lm

Ostar E3A30 W, 2.1 rad, 150 cd,

~ 400 lm

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Comparison: exempt eye damage limits for lasers and lamps

CIE/IEC comparison of the exemt limits

0,01

0,1

1

10

100

1000

10000

100000

0,01 0,1 1 10 100 1000 10000 100000

CIE luminous intensity [cd]

IEC

lum

ino

us

inte

nsi

ty [

cd]

w hite

blue1

blue2

verde

green1

green2

green3

yellow

orange

amber

red1

red2

x = y

• Red LEDs: Higher limits today

• Green LEDs: Mostly higher limits today

• Blue and white LEDs: higher/lower limits today

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Eye damage (today): Exempt group according to IEC 62471

CIE: exempt group

1

10

100

1000

10000

100000

LED color

ma

x.

Lu

min

ou

s in

ten

sity [

cd

]

100 mrad

80 mrad

60 mrad

40 mrad

20 mrad

11 mrad

1,7 mradmight be reached

„unreachably“ high

Ostar E3A30 W, 2.1 rad,

150 cd, ~ 400 lm‘borderline’ exempt!

Nichia NSPW500CS:120 mW, 120 mrad,

18 cd, ~ 1 lmexempt!

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Eye damage (today): Low-risk group according to IEC 62471

CIE: low risk group

1

10

100

1000

10000

100000

LED color

ma

x. L

um

ino

us

inte

nsi

ty [

cd]

100 mrad

80 mrad

60 mrad

40 mrad

20 mrad

10 mrad

2 mrad

Ostar E3B30 W, 2.1 rad,

150 cd, ~ 400 lmlow risk

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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

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Skin-damage mechanisms for visible light

1. Thermal• Burning of skin• 3 kW/m2 over 10 s• Corresponds to Ostar-E3A emission focused to ~ 3 cm2

• Potential issue!

2. 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!

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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

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Overall good news

• LED manufacturer will conduct classification for you!

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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)

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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

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(Our) Vision

Let’s create a safety-compliant VLC technology!

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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

Documents

Doc.: IEEE 802.15-08-0523-04-0vlc Submission to IEEE 802.15 SG VLC 17th July 2008 Horak et al., Siemens AG, Corporate TechnologySlide 1 Project: IEEE P802.15