# "Some flashing lights sequences may affect photosensitive viewers"-- how do they know? **URL:** \ **Category:** Factual Questions\ **Created:** [July 2, 2021, 6:41pm UTC](https://boards.straightdope.com/t/some-flashing-lights-sequences-may-affect-photosensitive-viewers-how-do-they-know/945526 "2021-07-02T18:41:33Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![ekedolphin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ekedolphin/32/10003_2.png) [@ekedolphin](https://boards.straightdope.com/u/ekedolphin)\ **Post date:** [July 2, 2021, 6:41pm UTC](https://boards.straightdope.com/t/some-flashing-lights-sequences-may-affect-photosensitive-viewers-how-do-they-know/945526/1 "2021-07-02T18:41:34Z")
Watching “Loki” on Disney+, it provides a content warning: “Some flashing lights sequences may affect photosensitive viewers.” I remember when _Incredibles 2_ was released in theaters, it caused someone to suffer an epileptic seizure, and there were soon warnings all over the theater about it. But how do they determine that people with photosensitive epilepsy might have an adverse reaction to the flashing lights sequences, before the content is even released? Surely they don’t have someone in the room with epilepsy the whole time, and check a mark if he suffers a seizure! ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [July 2, 2021, 7:28pm UTC](https://boards.straightdope.com/t/some-flashing-lights-sequences-may-affect-photosensitive-viewers-how-do-they-know/945526/2 "2021-07-02T19:28:30Z")
> [@ekedolphin](#): > > But how do they determine that people with photosensitive epilepsy might have an adverse reaction to the flashing lights sequences, before the content is even released? Surely they don’t have someone in the room with epilepsy the whole time, and check a mark if he suffers a seizure! Flashing lights are known to trigger seizures in some people with epilepsy. So if you’re going to show a movie that features scenes with flashing lights, it’s a courtesy to give a heads-up to epileptics that they _might_ not want to watch it. It’s not necessary to wait until a viewer actually has a seizure before putting that warning up there. > **[Epilepsy | Seizures](https://en.wikipedia.org/wiki/Epilepsy#Seizures_2)** > > There is evidence that epileptic seizures are usually not a random event. Seizures are often brought on by factors (also known as triggers) such as stress, excessive alcohol use, flickering light, or a lack of sleep, among others. The term seizure threshold is used to indicate the amount of stimulus necessary to bring about a seizure; this threshold is lowered in epilepsy. > In epileptic seizures a group of neurons begin firing in an abnormal, excessive, and synchronized manner. This results in a ... ---
**Author:** ![Mean\_Mr.Mustard](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mean_mr.mustard/32/3865_2.png) [@Mean\_Mr.Mustard](https://boards.straightdope.com/u/Mean_Mr.Mustard)\ **Post date:** [July 2, 2021, 7:51pm UTC](https://boards.straightdope.com/t/some-flashing-lights-sequences-may-affect-photosensitive-viewers-how-do-they-know/945526/3 "2021-07-02T19:51:03Z")
As Machine\_Elf stated, flashing lights can trigger a seizure in one who is susceptible to having them. There are other triggers, including auditory ones, that can have a similar effect. In fact, strobes are sometimes used clinically in order to induce a seizure. Playing video games is another method of purposely causing a seizure. It can be weird. There was a famous case years ago where someone had a seizure upon hearing a specific television personality’s voice ([Mary Hart](https://www.upi.com/Archives/1991/07/11/Mary-Harts-voice-triggers-seizures/6469679204800/), one-time host of Entertainment Tonight). I personally knew of someone whose seizure trigger was hearing Phil Collins’ singing voice. mmm ---
**Author:** ![ekedolphin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ekedolphin/32/10003_2.png) [@ekedolphin](https://boards.straightdope.com/u/ekedolphin)\ **Post date:** [July 2, 2021, 7:59pm UTC](https://boards.straightdope.com/t/some-flashing-lights-sequences-may-affect-photosensitive-viewers-how-do-they-know/945526/4 "2021-07-02T19:59:13Z")
If all this is true, why didn’t they have warnings for _Incredibles 2_ until someone actually experienced multiple seizures while watching the film? I’m not epileptic and even _I_ could tell that that particular sequence could probably be hard to tolerate. ---
**Author:** ![gdave](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gdave/32/3683_2.png) [@gdave](https://boards.straightdope.com/u/gdave)\ **Post date:** [July 2, 2021, 8:17pm UTC](https://boards.straightdope.com/t/some-flashing-lights-sequences-may-affect-photosensitive-viewers-how-do-they-know/945526/5 "2021-07-02T20:17:53Z")
Because there’s no law that says any movie or TV show has to have these warnings. It’s become increasingly common, and I’m sure at this point for some studios it’s Standard Operating Procedure, but not every single production is going to have someone attached to whom it occurs to include this sort of warning. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [July 6, 2021, 10:20am UTC](https://boards.straightdope.com/t/some-flashing-lights-sequences-may-affect-photosensitive-viewers-how-do-they-know/945526/6 "2021-07-06T10:20:26Z")
> [@ekedolphin](#): > > If all this is true, why didn’t they have warnings for _Incredibles 2_ until someone actually experienced multiple seizures while watching the film? I’m not epileptic and even _I_ could tell that that particular sequence could probably be hard to tolerate. That movie was released in 2018. I’m not aware that anyone actually suffered a seizure while watching it, but **[an epilespy advocacy group expressed concerns about it](https://en.wikipedia.org/wiki/Incredibles_2#Health_hazards/epilepsy_problems)**: > Many disability advocates, including the [Epilepsy Foundation](https://en.wikipedia.org/wiki/Epilepsy_Foundation), have raised concerns that movie scenes with flashing lights, including that in _Incredibles 2_ of Elastigirl’s fight with the Screenslaver, can trigger seizures in viewers affected by [photosensitive epilepsy](https://en.wikipedia.org/wiki/Photosensitive_epilepsy).[[89]](https://en.wikipedia.org/wiki/Incredibles_2#cite_note-89)[[90]](https://en.wikipedia.org/wiki/Incredibles_2#cite_note-90)[[91]](https://en.wikipedia.org/wiki/Incredibles_2#cite_note-91) As a result, several theaters posted warnings for audiences.[[92]](https://en.wikipedia.org/wiki/Incredibles_2#cite_note-92) Disney told _[USA Today](https://en.wikipedia.org/wiki/USA_Today)_ that it appreciated those efforts, and then, in a memo, asked all theaters exhibiting the movie to warn audiences: " _Incredibles 2_ contains a sequence of flashing lights, which may affect customers who are susceptible to photosensitive epilepsy or other photosensitivities."[[93]](https://en.wikipedia.org/wiki/Incredibles_2#cite_note-93) > > In response to this, a re-edited version was released in the United Kingdom with all affected sequences altered so that any flashing lights and strobe effects now pass the [Harding test](https://en.wikipedia.org/wiki/Harding_test).[[94]](https://en.wikipedia.org/wiki/Incredibles_2#cite_note-94)[[95]](https://en.wikipedia.org/wiki/Incredibles_2#cite_note-95) In other words, there was a change of policy between 2018 and now, which is why “Loki” includes the warning you described. That web page includes a link to the Harding test, which apparently is useful in determining whether a given video clip has the potential to induce epileptic seizures: > **[Harding test](https://en.wikipedia.org/wiki/Harding_test)** > > The term Harding test is generically understood to mean an automatic test for photosensitive epilepsy (PSE) provocative image sequences in television content. This is properly known as a PSE test since the publication of the Digital Production Partnership (DPP) technical requirements and the DPP PSE Devices document (in the UK) updated in November 2018. > The Harding Flash and Pattern Analyser (FPA) is proprietary software that is used to analyse video content for flashing and stationary patterns... I think that provides a pretty definitive answer to your OP. ---
**Author:** ![dropzone](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dropzone/32/7515_2.png) [@dropzone](https://boards.straightdope.com/u/dropzone)\ **Post date:** [July 6, 2021, 11:09am UTC](https://boards.straightdope.com/t/some-flashing-lights-sequences-may-affect-photosensitive-viewers-how-do-they-know/945526/7 "2021-07-06T11:09:24Z")
[anecdote] My daughter went through a test for it during a multiple-day evaluation but came out okay. [/a]