ASSESSMENT OF NON-COHERENT LIGHT SOURCES

Transcription

1 ASSESSMENT OF NON-COHERENT LIGHT SOURCES David Egan Snr Team Leader Laser Science Support Orion Laser Facility AWE, UK Page 1

2 Introduction Laser safety is accepted However there is a certain reticence to accept LEDs and lamps safety. Driven by the use of LEDs and lamps in everyday life. Not perceived as hazardous. However there are inherent hazards Page 2

3 LED lighting Page 3

4 LED lighting Strong economic incentive to overhaul existing street lighting and convert to LED lighting Early LED designs emitted excessive blue light, which contributes to disability glare/visual impairment Outdoor LED lamps (still being installed) have a Correlated Color Temperature (CCT) index of 4000 K o Daylight is ~ 6500 K o Typical sodium lamps has a CCT of 2100 K Newer LEDs are ~ 3000K, which is slightly warmer in tone and has less impact on humans and wildlife Page 4

5 LED lighting Circadian disruption: White LEDs estimated as > 5 times more effective in influencing circadian physiology vs. a HPS lamp Brighter residential night time lighting is associated with reduced sleeping times, lower sleep quality, impaired daytime functioning and obesity High CCT LEDs could impact the long-term health of exposed populations Page 5

6 Blue light hazard Blue light is hazardous to the retina, especially due to reduced pupillary constriction compared to white light (- intrinsically photosensitive retinal ganglion cells) - Circadian Rhythm Disruption Fatigue Peak of hazard 440 nm High luminance or hot spots due to small source size Glare from increased scatter (due to shorter wavelengths) Afterimages Effects on long-term health Uncertainty regarding chronic effects of low doses on eye damage, e.g. Age-related macular degeneration (AMD) Page 6

7 Work environment Page 7

8 COHERENT AND NON-COHERENT SOURCES Laser Differences LED/Lamp Low divergence Highly divergent 1/r 2 Single wavelength (λ) Uniform distribution Point source Broad band (Δλ) Spatial variation Extended source Similarities Photobiological effects are the same Page 8

9 UNIT Radiometric Photometric Parameter Unit Symbol Parameter Unit Symbol Radiant power W P Luminous flux lm Φ Radiant intensity W.sr -1 I Luminous intensity (candela) lm.sr -1 (cd) I Irradiance W.m -2 E Illuminance (lux) Lm/m 2 E Φ Radiance W.m -2.sr -1 L Luminance lm.m -2.sr -1 (cd.m -2 ) L Φ Radiometric properties: radiant energy or power regardless of whether or not the light is invisible or visible. Photometric properties: visible properties of the light source whether or not the light stimulates a visual response. Page 9

10 IEC Hazard bands IEC Hazard Band Wavelength range Exposure Limit Type Actinic UV Skin and Eye 200nm to 400nm Irradiance Eye UV-A 315nm to 400nm Irradiance Blue Light small Source 300nm to 700nm Irradiance Blue light extended Source 300nm to 700nm Radiance Retinal Thermal 380nm to 1400nm Radiance Retinal Thermal (weak stimulus) 780nm to 1400nm Radiance Infrared Hazard to Eye 780nm to 3000nm Irradiance Skin Thermal Hazard 380nm to 3000nm Irradiance Page 10

11 Irradiance Irradiance (radiant power per unit area) Radiant Exposure (radiant energy per unit area) Light source, LED, lamp Radiant emission of light source Measured irradiance here Page 11

12 Summary Exposure Limit Tables (skin and cornea) - IRRADIANCE Hazard name Relevant equation Wavelength range (nm) Exposure duration (sec) Limiting aperture mrads (deg) EL in terms of constant irradiance Wm -2 Actinic UV skin and eye E S = E λ S(λ) Δλ < (80 ) 30/t Eye UV -A E UVA = E λ Δλ > (80 ) 10000/t 10 Blue light small source E B = E λ B(λ) Δλ >100 <11 100/t 1.0 Eye IR E IR = E λ Δλ > (80 ) 18000/t Skin Thermal E H = E λ Δλ <10 2π sr 20000/t 0.75 Page 12

13 SPECTRAL EFFICACY Spectral Weighting function S uv (λ) UV hazard function Suv (λ) Spectral efficacy for causing photokeratitis/erythema WAVELENGTH (nm) Page 13

14 SPECTRAL EFFICACY Spectral Weighting function B BLS (λ) 1 Spectral wieghing function: Retinal blue light B(λ) Spectral efficacy for causing retinal photochemical damage WAVELENGTH (NM) Page 14

15 Irradiance (Wm-2) Irradiance limits - skin and eye 10,000, ,000, , Wieghted irradiance exposure limits vs time constant exposure 10, , Time (sec) Actinic UV Eye UVA Blue light small Eye IR Skin thermal Page 15

16 Radiance (W.m-2.sr-1) - watts per square metre per steradian Light source, LED, lamp Radiance requires solid angle to be clearly defined in the optical system αmin: rads αmax: rads Radiance cares about the (angular) size of the source Page 16

17 Summary Exposure Limit Tables (retina) - RADIANCE Hazard name Relevant equation Wavelength range (nm) Blue light L B = L λ B(λ) Δλ Exposure duration (sec) Limiting aperture mrads (deg) 11* (t/10) 11 11* t 100 EL in terms of constant irradiance Wm /t 10 6 /t 10 6 /t 10 Retinal thermal L R = L λ R(λ) Δλ < * (t/10) 50000/(α*t 0.25 ) 50000/(α*t 0.25 ) Retinal thermal (weak visual stimulus) L B = L λ B(λ) Δλ >100 < /α Page 17

18 SPECTRAL EFFICACY Spectral Weighting function R(λ) Spectral wieghing function: Retinal thermal R(λ) 10 Spectral efficacy for causing retinal thermal damage WAVELENGTH (nm) AWE Orion Laser Facility, AWE, Page 18

19 RADIANCE (W.m -2.sr -1 ) Radiance limits - retina Weighted radiance exposure limits vs time for constant exposure Blue light retinal thermal min retinal thermal max retinal thermal weak max retinal thermal weak min 1E TIME (sec) Page 19

20 Risk band classification 4 Risk Groups (RGs) based on potential acute hazard: RG 0 (or Exempt) no photobiological hazard under foreseeable conditions RG 1 (low risk) no risk under normal conditions of use, limited by normal behavioral limitations on exposure RG 2 (moderate risk) no risk due to aversion response to bright light sources (up to 0.25 s) RG 3 (high risk) potential risk even from momentary exposure Page 20

21 BS EN 62471:2008 Exposure limits summary table Hazard Wavelength range (nm) Risk Group Time limit (s) Emission limit RG W.m -2 Time dependent exposure limit Actinic UV skin and eye 200 to 400 RG W.m -2 RG W.m -2 ELV = 30/t W.m -2 ELV = 30 J.m -2 RG-3 if RG-2 is exceeded RG W.m -2 ELV = 10 W.m -2 (t 1000s) Eye UV-A 315 to 400 RG W.m -2 ELV = 10,000 J.m -2 RG W.m -2 (t < 1000s) RG-3 if RG-2 is exceeded Page 21

22 BS EN 62471:2008 Exposure limits summary table 2 Hazard Blue light Small source C Wavelength range (nm) 300 to 700 Risk Group Time limit (s) Emission limit Time dependent exposure limit RG W.m -2 ELV=1 W.m -2 (t > 100s) RG W.m -2 ELV = 100 J.m -2 RG W.m -2 RG-3 if RG-2 is exceeded (t 100s) Blue light Extended source R 300 to 700 RG ELV=100 W.m -2 sr -1 ELV = 100 W.m -2 sr -1 (t >10000s) RG ELV=10000 W.m -2 sr -1 ELV = 10 6 J.m -2 sr -1 RG ELV= W.m -2 sr -1 RG-3 if RG-2 is exceeded (t 10000s) Page 22

23 BS EN 62471:2008 Exposure limits summary table 3 Hazard Wavelength range (nm) Risk Group Time limit (s) Emission limit Time dependent exposure limit Retinal thermal source 380 to 1400 RG-1 10 ELV=28000/α W.m -2 sr -1 ELV=50000/α.t 0.25 W.m -2 sr -1 RG-0 10 ELV=28000/α W.m -2 sr -1 RG ELV=71000/α W.m -2 sr -1 (10μs t, 100s) RG-3 if RG-2 is exceeded Retinal thermal (Weal visual stimulus) 780 to 1400 RG ELV=6000/α W.m -2 sr -1 RG ELV=6000/α W.m -2 sr -1 ELV =6000/α W.m -2 sr -1 RG ELV=6000/α W.m -2 sr -1 RG-3 if RG-2 is exceeded (t > 10s) Page 23

24 BS EN 62471:2008 Exposure limits summary table 4 Hazard Infrared Hazard Front of eye Wavelength range (nm) 780 to 3000 Risk Group Time limit (s) Emission limit Time dependent exposure limit RG W.m -2 ELV=100 W.m -2 (t>1000s) RG W.m -2 ELV = t W.m RG W.m -2-2 (t 1000s) RG-3 if RG-2 is exceeded Skin thermal 380 to 3000 NA W.m -2 ELV = t 0.25 J.m -2 (t 10s) Page 24

25 Controls Unlike IEC there are no environmental controls stipulated. no labelling (covered under IEC ) no safety appointment no training requirements Risk based assessment E R I C P D Page 25

26 Summary Incoherent light sources are making more of an impact within scientific environments There are differences between coherent and incoherent light sources but photobiological effects the same. Requirement to assess the light source for the hazard it represents. Who is unaware that this is a problem? Page 26

27 Thank you for listening Any questions? Page 27