Stroboscopic Flicker

Solid state lighting has made great advancements in the lighting field, but we still need to be attentive lighting quality and not get swept in by economic factors like cost & efficacy. Stroboscopic flicker has creeped back after it was eliminated from fluorescent lighting. Stroboscopic flicker what is it? How can we recognize it as designers and how do we decide where it is and is not acceptable (in architectural & automotive settings). We’ll present a few sample strobing rates for demonstration purposes.
Presented by: Natalia Lesniak

1. Stroboscopic flicker, defining light that exacerbates migraines Natalia Lesniak, Msc , LC, IES Cooley Monato Studio

2. Credit(s) earned on completion of this course will be reported to AIA CES for AIA members. Certificates of Completion for both AIA members and non-AIA members are available upon request. This course is registered with AIA CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. ___________________________________________ Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

3. Summary Solid state lighting has made great advancements in the lighting field, but we still need to be attentive lighting quality and flicker. Stroboscopic flicker has creeped back. How can we recognize it as designers and how do we decide where it is and is not acceptable. How does it impact our health and contribute to migraines?

4. Learning Points What is flicker & stroboscopic flicker Potential hazards from flicker What are the metrics used to determine flicker How to determine if a fixture has the potential of being hazardous How light potentially contributes to/aggravates photophobia & migraines

5. Flicker it does bother people

6. Flicker Flicker Modulation in light output over time Stroboscopic effect Luminous flux modulation, perceived when objects are in motion Photo: Lighting Research Center

7. Visible Flicker Distraction Neurological Problems ( Pokemon issus ) Epileptic seizure 1 in 4,000 have photosensitive epilepsy (~3-~70Hz) Increased autistic behavior Invisible Flicker (Stroboscopic flicker) Eyestrain, headache Migraine Stroboscopic effect (impacted motion perception) Reduced performance (reading or other visual tasks) Disruption of security systems & security cameras Photo: Lighting Research Center Potential hazards

8. Migraine Burden on Society Photo: Courtesy of the British Migraine Association Source: Lawrence D. Goldberg, The Cost of Migraine and Its Treatment. THE AMERICAN JOURNAL OF MANAGED CARE Lipton RB et al Headache . 2001. Over 28 million people afflict in the USA (age 12 & up) 21 million women 7 million men 1 in 125 sufferer from migraines $13 billion e stimated annual costs ( direct & indirect) Emergency room visits Hospitalization Medication use Clinical visits Lost work days Pain of migraine sufferers

9. What makes it worse Exposure duration Area of retina getting stimulation Brightness of flash (higher contrast in luminances Contrast of flash with surrounding luminance (think brightness contrast) so...higher contrast, intensity and longer exposure makes it worse Photo: Lighting Research Center Photo: Courtesy of the British Migraine Association

10. Photo: Gjon Mili , 1947, Stroboscopic image of ballerina Nora Kaye performing

11. Flicker Metrics Source: IES Lighting Handbook

12. Flicker Basics Most lighting systems operated on AC mains produce flicker Source: DOE SSL TECHNOLOGY FACT SHEET: Flicker

13. Flicker Metrics Good Bad

14. Source: DOE SSL TECHNOLOGY FACT SHEET: Flicker Flicker Metrics Most lighting systems operated on AC mains produce flicker

15. Flicker while dimming Source: Philips Lighting

16. What could cause flicker in LED lamps & fixtures Driver Dimmer AC LEDs DC LEDs with poor drivers LED lamps on electronic transformers Phase cut dimmers ( triac ) Pulse width modulation ( PWM ) drivers Photo: Lighting Research Center (Excluding power issues)

17. Will this LED source flicker? Request waveform or flicker information (missing from most cut sheets) Review samples Move your hand or a pencil Flicker wheel Look at the source w/ a digital camera Its more noticeable with higher contrast (black object on white back ground) Photo: Lighting Research Center

18. Recommended Practices Test for product for: Flicker frequency in hz (must be greater than 100 hz ) Determine % Flicker Multiply the frequency by 0.08 and round up to the nearest whole number to get the max Allowable % Flicker If % Flicker is LOWER than the Allowable Flicker, then the product is acceptable for all but the most unusually sensitive individuals. If frequency is difficult to determine, % Flicker shall not exceed 10%. 120 Hz x 0.08=9.6, thus MAX Allowed % Flicker is 10%

19. What to look for: Flicker Freq ≥ 100 Hz % Flicker ≤ Flicker Freq x 0.08 (normal populations), or % Flicker ≤ Flicker Freq x 0.0333 (special populations) Recap: 120 Hz x 0.08=9.6, thus MAX Allowed % Flicker is 10% % Flicker shall NOT exceed 10%. Recommended Practices

20. Acceptable Not Acceptable Recommended Practices

21. Recommended Practices 1789-2015 IEEE Recommended Practices for Modulating Current in High-Brightness LEDs for Mitigating Health Risks to Viewers (available since June 2015) IES Lighting Handbook ASSIST: Application Considerations Related to Stroboscopic Effects from Light Source Flicker http://www.lrc.rpi.edu/programs/solidstate/assist/pdf/AR-FlickerApps.pdf

22. Applications: Where flicker matters Industrial spaces (rotating machinery) Hospitals Offices/classrooms Video conferencing/filming studios/security camera

23. Places with limited/no motion (object/art lighting, accent or peripheral lighting where there the main light sources are free of stroboscopic flicker ) Use good judgement Applications: Where flicker matters less

24. Human visual system & ipRGCs Source: H. Kolb. 2003, http://www.ledc.co.uk/oct.htm Photo: http://www.advancedimagingpro.com

25. ipRGCs Source: Dacey, 2005 Photo: http://www.advancedimagingpro.com Melanopsin expressing retinal ganglion cells (found in humans in 2001) Vertebrate melanopsin gene –   Opn4m

26. Light & Migraines Light-induced discomfort and pain in migraine ( Vanagaite 1997) 88% of patients experience photophobia during migraines Over 50% of migraine sufferers find that a light stimulus have induced migraine attacks

27. Source: Nosada, 2010; Z. Molnar 2010 ipRGCs innervate nociceptive neurons in posterior thalmus (Po) Spinal trigeminal neurons innervate Po nociceptive neurons Po projects to visual cortex Meninges ipRGCs , the Brain, & Pain

28. Migraine symptoms Visual phenomena (various shapes, bright spots or flashes of light) Vision loss Pins and needles sensations in an arm or leg Speech or language problems (aphasia) Pain on one side or both sides of your head Pain that has a pulsating, throbbing quality Sensitivity to light, sounds and sometimes smells Lightheadedness, sometimes followed by fainting Nausea and vomiting Blurred vision Source: Mayo Clinic

29. Model of how light may contribute to the neural mechanism in exacerbating migraines ( Noseda 2010) LIGHT Source: A neural mechanism for exacerbation of headache by light Nature Neuroscience   13 ,  239–245  (2010) http://www.nature.com/neuro/journal/v13/n2/fig_tab/nn0210-150_F1.html Electrode recordings Possible path ways

30. Thank You!

31. This concludes The American Institute of Architects Continuing Education Systems Course