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LED car lights flicker - no need!

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Major Scott
Guest

Mon Apr 22, 2013 6:44 pm   



Surely they can design LED lights on cars to have a higher frequency PWM? Even 100K cars flicker dramatically, especially when filmed. It makes them look really cheap. All it would take is a higher frequency PWM, or a smoothing capacitor?

--
In 2005 eight Brits (All Scottish) cracked their skulls while throwing up into the toilet.

Dave Plowman
Guest

Tue Apr 23, 2013 10:10 am   



In article <kl5ibr$qiu$1_at_speranza.aioe.org>,
<neil_at_the.shed> wrote:
Quote:
On Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" <no_at_spam.com> wrote:
Surely they can design LED lights on cars to have a higher frequency
PWM= ? Even =A3100K cars flicker dramatically, especially when filmed.
It m= akes them look really cheap. All it would take is a higher
frequency PW= M, or a smoothing capacitor?

They flicker for a reason. If they smoothed the current they might just
as well use DC direct from the battery. I don't know the technical
reasons why but apparently using the equivalent DC voltage required to
get the same brightness as you can get by strobing them would burn them
out. I'm sure some electronics guru on here can explain more. But it
does lead to interesting effects on video as you say Surprised)

Pulsing an LED is a way of getting a higher light output from it without
overheating. Overheating an LED kills it in short order. Seeing a flicker
from them on a video is the same effect as wagon wheels appearing to turn
backwards on old cowboy and indian films - stroboscopic effect.

--
*WHY IS THERE AN EXPIRATION DATE ON SOUR CREAM?

Dave Plowman dave_at_davesound.co.uk London SW 12

DavidR
Guest

Tue Apr 23, 2013 10:36 am   



<neil_at_the.shed> wrote in message news:kl5ibr$qiu$1_at_speranza.aioe.org...
Quote:
On Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" <no_at_spam.com> wrote:
Surely they can design LED lights on cars to have a higher frequency PWM=
? Even =A3100K cars flicker dramatically, especially when filmed. It m=
akes them look really cheap. All it would take is a higher frequency PW=
M, or a smoothing capacitor?

They flicker for a reason. If they smoothed the current they might just as
well use DC direct from the battery. I don't know the technical reasons
why but

The effect relies on the persistance of the eyes to make it appear that the
average brightness is higher. Smoothing at source would be less energy
efficient.

Agreed the effect is not pleasant. It would help if they could introduce
softer start for indicators and brake light dimming when conditions suggest
a slow moving queue.


Guest

Tue Apr 23, 2013 10:56 am   



On Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" <no_at_spam.com> wrote:
Quote:
Surely they can design LED lights on cars to have a higher frequency PWM=
? Even =A3100K cars flicker dramatically, especially when filmed. It m=
akes them look really cheap. All it would take is a higher frequency PW=
M, or a smoothing capacitor?

They flicker for a reason. If they smoothed the current they might just as
well use DC direct from the battery. I don't know the technical reasons why but
apparently using the equivalent DC voltage required to get the same brightness
as you can get by strobing them would burn them out. I'm sure some electronics
guru on here can explain more. But it does lead to interesting effects on
video as you say Surprised)

NJR


Guest

Tue Apr 23, 2013 12:32 pm   



On Tue, 23 Apr 2013 11:10:27 +0100
Dave Plowman <dave_at_davesound.co.uk> wrote:
Quote:
Pulsing an LED is a way of getting a higher light output from it without
overheating. Overheating an LED kills it in short order. Seeing a flicker

Its odd though isn't it. The way they're constructed must mean the amount of
heat generated for a given voltage or current must slowly tail off so although
they'd heat up too much at constant voltage X you can pulse them at for
arguments sake X*2 producing the same or even more total light but without a
doubling of the heat generated so allowing for cooling down to safe levels
during the OFF periods of the pulse. Or something like that.

NJR

Major Scott
Guest

Tue Apr 23, 2013 2:34 pm   



On Tue, 23 Apr 2013 11:10:27 +0100, Dave Plowman <dave_at_davesound.co.uk> wrote:

Quote:
In article <kl5ibr$qiu$1_at_speranza.aioe.org>,
neil_at_the.shed> wrote:
On Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" <no_at_spam.com> wrote:
Surely they can design LED lights on cars to have a higher frequency
PWM= ? Even =A3100K cars flicker dramatically, especially when filmed.
It m= akes them look really cheap. All it would take is a higher
frequency PW= M, or a smoothing capacitor?

They flicker for a reason. If they smoothed the current they might just
as well use DC direct from the battery. I don't know the technical
reasons why but apparently using the equivalent DC voltage required to
get the same brightness as you can get by strobing them would burn them
out. I'm sure some electronics guru on here can explain more. But it
does lead to interesting effects on video as you say Surprised)

Pulsing an LED is a way of getting a higher light output from it without
overheating. Overheating an LED kills it in short order.

Take for example the brake/tail lights. These are often pulsed for tail and on for brake. So what you said doesn't make sense. Anything less than full voltage on (as for brake) will be lower heat.

Quote:
Seeing a flicker
from them on a video is the same effect as wagon wheels appearing to turn
backwards on old cowboy and indian films - stroboscopic effect.

It's way worse than that - the duty cycle is quite a lot less than 50%, so you see them off, with the occasional on.

--
Peter is listening to "Eagles - Hotel California"

Major Scott
Guest

Tue Apr 23, 2013 2:38 pm   



On Tue, 23 Apr 2013 11:36:27 +0100, DavidR <dr6092_at_gmail.com> wrote:

Quote:
neil_at_the.shed> wrote in message news:kl5ibr$qiu$1_at_speranza.aioe.org....
On Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" <no_at_spam.com> wrote:
Surely they can design LED lights on cars to have a higher frequency PWM>>> ? Even =A3100K cars flicker dramatically, especially when filmed. It m>>> akes them look really cheap. All it would take is a higher frequency PW>>> M, or a smoothing capacitor?

They flicker for a reason. If they smoothed the current they might just as
well use DC direct from the battery. I don't know the technical reasons
why but

The effect relies on the persistance of the eyes to make it appear that the
average brightness is higher.

Easy enough to double the frequency of the flicker, then you wouldn't notice it. Remember 50Hz CRT monitors?

Quote:
Smoothing at source would be less energy efficient.

I don't believe you. Switched mode power supplies are very cheap nowadays, especially compared with the cost of a car, especially a 100K car which has the same problem.

You can get a very smooth DC voltage of any level out of one - just look at your PC power supply then think of a smaller version of it. There are in fact smaller versions of it on your motherboard changing 12 volts to the CPU voltage (which is in fact variable).

Quote:
Agreed the effect is not pleasant. It would help if they could introduce
softer start for indicators

I prefer them to go on and off suddenly. The only problem I have is flickery tail lights.

Quote:
and brake light dimming when conditions suggest a slow moving queue.

I don't agree with different brightnesses of brakes. We already have two brightnesses of red - tail and brake. Adding more would just lead to confusion, you would wonder if it was a tail or a brake.

--
"It is generally inadvisable to eject directly over the area you just bombed." - U.S. Air Force Pilot training manual

Major Scott
Guest

Tue Apr 23, 2013 2:40 pm   



On Tue, 23 Apr 2013 09:56:27 +0100, <neil_at_the.shed> wrote:

Quote:
On Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" <no_at_spam.com> wrote:
Surely they can design LED lights on cars to have a higher frequency PWM=
? Even =A3100K cars flicker dramatically, especially when filmed. It m=
akes them look really cheap. All it would take is a higher frequency PW=
M, or a smoothing capacitor?

They flicker for a reason. If they smoothed the current they might just as
well use DC direct from the battery.

No, provide them with a lower DC voltage to make them dimmer. Say 12V for brake and 9V for tail.

Quote:
I don't know the technical reasons why but
apparently using the equivalent DC voltage required to get the same brightness
as you can get by strobing them would burn them out. I'm sure some electronics
guru on here can explain more. But it does lead to interesting effects on
video as you say Surprised)

So you're saying that on brake they are also strobed? I have never noticed a brake strobing. It's the tails that do it.

--
If vegetarians eat vegetables, what do humanitarians eat?

Dave Plowman
Guest

Tue Apr 23, 2013 3:58 pm   



In article <op.wvzz3ywg2eh2io_at_red.lan>,
Major Scott <no_at_spam.com> wrote:
Quote:
Pulsing an LED is a way of getting a higher light output from it
without overheating. Overheating an LED kills it in short order.

Take for example the brake/tail lights. These are often pulsed for tail
and on for brake. So what you said doesn't make sense. Anything less
than full voltage on (as for brake) will be lower heat.

LEDs are current, not voltage, driven.

--
*The best cure for sea sickness, is to sit under a tree.

Dave Plowman dave_at_davesound.co.uk London SW 12

Dave Plowman
Guest

Tue Apr 23, 2013 4:00 pm   



In article <op.wvz0doie2eh2io_at_red.lan>,
Major Scott <no_at_spam.com> wrote:
Quote:
They flicker for a reason. If they smoothed the current they might
just as well use DC direct from the battery.

No, provide them with a lower DC voltage to make them dimmer. Say 12V
for brake and 9V for tail.

I'd suggest you look up the Ladybird book of electronics to get a clue
about how LEDs work.

--
*Pride is what we have. Vanity is what others have.

Dave Plowman dave_at_davesound.co.uk London SW 12

Major Scott
Guest

Tue Apr 23, 2013 4:33 pm   



On Tue, 23 Apr 2013 16:01:43 +0100, <neil_at_the.shed> wrote:

Quote:
On Tue, 23 Apr 2013 15:40:26 +0100
"Major Scott" <no_at_spam.com> wrote:
No, provide them with a lower DC voltage to make them dimmer. Say 12V for
brake and 9V for tail.

So you want tail lights made dimmer? Oh, ok.

Next...

Tail lights ARE dimmer than brakes. Traditionally 5W of incandescent for tail and 21W for brakes.

I'm just suggesting the dimness should be created in a different manner. Either the PWM has a higher frequency, or provide smooth DC at a lower voltage than that to create 21W equivalent.

--
The squaw on the hippopotamus is equal to the sons of the squaws on the other two hides!

Major Scott
Guest

Tue Apr 23, 2013 4:34 pm   



On Tue, 23 Apr 2013 16:58:35 +0100, Dave Plowman <dave_at_davesound.co.uk> wrote:

Quote:
In article <op.wvzz3ywg2eh2io_at_red.lan>,
Major Scott <no_at_spam.com> wrote:
Pulsing an LED is a way of getting a higher light output from it
without overheating. Overheating an LED kills it in short order.

Take for example the brake/tail lights. These are often pulsed for tail
and on for brake. So what you said doesn't make sense. Anything less
than full voltage on (as for brake) will be lower heat.

LEDs are current, not voltage, driven.

When there's a series resistor, then you can think of them as voltage driven. Anyway electronics to lower the current can be made without pulsing.

--
When shagging a goat you are best taking it to the edge of a cliff because they push back harder. -- Billy Connelly

Major Scott
Guest

Tue Apr 23, 2013 4:35 pm   



On Tue, 23 Apr 2013 17:00:08 +0100, Dave Plowman <dave_at_davesound.co.uk> wrote:

Quote:
In article <op.wvz0doie2eh2io_at_red.lan>,
Major Scott <no_at_spam.com> wrote:
They flicker for a reason. If they smoothed the current they might
just as well use DC direct from the battery.

No, provide them with a lower DC voltage to make them dimmer. Say 12V
for brake and 9V for tail.

I'd suggest you look up the Ladybird book of electronics to get a clue
about how LEDs work.

See my other reply as you've just said the same thing again.

--
Is it true that DNA stands for the National Dyslexia Association?

Major Scott
Guest

Tue Apr 23, 2013 4:40 pm   



On Tue, 23 Apr 2013 17:00:08 +0100, Dave Plowman <dave_at_davesound.co.uk> wrote:

Quote:
In article <op.wvz0doie2eh2io_at_red.lan>,
Major Scott <no_at_spam.com> wrote:
They flicker for a reason. If they smoothed the current they might
just as well use DC direct from the battery.

No, provide them with a lower DC voltage to make them dimmer. Say 12V
for brake and 9V for tail.

I'd suggest you look up the Ladybird book of electronics to get a clue
about how LEDs work.

Here's some people discussing the same problem with torches:
http://www.candlepowerforums.com/vb/showthread.php?268122-Do-you-like-PWM-(pulse-width-modulation)-controlled-lights

And here, which mentions badly designed tail lights on Cadillacs:
http://www.nlvocables.com/blog/?p=188

And more complaints about pathetic car lights:
http://budgetlightforum.com/node/18967

For crying out loud, just increase the frequency if you're too much of a cheapskate to have a current controller in a car that cost 10s of thousands of pounds.

--
Is it true that DNA stands for the National Dyslexia Association?


Guest

Tue Apr 23, 2013 5:01 pm   



On Tue, 23 Apr 2013 15:40:26 +0100
"Major Scott" <no_at_spam.com> wrote:
Quote:
No, provide them with a lower DC voltage to make them dimmer. Say 12V for
brake and 9V for tail.

So you want tail lights made dimmer? Oh, ok.

Next...

NJR

Goto page 1, 2, 3 ... 9, 10, 11  Next

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