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.

On Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" 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 )

NJR

In article ,
wrote:
On Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" 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 )

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 London SW 12

On Tue, 23 Apr 2013 11:10:27 +0100
Dave Plowman 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. 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

wrote in message ...
On Tue, 23 Apr 2013 11:10:27 +0100
Dave Plowman 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. 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.

LEDs can be pulsed close to the limit for the bond wires - but only for very
low duty cycle, a short time on and (relatively) long time off allows
cooling between pulses.

being pulsed very rapidly, you're not aware of the interruptions
(persistence of vision) so the perceived brightness is much brighter than
you'd get for the equivalent average current.

On Tue, 23 Apr 2013 11:10:27 +0100, Dave Plowman wrote:

In article ,
wrote:
On Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" 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 )

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.

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"

In article ,
Major Scott 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.

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

Dave Plowman London SW 12

On Tue, 23 Apr 2013 16:58:35 +0100, Dave Plowman wrote:

In article ,
Major Scott 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

"Dave Plowman" wrote in message
...
In article ,
Major Scott 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.

I'm sort of wondering how that holds up with the typical example of a
current controlled buck converter.

Certainly you have the series current sense resistor fed to the fb input of
the controller - but there's usually the catch diode behind the inductor,
which as in any buck routes the collapsing field energy through the LED.

On Tue, 23 Apr 2013 11:10:27 +0100, Dave Plowman wrote:

In article ,
wrote:
On Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" 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 )

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.

The front LED running lights don't even flicker on camera. And I don't think brakes do either. So why make the tails any different? They're made up of many LEDs, so just power up less of them (which I've seen buses doing) for tail and all of them for brake.

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

wrote in message ...
On Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" 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.

On Tue, 23 Apr 2013 11:36:27 +0100, DavidR wrote:

wrote in message ....
On Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" 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?

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).

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.

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" wrote
On Tue, 23 Apr 2013 11:36:27 +0100, DavidR wrote:

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?

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.

What is generated
------ ------
| | | |
| |______| |_____

What the eye perceives
-------- --------
| \ | \
| \___| \____

By averaging the power in the top waveform, the peak intensity is reduced
and would not use eye's ability to fill in the gaps. Therefore a
smooth waveform requires more power at source.

Picking a Cree led at random, the data sheet shows that the increase in
luminous output falls relative to the increase in current (ie, doubling the
current produces less than a doubling of output), so at first sight it would
seem that pulsing is counterproductive. Which means that there are other
factors that make it advantageous.

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.

If you can't maintain a gap in a slow moving queue without the help of brake
lights, are you sure you're competent?

On Tue, 23 Apr 2013 21:09:01 +0100, DavidR wrote:

"Major Scott" wrote
On Tue, 23 Apr 2013 11:36:27 +0100, DavidR wrote:

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?

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.

What is generated
------ ------
| | | |
| |______| |_____

What the eye perceives
-------- --------
| \ | \
| \___| \____

By averaging the power in the top waveform, the peak intensity is reduced
and would not use eye's ability to fill in the gaps. Therefore a
smooth waveform requires more power at source.

Picking a Cree led at random, the data sheet shows that the increase in
luminous output falls relative to the increase in current (ie, doubling the
current produces less than a doubling of output), so at first sight it would
seem that pulsing is counterproductive. Which means that there are other
factors that make it advantageous.

I've got some GU10 spots in this room, powered off the mains, with three CREE LEDs in each. They produce the equivalent of 50W apparently (using 6W of electricity), but they look brighter to me than a 50W halogen, I'd say more like 75W. They are perfectly smooth, no flicker, so it can be done easily. And the cost of these things? £4. That's the LEDs, the housing, and the electronics. So car makers have absolutely no excuse.

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.

If you can't maintain a gap in a slow moving queue without the help of brake
lights, are you sure you're competent?

What? I'm the one that DOESN'T want more lights.

--
If a cat joined the Red Cross, would it become a First-Aid Kit?

On Tue, 23 Apr 2013 09:56:27 +0100, wrote:

On Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" 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.

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 )

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?

On Tue, 23 Apr 2013 15:40:26 +0100
"Major Scott" 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...

NJR

On Tue, 23 Apr 2013 16:01:43 +0100, wrote:

On Tue, 23 Apr 2013 15:40:26 +0100
"Major Scott" 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!

In article ,
Major Scott 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.

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

Dave Plowman London SW 12

On Tue, 23 Apr 2013 17:00:08 +0100, Dave Plowman wrote:

In article ,
Major Scott 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?

On Tue, 23 Apr 2013 17:00:08 +0100, Dave Plowman wrote:

In article ,
Major Scott 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/...trolled-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?