Flashing LEDs & epileptic fits?


Senior Member
It's the summer silly season down here in NZ,& with meagre local news our reporters are seizing on global snippets to pad out papers. Well you can only print so many Comet McNaught pix I guess ..

One just to hand is the use of solar powered LEDs as &quot;cat's eyes&quot; road studs, apparently first used on Britains A413 in Bucks. early 2006 =&gt; <A href='http://www.astucia.co.uk/news_detail.aspx?news_id=22 ' Target=_Blank>External Web Link</a>, with press release <A href='http://www.intertraffic.com/marketplace/mypage/pressreleases_detail.asp?mypageid=206&amp;newsid=590 ' Target=_Blank>External Web Link</a>

On the face of it a brilliant road safety idea, but a similar installation on the Essex A20 has just been implicated in possible epileptic fits amongst road users<A href='http://news.bbc.co.uk/1/hi/england/essex/6226285.stm ' Target=_Blank>External Web Link</a> with installation halted until claims are investigated. Apparently these Astucia installations have 100Hz flashing, which (on the face of it) should be well above the acknowledged 7-10Hz epileptic danger rate. Even normal viewers are well known to become confused at refresh rates around these frequencies of course. Aha- so THAT's maybe why your electronics class has trouble remembering Ohm's Law !

Since Picaxes are such naturals for LED flashing, school users should be alert to this epileptic photo triggering mechanism, especially if any kids are prone to fits.

Temptingly this may be a PICAXE PROMOTIONAL OPPORTUNITY for some bright spark keen to investigate the phenomena. I can just see it now on BBC news - &quot; 16 year old XXX XXXXX of XXXXX school investigated the flashing LED cat's eye fit phenomena for a science project using just a &#163;1 &#169; Picaxe &#8482; microcontroller. Results are being scrutinised, but evidence already suggests ... &quot;

Anyone? Stan.

Edited by - manuka on 21/01/2007 21:33:44


Oh dear oh dear.
The strobe effect has long since been associated with provoking epileptic fits. I think thats pretty undeniable.

I have driven sections of road which use these LED cats eyes. I can't see the problem. They must be a very fast duty and their intensity is very low. (PS I've just seen your mention of 100Hz... really? )

Personally, the move towards LED rear lights on cars I find annoying as I can see them flashing - especially on 3 lane traffic jams at night where peripheral vision is more sensitive to flicker.

No-one has mentioned that (yet) for provoking fits. It'll come....

Ah yes, I remember the people trying to sue Vodafone for brain damage...

The cycnic in me says &quot;compensation&quot; and &quot;research grants&quot; and &quot;moaning for moanings sake&quot;. I'd better send a letter in to see if I can get some cash for the stress and trauma it has caused me!

Edited by - Dippy on 21/01/2007 22:40:17


Senior Member
Using these same ideas, I once put a picaxe to good use by making some flashing eye glasses to help people with sleeping disorders get to sleep.

It had a couple of different flashing frequencies, because apparently the reason a person has a sleep disorder affects the brain in different ways - so different frequencies have different effects (although hopefully not inducing an epileptic fit!).

It is still a cross-over between art and science, and so my psych friend who is in the process of making these things commercially helped me out with a bit of theory and the freqs involved.

The device used a pair of sunglasses (could be sleeping mask) which had a series of 4 LEDS around each eye which then flashed at particular frequencies. After 15 mins it turned off.

The friend who used it reported benefits some of the time - it really depended on her mental state on any given night. Overall it was worth the effort to make it. So thanks picaxe - for being part of a simple medical solution.

cheers, Arnie


New Member
If you want to be really cautious the rate for photosensitive epilepsy is 2Hz to 55Hz. 100Hz is still well outside this range. But why don't they make the frequency 1000Hz - at least then there will be no weird strobe effects.

Here in Australia there are clear rules about driving and epilepsy. Anyone who has a fit is not going to be able to drive for at least 5 years, and even after that they will find it very difficult to get their licence renewed, even when on medication.

So there should be no issue with people driving and having seizures, because those people ought not to be driving. There are many other things that will also trigger seizures in those people - eg lights flickering between trees planted along the side of the road, and flashing lights from emergency vehicles.

And yes, it could be an interesting research project, though I would be careful about taking it as far as finding a willing subject with epilepsy who is prepared to stare at a picaxe flashing a led. You might want some IV diazepam on hand!

Edited by - Dr_Acula on 21/01/2007 22:52:33


Senior Member
There's a bit of road not so far from here with this sort of thing, I found an odd effect when I first noticed them. When looking right at them no apparent flickering but when they caught the side vision they flickered... focus on the flicker and it's gone!

I'm sure there's an explaination &amp; some study done in the past.



Senior Member
I occasionally suffer migraines ( only the aura not the brain crushing headaches, but it can still be debilitating short-term ) and I'm extremely sensitive to lights flickering.

I usually notice fluorescent tubes on the way out well before anyone else does, and I can perceive them flickering even when others looking at them cannot. I've had to leave consumer electronics shops before now because a whole bank of TV's can be just too much. All that's at 50Hz in the UK. I actually found 100Hz TV's to be far worse than 50Hz.

As with colin and dippy, greatest sensitivity and detection is in peripheral vision and for me it's the flashing rather than frequency which can trigger a migraine. Even 1Hz and lower can do that, and sometimes just a single flash of bright light. High-contrast, black and white striped patterns are nasty. Analogue scopes can be particularly good triggers at the wrong scan rate. None of these are guaranteed triggers so there are other factors at play which can increase or decrease sensitivity.

I tried those glasses ArnieW comments on, lost my sense of balance and was very nearly sick !

Although NASA have estimated one in 10,000 have photosensitive epilepsy, I'm happy to accept that I am outside the norm, that people shouldn't be able to perceive such flickering, nor be affected by it at 'safe frequencies', but I can say for certain that I am. I wish I wasn't, but it wasn't my choice.

I've noticed on video games sold in the UK that the French language section has a warning about epilepsy but there is usually none in other languages, and there unfortunately seems to be pervading feeling in the UK and perhaps elsewhere that people who complain about such things are making it up because neither they nor any of their friends have ever suffered from such effects and some 'scientists' say it can't happen at all at those frequencies. If only all humans fitted the perfect model :)

I don't think PICAXE's need to come with a safety warning ( swallowing them is bad too ), but a warning about flashing LED's in the manual would be no bad thing. The blinding brightness of the blue LED's on the Rudolph kit when it flashed on triggered a migraine, so I can perhaps claim to be the first PICAXE victim ( I didn't sue Rev-Ed ).

Giving the cursory warning in class makes sense, but then the little buggers are likely to go straight for the target frequency to test the concept.


New Member
The peripheral vision of the eye is much more sensitive to movement than the central vision. The biological explanation is that the eye notices movement in the periphery, and then the eye moves so you can see what it is that is moving. It is quite possible to see 100Hz flicker in the peripheral vision and there is nothing unusual about that causing migraines.

Any flashing light at these frequencies will be even more obvious if one moves ones head, or is moving in a car, causing a most disconcerting strobe effect. This isn't a problem with incandescent lights at 50hz because they never change much in brightness, but anything like a LED is going to need a much higher frequency before it appears to be on constantly with no flicker.

I am reminded of an experiment a car manufacturer did (Holdens) in the mid 1980s with a totally digital dashboard. It was all multiplexed and looked fine until you moved your head quickly. It only lasted one model.



Senior Member
Human peripheral vision no doubt evolved as an early alert to sabre tooth tigers &amp; the like stalking us in the long grass, &amp; it certainly responds to flicker rates well beyond the normal 20-30Hz POV (persistence of vision) threshold. I wonder if the road stud LEDs shouldn't be &quot;dolloped&quot; white LED types, as the phosphor after glow serves to even out illumination flicker.

I've seen simpler problems qualify for MOST generous R&amp;D grants, so anyone capable in Europe after a research project should maybe put their hand up -pronto. I'm half tempted to do so from the other side of the world in fact! Stan


We have different coloured thingies depending on their application/position in road, so the white markers would already be 'dolloped'.

Also remember that they have reflectors so its not exactly on/off, more like on/dimmer.

Go for it Stan, though I can't imagine any Government handing out grants for epileptic projects if you don't have a medical/relevant background? (Come to UK as nothing would surprise me here!)


New Member
Shouldn't be too hard to get money out of the British Government - they gave 250,000 pounds to research a flying microwave oven <A href='http://en.wikipedia.org/wiki/EmDrive' Target=_Blank>External Web Link</a>. Stan, it sounds like they really do need some help if they have actually rolled out a device flashing at 100Hz in the middle of the road. They either need to run it much faster, or use phosphors to smooth things out. I can do the medical side and you can do the technical side??

Edited by - Dr_Acula on 23/01/2007 00:17:35


Senior Member
I'm in no position to really comment, and lack of demonstratability seems key, but I have to smile a little at the refutation of the EmDrive, that it can't and won't work because all the knowledge we have proves it won't, and all the scientists agree. How many times has that been said before our knowledge has been updated to take into account the fact that something does work ?

As to the investment, I don't think it's an excessive amount to prototype and assess it ( and a bargain had it been shown to work ), and considerably less than the millions we paid Pillinger &amp; Co to crash Beagle 2 into Mars; an entirely predictable end result in hindsight, and as some of us warned at the time, given that the project was run mainly on hype and a lot of the systems hadn't been properly tested or proven before launch.

Edited by - hippy on 23/01/2007 01:16:56


Senior Member
Mmm -maybe this &quot;push&quot; phenomena explains why domestic microwave ovens occasionally become unbalanced? But -splutter - &#163;250k!

Us colonials will normally check almost anything for just a dozen beer. For another dozen we'll even look to ensuring world peace, eliminating bird flu &amp; getting teenagers to listen to decent quiet music. Upon reflection,the latter may need a 3rd dozen ... Stan

Edited by - manuka on 23/01/2007 11:06:17


It reminds me of Cold Fusion.

Loads of odd subjects are released to the press. If it takes off, and enough people get excited, then a grant may be offered.

You know the sort of thing; research that now tells us that adding milk to tea may cancel out the beneficial goodness in tea.

Of course the researcher will be closely watched by lawyers and others who hope to make a few quid.

An old colleague of mine was trying to get compensation out of Phillips for the headaches that his DECT phone gave him. He'd been watching those researchers making great claims for microwave-related brain damage from cellular phones.

Bandwagonitis and compensation culture. Anyway, enough of my cynicism - back to PICAXE projects...


Don't just talk about it, ACT!
There are grants to be had, you just need to apply to the right people with a convincing project plan and convincing arguement that you have the required ability and see the project through. That requires TOTAL commitment which is why &#163;250k is about the going rate.
Have a look at the NESTA site.
You will find many projects not far removed from some of the ones described on this forum have obtained funding.
Don't be amazed at what others have got. Be amazed at what YOU managed to get.

As for Beagle 2. I was one of those &quot;as we predicted&quot; that Hippy describes. But how many of us actually formally voiced our concerns. Clearly not enough. Having a groan and moan with your mates has no effect on anything. You need to be heard by people who can make a difference and in a manner that will make them listen.

Edited by - beaniebots on 23/01/2007 18:40:35


Senior Member
&#163;250K won't go that far when doing research. It's such a footling amount of money that it's worth spending it just for the mere <i>possibility </i> of an &quot;anti-gravity&quot; drive, or similar science-fiction like device.

The US military finances all sort of peculiar research on the slim chance that it might produce something that gives their forces an advantage. When your budget is measured in billions, what's a few thousand?


Senior Member
For those eager to dip into this apparently tempting R&amp;D field, I should point out that my own tertiary level experiences indicate approx. only a 1 in 10 funding &quot;strike rate&quot; may result.

It's not just credibility,since you &amp; your team may typically put in a demanding week-10 days angling for each funding grant, only to be declined due to competing factors often outside your control. The parallels with fishing or playing lotteries are distrbingly close.

Then again a pot luck application may teasingly be randomly approved. I recall some 20 years back in 1987 receiving an untagged ~$$$$($) grant to cover &quot;2 way radio gear&quot; that I must have spent all of 5 minutes applying for. It turned out an earthquake had synchronised with the funding committee's meeting,serving to apparently heighten their awareness of the need for disaster communications... Stan


Senior Member
&quot;It turned out an earthquake had synchronised with the funding committee's meeting,serving to apparently heighten their awareness of the need for disaster communications...&quot;

Ah, yes - the unimaginable value of &quot;right time, right place&quot; ;-)



New Member
The strike rate for grants is about 1 in 8 in the medical world, and they never give you much feedback about why some work and some don't. But then again, over the last 4 years I have managed to get three health programs funded with a total value of $Au1.2 billion, so the payoff makes it worth persevering. The trick is to get politicians to fund things that both improve our lives and also improve their chances of being re-elected, but without being seen to be pork barrelling.
Unfortunately, the NESTA site says they only back UK startups.
The Astucia website says their leds flash &quot;between 1Hz and 100Hz&quot;. They also say they use micro controllers to manage the solar charging. I wonder if they use picaxes? If they do use picaxes or something similar, I presume they are hitting the led with a big current surge in pulses to get a higher apparent brightness. They would have to do this as they say the unit is solar powered and has to run a week with no charge, so a luxeon 1W or 5W led would be out of the question.
Then one has to calculate the on time and off time of the led to get an average of say, 30mA. I have pulsed leds with 1A and a 1:30 duty cycle with no problems, so say they have a 1:30 duty cycle and 100Hz the on time will be 1/30th of 10ms, or 0.3ms.
Maybe the microprocessor they are using is struggling to give pulses shorter than this? The picaxe, of course, can use pulsout to produce much shorter pulses than 0.3ms.
Maybe they need a picaxe solution? It needs to charge a battery with solar power, ideally use only one 1.2V cell so might need a stepup converter, a light sensor, and be able to flash a led with high current pulses. I feel this might need a trip to the laboratory...


Senior Member
Dr_Acula - I like your line of thought on this topic. How about we discuss this more 1:1 rather than clog the Forum ? That's of course unless other Picaxers actually find some enjoyment in our rustic colonial banter. Stan


New Member
We can do both. I have sent you an email. I'm also doing some back of envelope calculations with solar panel areas, average UK solar flux levels and step up converters. A question for those in the UK - has global warming meant the sun shines a bit more, or is it still that things can go a week in winter with no sun at all?


I 'm playing the cynic here, but take a look at those pics in the Astucia link. They appear to be on long time exposure or very slow shutter speed. You can see car tail lights but no cars. The LED's are still relatively dim. How bright are they real time? Is it worth it? Whats wrong with the old reflective type which use the energy from the car? Why waste Earth's precious resources to make thousands of solar panels when existing light can be reflected?

Its good to see how far you can take an idea, but sometimes technology is used because you can, not because you should.

Stan and Doc you could still show em how its done - use the research grant to prove that the old way works best. I bet the hi tech ones cost a bomb for the tax payer.


Its quite apparent that this thread has excited quite a few opinions. Stan has a good suggestion that he and Dr.Acula communicate 121 as there is not a lot of PICAXE content here.

I am a little cycnical too (like steirny) that electronics as being used for its own sake (like lasers) - but having seen them I can say that they are brighter than reflector-only. Having said that the Astucia devices have reflectors too.

&quot;...struggling to give pulses shorter than this?&quot; I don't think so! I can't see any full spec. but they could EASily flash faster - my guess would be that Astucia have done a little more than a morning's work on getting a compromise between power consumption and brightness perception and POV. This, after all, is NOT rocket science.

Cost, yes, this must be higher.
By how much? Not a clue. Litte PV + PIC etc, maybe a tenner? But I bet your bottom dollar that the installation cost is by far the largest percentage. (All those Hairy labourers @ &#163;20 an hour.) Service costs is another thing of course.... 10 years down the line will the Highways people pay 10s of thousands to change batteres etc..?

But remember, the sections where these have been put down are limited and no doubt carefully manipulated surveys are being carried out to see if they provide any benefit (cost vs lives saved/injuries/damage).

Personally, I find there are many more things on the road that annoy me. Low level fog lights on in clear weather, cars covered in blue LEDs, lorries lit up like Xmas trees, LED backlighting, cyclists 3 abreast, my ex-Mother-in-Law...

Enough. Back to PICAXE.


Senior Member
Agreed- getting OT, but here's a teaser from the research on a shoestring corner =&gt;<A href='http://www.playfuls.com/news_004152_Microwave_Oven_Can_Sterilize_Sponges_Study_Reveals.html ' Target=_Blank>External Web Link</a>

Maybe the collective Picaxe community should at least contact that UK firm,Astucia,as no doubt they're wailing &amp; gnashing their teeth due to their little darlings being put on ice, while their &#163;20/hr installers twiddle their thumbs. This was the slant of my initial posting of course. Stan

Edited by - manuka on 24/01/2007 09:36:33


Stan, you ARE a tease!
I thought that link was going to be a photo of a 600 foot long breadboard operated by 15 blokes with beards!

I've just remembered - 'BIMboard' thats the make of breadboards I use.

Microwaves was a large part of my MSc course but I've forgotten nearly everything... ah me!


Senior Member
Took a quick look at the photos on their site. The main components are reflectors not electronics. Great marketing! Ron Popeil would be proud.

How many research $$$$ can I get for burying a solar light in the pavement?

Edited by - Mycroft2152 on 24/01/2007 10:48:51