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 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 11:10:27 +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"

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

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

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

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 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!

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

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?

"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?

In article ,
Major Scott wrote:
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.

Why would you have a 'series resistor' if they are pulse driven?

But in any case it is irrelevant. It's the current they are driven with
that matters - not the voltage.

--
*How much deeper would the oceans be without sponges? *

Dave Plowman London SW 12

On Wed, 24 Apr 2013 00:09:36 +0100, Dave Plowman wrote:

In article ,
Major Scott wrote:
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.

Why would you have a 'series resistor' if they are pulse driven?

But in any case it is irrelevant. It's the current they are driven with
that matters - not the voltage.

One is related to the other. If you stick a million volts on the LED you'll get a huge amount of current and it'll blow up. If you stick 0.5 volts on it you'll get no current flowing.

--
"One dies in Istanbul suicide attack"

On Wed, 24 Apr 2013 00:17:13 +0100, Major Scott wrote:

On Wed, 24 Apr 2013 00:09:36 +0100, Dave Plowman wrote:

In article ,
Major Scott wrote:
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.

Why would you have a 'series resistor' if they are pulse driven?

But in any case it is irrelevant. It's the current they are driven with
that matters - not the voltage.

One is related to the other. If you stick a million volts on the LED you'll get a huge amount of current and it'll blow up. If you stick 0.5 volts on it you'll get no current flowing.

Anyway, this is semantics. The point is you could get less flicker by having a higher duty cycle at a lower current, or by doubling the frequency of the pulses. Or just use a current limiter circuit and give it a constant current. Ok you might need better LEDs seen as they seem to be using crappy ones and making them appear brighter than they are by attempting to fool the eye and failing.

--
"I wonder who discovered we could get milk from cows and what the **** did he think he was doing?!" -- Billy Connolly

On Wed, 24 Apr 2013 00:09:36 +0100, Dave Plowman wrote:

In article ,
Major Scott wrote:
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.

Why would you have a 'series resistor' if they are pulse driven?

But in any case it is irrelevant. It's the current they are driven with
that matters - not the voltage.

If this pulsing can make them appear brighter than they are, why don't they use it in domestic LED bulbs?

--
"One dies in Istanbul suicide attack"

Major Scott wrote:
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.

No, the series resistor merely determines the maximum current that could
flow through the LED.

Daniel

In message , Dave Plowman
writes
In article ,
Major Scott wrote:
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.

Why would you have a 'series resistor' if they are pulse driven?

But in any case it is irrelevant. It's the current they are driven with
that matters - not the voltage.

Nothing is really only 'current driven'. It's more correct to say that
LEDs need to be driven from a power source which provides a fairly
well-defined current. Even when you drive them with pulsed current, the
amplitude of the pulses will be determined by the voltage producing the
pulses. At any instant, the power dissipated in the LED is simply the
product of the voltage across it (typically 2V, depending on the colour)
and the current flowing through it. When pulsed, the average power is
also determined by the mark-space ratio of the pulses.
--
Ian

In article ,
Major Scott wrote:
But in any case it is irrelevant. It's the current they are driven with
that matters - not the voltage.

If this pulsing can make them appear brighter than they are, why don't
they use it in domestic LED bulbs?

No idea. They are crap and I wouldn't have one in the house.

--
*I don't suffer from insanity -- I'm a carrier

Dave Plowman London SW 12

In article ,
Ian Jackson wrote:
Nothing is really only 'current driven'. It's more correct to say that
LEDs need to be driven from a power source which provides a fairly
well-defined current.

Very well defined if you're driving them hard. The source voltage is
irrelevant. Provided it is more than the forward voltage drop of the LED
or LED chain.


Even when you drive them with pulsed current, the
amplitude of the pulses will be determined by the voltage producing the
pulses. At any instant, the power dissipated in the LED is simply the
product of the voltage across it (typically 2V, depending on the colour)
and the current flowing through it. When pulsed, the average power is
also determined by the mark-space ratio of the pulses.

As I said, it's the current flow through the LED that you design for.

--
*Why do overlook and oversee mean opposite things?

Dave Plowman London SW 12

"Major Scott" wrote

If this pulsing can make them appear brighter than they are, why don't
they use it in domestic LED bulbs?

Because a large number of morons in and around the motor industry have
become attached to the idea that if some lighting is good, brighter lights
must be better.

Thy don't seem to recognise that the the current standard of lighting is
making the roads more dangerous.

Dave Plowman wrote:
In article ,
Major Scott wrote:
But in any case it is irrelevant. It's the current they are driven with
that matters - not the voltage.

If this pulsing can make them appear brighter than they are, why don't
they use it in domestic LED bulbs?

No idea. They are crap and I wouldn't have one in the house.

The LED bulbs I have used have been anything but "crap". They use 1/10th
the electricity of equivalent halogen bulbs and can be bought as flood or
spotlight versions.

--
€¢DarWin|
_/ _/

In message

g, Steve Firth writes
Dave Plowman wrote:
In article ,
Major Scott wrote:
But in any case it is irrelevant. It's the current they are driven with
that matters - not the voltage.

If this pulsing can make them appear brighter than they are, why don't
they use it in domestic LED bulbs?

No idea. They are crap and I wouldn't have one in the house.

The LED bulbs I have used have been anything but "crap". They use 1/10th
the electricity of equivalent halogen bulbs and can be bought as flood or
spotlight versions.

I was under the impression that they did use a pulsed supply in domestic
lighting.
--
Ian

In article
,
Steve Firth wrote:
No idea. They are crap and I wouldn't have one in the house.

The LED bulbs I have used have been anything but "crap". They use 1/10th
the electricity of equivalent halogen bulbs and can be bought as flood or
spotlight versions.

They may well use less electricity. But if that's the only criterion for
domestic lighting a fluorescent tube will do the job rather better and for
less cost.

--
*IS THERE ANOTHER WORD FOR SYNONYM?

Dave Plowman London SW 12

Dave Plowman wrote:
In article
,
Steve Firth wrote:
No idea. They are crap and I wouldn't have one in the house.

The LED bulbs I have used have been anything but "crap". They use 1/10th
the electricity of equivalent halogen bulbs and can be bought as flood or
spotlight versions.

They may well use less electricity. But if that's the only criterion for
domestic lighting a fluorescent tube will do the job rather better and for
less cost.

Where did I say it was the only criterion? The major objection from SWMBO
is that they are "too bright".

Way better than CFL and, as I mentioned, equivalent to halogen, in fact a
3W LED with SMD elements providers better illumination than a 35W halogen.

--
€¢DarWin|
_/ _/

On Wed, 24 Apr 2013 09:59:22 +0100
Dave Plowman wrote:
As I said, it's the current flow through the LED that you design for.

Look what article appeared on Slashdot today:

http://tech.slashdot.org/story/13/04...iency-droop-fi
nally-revealed

NJR

In article
,
Steve Firth wrote:
Dave Plowman wrote:
In article
,
Steve Firth wrote:
No idea. They are crap and I wouldn't have one in the house.

The LED bulbs I have used have been anything but "crap". They use
1/10th the electricity of equivalent halogen bulbs and can be bought
as flood or spotlight versions.

They may well use less electricity. But if that's the only criterion
for domestic lighting a fluorescent tube will do the job rather better
and for less cost.

Where did I say it was the only criterion?

It's the first thing you mentioned about them?

The major objection from
SWMBO is that they are "too bright".

Typically yes - when you look at them. Sadly the actual usable light from
them is anything but.

Way better than CFL and, as I mentioned, equivalent to halogen, in fact
a 3W LED with SMD elements providers better illumination than a 35W
halogen.

Define better. That usually means the latest thing to impress the gullible.

There are no LEDs on the domestic market that come even close to matching
the quality of light from halogen. Of course that doesn't much matter to
many.

--
*I want it all and I want it delivered

Dave Plowman London SW 12

Dave Plowman wrote:
In article
,
Steve Firth wrote:
Dave Plowman wrote:
In article
,
Steve Firth wrote:
No idea. They are crap and I wouldn't have one in the house.

The LED bulbs I have used have been anything but "crap". They use
1/10th the electricity of equivalent halogen bulbs and can be bought
as flood or spotlight versions.

They may well use less electricity. But if that's the only criterion
for domestic lighting a fluorescent tube will do the job rather better
and for less cost.

Where did I say it was the only criterion?

It's the first thing you mentioned about them?

The major objection from
SWMBO is that they are "too bright".

Typically yes - when you look at them. Sadly the actual usable light from
them is anything but.

Way better than CFL and, as I mentioned, equivalent to halogen, in fact
a 3W LED with SMD elements providers better illumination than a 35W
halogen.

Define better. That usually means the latest thing to impress the gullible.

There are no LEDs on the domestic market that come even close to matching
the quality of light from halogen. Of course that doesn't much matter to
many.

I love the way your opinion masquerades as fact.

--
€¢DarWin|
_/ _/

In article
,
Steve Firth wrote:
There are no LEDs on the domestic market that come even close to
matching the quality of light from halogen. Of course that doesn't
much matter to many.

I love the way your opinion masquerades as fact.

Then publish some plots of their spectrum that proves me wrong. I'll not
hold my breath.

--
*i souport publik edekashun.

Dave Plowman London SW 12

On Wed, 24 Apr 2013 08:33:48 +0100, wrote:

Major Scott wrote:
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.

No, the series resistor merely determines the maximum current that could
flow through the LED.

Take for example a 6 volt DC supply connected to an LED in series with a 200 ohm resistor.
2V 20mA at the LED, 4V 20mA in the resistor.

Now change the supply to 4V.
2V 10mA at the LED, 2V 10mA in the resistor.

Lowering voltage will dim the LED.

--
Did you hear about the new instant lottery game in India?
You scratch the ticket and if the dot matches the one on your forehead, you win a convenience store in the US.

On Wed, 24 Apr 2013 10:05:18 +0100, DavidR wrote:

"Major Scott" wrote

If this pulsing can make them appear brighter than they are, why don't
they use it in domestic LED bulbs?

Because a large number of morons in and around the motor industry have
become attached to the idea that if some lighting is good, brighter lights
must be better.

Thy don't seem to recognise that the the current standard of lighting is
making the roads more dangerous.

Some xenon headlights, yes. But LED brakelights are not too bright. They're just too flickery. They appear the same brightness as a standard 21W brakelight bulb to me.

So why can't this pretend brightness be applied to domestic lighting? An LED lamp which currently equates to a 50W incandescent could give out what looks like 100W. If it's not done because people are more likely to notice the flicker at home, then why not have a higher pulse frequency?

--
If it's zero degrees outside today and it's supposed to be twice as cold tomorrow, how cold is it going to be?

On Wed, 24 Apr 2013 09:54:44 +0100, Dave Plowman wrote:

In article ,
Major Scott wrote:
But in any case it is irrelevant. It's the current they are driven with
that matters - not the voltage.

If this pulsing can make them appear brighter than they are, why don't
they use it in domestic LED bulbs?

No idea. They are crap and I wouldn't have one in the house.

Have you ever seen a CREE LED? I've got a load of GU10 CREE LED spots and they're better than the 50W halogens they replaced. 6W in, 50W out, and to my eyesight they look more like 75W out, and a whiter light too. And they don't keep tripping the circuit breaker when they go, or making the fitting to hot to touch which is worrying next to a wood panelled ceiling.

--
I went to San Francisco. I found someone's heart.

"Major Scott" wrote in message
news
On Wed, 24 Apr 2013 08:33:48 +0100,
wrote:

Major Scott wrote:
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.

No, the series resistor merely determines the maximum current that could
flow through the LED.

Take for example a 6 volt DC supply connected to an LED in series with a
200 ohm resistor.
2V 20mA at the LED, 4V 20mA in the resistor.

Now change the supply to 4V.
2V 10mA at the LED, 2V 10mA in the resistor.

**** a duck, they DID teach you something.

On Wed, 24 Apr 2013 11:06:50 +0100, Ian Jackson wrote:

In message

g, Steve Firth writes
Dave Plowman wrote:
In article ,
Major Scott wrote:
But in any case it is irrelevant. It's the current they are driven with
that matters - not the voltage.

If this pulsing can make them appear brighter than they are, why don't
they use it in domestic LED bulbs?

No idea. They are crap and I wouldn't have one in the house.

The LED bulbs I have used have been anything but "crap". They use 1/10th
the electricity of equivalent halogen bulbs and can be bought as flood or
spotlight versions.

I was under the impression that they did use a pulsed supply in domestic
lighting.

If they do then it's a much higher frequency. Some old cheap ones I've got have a definite flicker, but that's mains flicker (I looked inside one I accidentally dropped from the loft through the hatch onto wood flooring and smashed it and found simply a bridge rectifier, a capacitor, and a couple of resistors, with 50 tiny LEDs in series).

The decent CREE ones I've got have zero flicker. Here's one that expired and I opened to show Ian Field the circuit a month or three ago if you want to try to work out what it does:
http://petersphotos.com/temp/cree%20circuit.jpg I don't have it anymore it's gone in the bin.

--
Interesting fact number 476:
80% of millionaires drive used cars.

On Wed, 24 Apr 2013 20:36:32 +0100, bm wrote:


"Major Scott" wrote in message
news
On Wed, 24 Apr 2013 08:33:48 +0100,
wrote:

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

In article ,
Major Scott wrote:




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.

No, the series resistor merely determines the maximum current that could
flow through the LED.

Take for example a 6 volt DC supply connected to an LED in series with a
200 ohm resistor.
2V 20mA at the LED, 4V 20mA in the resistor.

Now change the supply to 4V.
2V 10mA at the LED, 2V 10mA in the resistor.

**** a duck, they DID teach you something.

I have a ****ing degree in it (not that it gets you a job).

--
Basketball analyst: "He dribbles a lot and the opposition doesn't like it. In fact you can see it all over their faces."