EDAboard.com | EDAboard.de | EDAboard.co.uk | WTWH Media

LED car lights flicker - no need!

Ask a question - edaboard.com

elektroda.net NewsGroups Forum Index - Electronics - LED car lights flicker - no need!

Goto page Previous  1, 2, 3, ... 9, 10, 11  Next

DavidR
Guest

Tue Apr 23, 2013 8:09 pm   



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

Quote:
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.

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.

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

Major Scott
Guest

Tue Apr 23, 2013 8:39 pm   



On Tue, 23 Apr 2013 21:09:01 +0100, DavidR <dr6092_at_gmail.com> wrote:

Quote:
"Major Scott" <no_at_spam.com> wrote
On Tue, 23 Apr 2013 11:36:27 +0100, DavidR <dr6092_at_gmail.com> 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.

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.

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?

Dave Plowman
Guest

Tue Apr 23, 2013 11:09 pm   



In article <op.wvz5n4px2eh2io_at_red.lan>,
Major Scott <no_at_spam.com> wrote:
Quote:
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 dave_at_davesound.co.uk London SW 12

Major Scott
Guest

Tue Apr 23, 2013 11:17 pm   



On Wed, 24 Apr 2013 00:09:36 +0100, Dave Plowman <dave_at_davesound.co.uk> wrote:

Quote:
In article <op.wvz5n4px2eh2io_at_red.lan>,
Major Scott <no_at_spam.com> 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"

Major Scott
Guest

Tue Apr 23, 2013 11:20 pm   



On Wed, 24 Apr 2013 00:17:13 +0100, Major Scott <no_at_spam.com> wrote:

Quote:
On Wed, 24 Apr 2013 00:09:36 +0100, Dave Plowman <dave_at_davesound.co.uk> wrote:

In article <op.wvz5n4px2eh2io_at_red.lan>,
Major Scott <no_at_spam.com> 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 fuck did he think he was doing?!" -- Billy Connolly

Major Scott
Guest

Tue Apr 23, 2013 11:21 pm   



On Wed, 24 Apr 2013 00:09:36 +0100, Dave Plowman <dave_at_davesound.co.uk> wrote:

Quote:
In article <op.wvz5n4px2eh2io_at_red.lan>,
Major Scott <no_at_spam.com> 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"

Daniel47@teranews.com
Guest

Wed Apr 24, 2013 7:33 am   



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

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.

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

Daniel

Ian Jackson
Guest

Wed Apr 24, 2013 7:34 am   



In message <53411d7de7dave_at_davenoise.co.uk>, Dave Plowman
<dave_at_davesound.co.uk> writes
Quote:
In article <op.wvz5n4px2eh2io_at_red.lan>,
Major Scott <no_at_spam.com> 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

Dave Plowman
Guest

Wed Apr 24, 2013 8:54 am   



In article <op.wv0oip1h2eh2io_at_red.lan>,
Major Scott <no_at_spam.com> wrote:
Quote:
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 dave_at_davesound.co.uk London SW 12

Dave Plowman
Guest

Wed Apr 24, 2013 8:59 am   



In article <3sN4ACCMs4dRFwS6_at_g3ohx.demon.co.uk>,
Ian Jackson <ianREMOVETHISjackson_at_g3ohx.demon.co.uk> wrote:
Quote:
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.


Quote:
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 dave_at_davesound.co.uk London SW 12

DavidR
Guest

Wed Apr 24, 2013 9:05 am   



"Major Scott" <no_at_spam.com> wrote
Quote:

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.

Ian Jackson
Guest

Wed Apr 24, 2013 10:06 am   



In message
<2082196069388490010.841939%steve%-malloc.co.uk_at_news.eternal-september.or
g>, Steve Firth <%steve%@malloc.co.uk> writes
Quote:
Dave Plowman <dave_at_davesound.co.uk> wrote:
In article <op.wv0oip1h2eh2io_at_red.lan>,
Major Scott <no_at_spam.com> 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

Dave Plowman
Guest

Wed Apr 24, 2013 10:09 am   



In article
<2082196069388490010.841939%steve%-malloc.co.uk_at_news.eternal-september.org>,
Steve Firth <%steve%@malloc.co.uk> wrote:
Quote:
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 dave_at_davesound.co.uk London SW 12

Steve Firth
Guest

Wed Apr 24, 2013 11:55 am   



Dave Plowman <dave_at_davesound.co.uk> wrote:
Quote:
In article <op.wv0oip1h2eh2io_at_red.lan>,
Major Scott <no_at_spam.com> 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><|
_/ _/

Dave Plowman
Guest

Wed Apr 24, 2013 12:15 pm   



In article
<1453041046388492124.730151%steve%-malloc.co.uk_at_news.eternal-september.org>,
Steve Firth <%steve%@malloc.co.uk> wrote:
Quote:
Dave Plowman <dave_at_davesound.co.uk> wrote:
In article
2082196069388490010.841939%steve%-malloc.co.uk_at_news.eternal-september.org>,
Steve Firth <%steve%@malloc.co.uk> 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?

Quote:
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.

Quote:
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 dave_at_davesound.co.uk London SW 12

Goto page Previous  1, 2, 3, ... 9, 10, 11  Next

elektroda.net NewsGroups Forum Index - Electronics - LED car lights flicker - no need!

Ask a question - edaboard.com

Arabic version Bulgarian version Catalan version Czech version Danish version German version Greek version English version Spanish version Finnish version French version Hindi version Croatian version Indonesian version Italian version Hebrew version Japanese version Korean version Lithuanian version Latvian version Dutch version Norwegian version Polish version Portuguese version Romanian version Russian version Slovak version Slovenian version Serbian version Swedish version Tagalog version Ukrainian version Vietnamese version Chinese version Turkish version
EDAboard.com map