Pulsing an LED is a way of getting a higher light output from it withoutOn Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" <no@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)
The effect relies on the persistance of the eyes to make it appear that the
They flicker for a reason. If they smoothed the current they might just as
)Its odd though isn't it. The way they're constructed must mean the amount of
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.In article <kl5ibr$qiu$1@speranza.aioe.org>,
neil@the.shed> wrote:
On Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" <no@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
Pulsing an LED is a way of getting a higher light output from it without
overheating. Overheating an LED kills it in short order.
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.
Easy enough to double the frequency of the flicker, then you wouldn't notice it. Remember 50Hz CRT monitors?
I don't believe you. Switched mode power supplies are very cheap nowadays, especially compared with the cost of a car, especially a Ł100K car which has the same problem.
I prefer them to go on and off suddenly. The only problem I have is flickery tail lights.
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.
No, provide them with a lower DC voltage to make them dimmer. Say 12V for brake and 9V for tail.
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.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
LEDs are current, not voltage, driven.
I'd suggest you look up the Ladybird book of electronics to get a clue
Tail lights ARE dimmer than brakes. Traditionally 5W of incandescent for tail and 21W for brakes.
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.
See my other reply as you've just said the same thing again.
Here's some people discussing the same problem with torches:
So you want tail lights made dimmer? Oh, ok.
What is generated
If you can't maintain a gap in a slow moving queue without the help of brake
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? Ł4. That's the LEDs, the housing, and the electronics. So car makers have absolutely no excuse.
What? I'm the one that DOESN'T want more lights.
Why would you have a 'series resistor' if they are pulse driven?
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.