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 Post subject: Flashing lights warning
PostPosted: Sun May 14, 2006 10:03 
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While looking up photo epilepsy I came across this:

http://www.epilepsy.org.uk/info/photo_other.html

Bicycle lights (red light emitting diodes)

There have been cases where red flashing lights (used on the rear of bicycles) have triggered seizures in people with photosensitive epilepsy. This happened when the people were close to the lights as they were setting them up.


I thought it needed a mention. Some people can become epileptic after one photo-induced episode, so it's one to be careful with...

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PostPosted: Sun May 14, 2006 12:45 
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When I was little I was always told not to sit too close to the TV. I see this on a regular basis when I visit friends with children.
Are we losing a degree of knowledge nowadays? I know TV's no longer flicker like they once did, but a quick trip to a larger CURRY's store, and look at the "TV Wall" shows it is still present! 8-)

My own rear light has a setting for a simple pulse, AND a more complicated sequence - perhaps they should ALL feature this as standard :?: :idea:

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PostPosted: Sun May 14, 2006 12:47 
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What's wrong with an "on" setting? <serious question> Is it battery life, in which case, why not supplement rechargeables with a simple dynamo?


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PostPosted: Sun May 14, 2006 13:20 
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Roger wrote:
What's wrong with an "on" setting? <serious question> Is it battery life, in which case, why not supplement rechargeables with a simple dynamo?


You can get the battery life benefit with little drop in subjective brightness with a 1% to 5% duty cycle at say 1KHz. So I guess it's for visibility / noticability.

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PostPosted: Sun May 14, 2006 13:28 
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SafeSpeed wrote:
Roger wrote:
What's wrong with an "on" setting? <serious question> Is it battery life, in which case, why not supplement rechargeables with a simple dynamo?


You can get the battery life benefit with little drop in subjective brightness with a 1% to 5% duty cycle at say 1KHz. So I guess it's for visibility / noticability.


If that were so wouldn't/shouldn't car/van/tractor tail lamps also flash pitlane style when travelling at less than, say, 20 mph?


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PostPosted: Sun May 14, 2006 13:57 
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Roger wrote:
If that were so wouldn't/shouldn't car/van/tractor tail lamps also flash pitlane style when travelling at less than, say, 20 mph?


I think the cyclists are taking an advantage in the visibility arms race, and that to do so is reasonable because: 1) cycles are less common, 2) cyclists are potentially more vulnerable, and 3) cycles are usually travelling more slowly than other moving vehicles.

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PostPosted: Sun May 14, 2006 17:26 
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I remember reading an article on this - I couldn't find the original (excellent) piece, but this one should answer some questions...
Quote:
An LED's brightness is directly proportional to the current through it, which creates a challenge for low-voltage and battery-powered applications. But it's possible to increase an LED's brightness without increasing the system's power requirements.

The solution described here uses a high peak current to obtain a bright LED, and a low average current to minimize the power consumption. The LED oscillator circuit achieves these requirements by providing a low-duty cycle waveform with a short-duration "ON" time, and a long "OFF" time.

Pulsed LEDs can be brighter than direct-drive LEDs for two reasons. First, the human eye functions as both a peak detector and an integrator. Therefore, the eye perceives a pulsed LED's brightness somewhere between the peak and the average brightness.

http://www.elecdesign.com/Articles/Index.cfm?AD=1&ArticleID=2371

So there you have another reason to pulse the light rather than simply "always on".
They ARE more distinct when cycled than the always on setting.

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PostPosted: Sun May 14, 2006 17:54 
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Ernest Marsh wrote:
So there you have another reason to pulse the light rather than simply "always on".


Actually that's what I said...

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PostPosted: Sun May 14, 2006 19:48 
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SafeSpeed wrote:
Ernest Marsh wrote:
So there you have another reason to pulse the light rather than simply "always on".


Actually that's what I said...

Sorry, I wasnt sure whether you meant they APPEARED brighter, or WERE brighter! :lol: :idea:
I've tried to see if mine was brighter, but without equipment to measure, it's hard to tell whether what you are seeing is a genuine effect or a visual constancy! :shock: sorry that should be 8-) for safety's sake! :wink:

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PostPosted: Sun May 14, 2006 21:15 
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The instructions for flashing lights clearly indicate that you shouldn't look into them. I guess this is related to the epilepsy?

There is only one down-side to flashing lights that I know of: that they make judgement of distance harder. For this reasn I use one of these

Two lines of LEDs. I set one to constant and the other to flashing. £30 ish, but worth it.


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PostPosted: Sun May 14, 2006 21:42 
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Nice.

I presume it's not beyond the wit of man to do this sort of light cheaper, ie, instead of pulsing at, say, 500% rated power for 1/10th time / off for 9/10ths time, you could do 500% rated power for 1/20th time, 50% rated power for rest?


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PostPosted: Sun May 14, 2006 23:10 
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In case it's not clear from the photo, three of the LEDs on each line face backwards, and there is one on each side too. So 5 per line and ten overall.

It gives me a lot more comfort knowing I can be seen better from the sides using one of these.


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PostPosted: Mon May 15, 2006 04:17 
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Ernest Marsh wrote:
When I was little I was always told not to sit too close to the TV. I see this on a regular basis when I visit friends with children.
Are we losing a degree of knowledge nowadays? I know TV's no longer flicker like they once did, but a quick trip to a larger CURRY's store, and look at the "TV Wall" shows it is still present! 8-)

My own rear light has a setting for a simple pulse, AND a more complicated sequence - perhaps they should ALL feature this as standard :?: :idea:



Oh they still do ,Ernest - try using a digital camera on "video" mode on a TV, or your monitor and play it back.

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 Post subject:
PostPosted: Mon May 15, 2006 21:12 
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Indeed a problem. It's a condition which leads to recurrent seizures.

Did you know that one in two hundred suffer a form of this at some time in their lives?

Can be a couple of seconds of a blank look. We used to call it a "petit mal" ... person blinks a little and twitches.

Or what we call a "grand mal" ... staring and stiffening of the body with thrashing or even violent movements. Mouth may take on a blue tinge and it lasts for minutes - not seconds. Person feels weak and drowsy afterwards.

(some people have these in their sleep and never even know about it.. :shock: - If you have such an episode and no further episodes for at least 8 weeks .. you'll probably never ever have another one. ... why we stop them from driving on medical grounds for at least 6 months to one year following a reported fit of these types ..and yes .. the neurologists in this rather over -large family are correctly draconian in this. )

The full blown version of this very unfortunate affliction (it's not a disease and people who suffer from it are articulate, intelligent and with the correct treatment .. they lead normal and productive lives) - we call this "complex partial". The person suffers from a number of attacks and even has some warning signs.. plucking at clothes, agitation and some confused state and angst.

OK - so what is it?

I'll keep it in simple non-medic terms as people understand it better (and I do not intend that to be as patronising as it may sound to the more sensitive members... :wink: Am simply trying to explain in simplistic terms which anyone and everyone can understand - no point talking jargon .. as that makes us medics sound "pompous" - and I am most certainly not .. :lol: )

We all have electrical activityin the nerve cells within our brains .. why we get tired if we stare at a computer screen or TV for long periods (also why it can trigger latent epilepsy - the ine -off type in particular.) Someone who suffers from this condition have an abnormal electrical activity in the nerve cells within.

Most certainly the sufferer has some scarring to the brain .. bang on head, infection ( a lurgy which attacks the brain can cause this scarring of the nerve cells to occur) ..

These are the most common causes of the single "mals"

Brain tumours and strokes can also cause this.

We are still researching causes and so far we can only detect definite causes in around 30-40% of cases.

If anyone suffers any such "mal" - then your NHS Trust should run an EEG scam to measure the electrical activity of your brain. .. We may even run a CT scan - giving us a computerised detail of your brain. An MRI scan will give us a detailed image of brain tissues.. and blood tests will reveal other causes.. low blood sugar ..kidney/liver failure can also trigger this.


We only medicate with anti-convulsants if you have two or more "episodes" in rapid succession.

What I suggest is //

never look for long periods at any flashing light.. TV screen or computer screen.

Stretch your legs. Read a newspaper. Screw your eyes tightly - cover with hands and open slowly three times. This recharges them.

:wink:

Avoid becoming overtired.. relax .. chill out.

Eat and drink properly .. maintain a balanced diet with all your fave foods in moderation.

Make sure you eat and drink properly.. never indulge in any exercise - including gentle cycling and walking without proper "fuel".

Avoid anything which you know causes a headache .. and we all know some of us get headaches from too much sleep, wine, chocolate, certain foods and activities. Be aware of your SELF and your BODY.

Listen to your body as you do the car engine.

Listen to your body as you listen to fave music

Listen to your body as you listen out for dangers whilst on your bike.

Your body is your temple.. :wink:

Your brain - your control mechanism. :wink:

The engine management system :wink:

"

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PostPosted: Thu May 18, 2006 01:12 
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Basic fieldcraft teaches that the eye is good at picking up movement better than something stationary. I've two led lamps one on constant and the other on flashing so it is picked up on in the same way that movement is.

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