bright flashing bike lights and seizures

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Sep 2016
12:44pm, 24 Sep 2016
6960 posts
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I commute by bike most days, often clocking up 100+ miles per week through London traffic.

according to RoSPA, in 2014, 113 people were killed on bikes and 3,401 seriously injured, so i make no apologies for doing whatever i can to be seen (and before you ask, no i don't jump red lights or take unnecessary risks!). and as the winter draws in that will include the use of those extremely bright LED lights, often on "annoying flashing" mode.

the other day someone asked whether those flashing lights have an affect on people who suffer from epilepsy. Now, i know not all epileptics necessarily go in to seizure because of flashing lights but certainly it is an issue.

i've had a quick google and found nothing more than an organisation in Brighton asking cyclists not to use them as they "could" induce a seizure - the word 'could' being used to mean 'perhaps/possibly', I think.

so does anyone have any evidence of flashing bike lights causing seizures? i certainly wouldn't want that to happen to anyone but my guess is the chances of that happening are massively outweighed by the chances of a cyclist being not seen by a vehicle driver.

Sep 2016
1:12pm, 24 Sep 2016
7711 posts
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I would think the flash rate is too slow on most bike lights
Sep 2016
1:23pm, 24 Sep 2016
12211 posts
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Interesting thought. A quick research suggests that :

3% of people with epilepsy have photosensitive epilepsy (source: Epilepsy Foundation).

The flash frequency which may trigger the seizure varies widely (though faster flashes have a higher risk overall).

Risk of seizure is much affected by intensity, proximity of source, and, particularly, amount of visual field occupied. So eg intense flashing lights from a stage; or flashing from a tv whilst sitting close to the screen in a darkened room are high risk.

It is unsure whether flashing vehicle lights eg on emergency vehicles, trigger photosensitive epilepsy.

Many (most?) seizures can be prevented in pre-onset (the person usually has warning of a seizure) by avoidance, which can be just covering up one eye.

I would conclude that the risk of your lights triggering such a seizure are extremely small and therefore likely to be much less than your risk from traffic in situations of having inadequate lighting.

Link to Epilepsy Society

Two things: people may be adversely affected by light sensitivity without seizure: many more than are at risk of seizure. Do your lights affect them? In a busy urban environment, probably very little. And how many cyclist deaths and injuries are attributable to not being seen due to inadequate lighting? I suspect the answer is a fairly small proportion.
Sep 2016
1:30pm, 24 Sep 2016
12212 posts
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(Correction: Link is to Epilepsy Foundation)

Badger: I would say that at least one light I have flashes theoretically fast enough. However, it is a "broken pattern" which seems to be less risk. And whilst we are probably thinking of the bright white lights, red wavelengths can be riskier ie a rear light.
Sep 2016
7:46pm, 24 Sep 2016
597 posts
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Interesting question to which Dvorak has given a well considered answer.

I am photosensitive but not epileptic and I have had to walk out of several shops because their lighting displays make me ill. Perhaps I can use this photosensitivity to raise a connected point?

I am a regular cyclist and consider those bright flashing lights to be more than a nuisance. If I'm following one for a while, my eyesight becomes blotchy (like if you look at a bright light and even though you look away you still have the image obscuring your vision). If a cyclist with a bright flashing light comes towards me, I am alternately being so dazzled that I can't see where I'm going and then being plunged into darkness (my own steady light doesn't fully counter this). In both scenarios, my ability to proceed safely is greatly compromised.

Note that I am referring to only the very bright flashing lights. Flashing lights are a very good adjunct to constant lights since they state "this is a cyclist here", but they don't need to be so bright that they can be seen 1 mile away. I would suggest there is a possibility that using such bright lights could actually increase one's risk of being hit because the motor vehicle's driver's vision was impaired by the light.

Links to lighting regulations and cycle light brightness problems can be found at cyclinguk one of which states that lights should flash at a frequency of 1 - 4 Hz which is below the epileptic trigger point in Dvorak's and Badger's links, although Badger's link does say that epileptic episodes can be triggered by a rate of 3Hz. I've been unable to find any limits on maximum brightness, just minima.
Sep 2016
7:55pm, 24 Sep 2016
10525 posts
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A bit off on a tangent, but thise supoerbright lights can be blinding to people coming the other way. My commute is in part on a cycle path and the biggest danger is temporary blinding where you cant see and have to guess where to go to avoid the oncoming bright lights or veeruing into the verge at the side.
Sep 2016
12:11am, 25 Sep 2016
7714 posts
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I really hate people who have ultra-bright flashing front lights. If you can get by with a flashing front light, you're not using it to see where you're going so it doesn't need to be all that bright. Tilt the thing down so it isn't straight into other cyclists' eyes.

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About This Thread

Maintained by GordonG
I commute by bike most days, often clocking up 100+ miles per week through London traffic.


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