Stroboscopic flicker, defining light that exacerbates migraines

Natalia Lesniak, Msc, LC, IESCooley Monato Studio

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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?

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

Flicker it does bother people

FlickerFlicker●Modulation in light output

over time

Stroboscopic effect●Luminous flux modulation,

perceived when objects are in motion

Photo: Lighting Research Center

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

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 CARELipton RB et al Headache. 2001.

Over 28 million people afflict in the USA (age 12 & up)21 million women7 million men

1 in 125 sufferer from migraines

$13 billion estimated annual costs (direct & indirect)• Emergency room visits• Hospitalization• Medication use• Clinical visits• Lost work days • Pain of migraine sufferers

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 CenterPhoto: Courtesy of the British Migraine Association

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

Flicker Metrics

Source: IES Lighting Handbook

Flicker Basics

Most lighting

systems operated

on AC mains

produce flicker

Source: DOE SSL TECHNOLOGY FACT SHEET: Flicker

Flicker Metrics

Good

Bad

Source: DOE SSL TECHNOLOGY FACT SHEET: Flicker

Flicker Metrics

Most lighting

systems operated

on AC mains

produce flicker

Flicker while dimming

Source: Philips Lighting

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)

driversPhoto: Lighting Research Center

(Excluding power issues)

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

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 % FlickerIf % 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%

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

Acceptable

Not Acceptable

Recommended Practices

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 Flickerhttp://www.lrc.rpi.edu/programs/solidstate/assist/pdf/AR-FlickerApps.pdf

Applications:Where flicker matters

• Industrial spaces (rotating machinery)

• Hospitals

• Offices/classrooms

• Video conferencing/filming studios/security camera

• 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

Human visual system & ipRGCs

Source: H. Kolb. 2003, http://www.ledc.co.uk/oct.htm

ipRGCs

Source: Dacey, 2005

Melanopsin expressing retinal ganglion cells (found in humans in 2001)

Vertebrate melanopsin

gene – Opn4m

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

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

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

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

Thank You!

This concludes The American Institute of ArchitectsContinuing Education Systems Course