Permission from neighbours to bury cable

[aptsys]

Information displays using a multiplexed array of LED elements to display text or graphics can be made to appear up to 5 times brighter than an element would be it run at maximum constant current but the mark space ratio of the light from an individual element ( pixel ) would be as low as 1 ( ON ) to 10 ( OFF ) or even lower.

5x brighter? You're talking nonsense. I've worked on display systems and the only reason we multiplex is to simplify the drive circuitry, not for any perceived brightness changes. JohnW2 is correct - as soon as you have multiple elements multiplexed there is no perceived brightness change anyway. The effect you describe is only for a single PWM source where the eye is fooled into thinking something is brighter than it actually is. It also only applies to a relatively low (50-78Hz) frequencies which is several times lower than the PWM rate for a typical LED display.

 

[bernardgreen]

I've worked on display systems

I have designed display systems where limited power required over current pulsing to achieve a perceived inscrease in brighness. This was late 1970 using the TIL311

the only reason we multiplex is to simplify the drive circuitry,

That is the main reason when dealing with a large number of LED elements.

not for any perceived brightness changes.

Even when a display does not need a multiplexed drive system then pulses of over current do create a brighter perceived light and / or reduce power consumption for the same or higher level of perceived brightness

 

[aptsys]

Even when a display does not need a multiplexed drive system then pulses of over current do create a brighter perceived light and / or reduce power consumption for the same or higher level of perceived brightness

Only under a very specific set of circumstances with specific frequency and only on certain wavelengths. It has been shown the photoreceptor response isn't anything like what TI were claiming in their paper from the 70's so while the Talbot-Plateau Law is a proven phenomenon, it is not suitable for display systems unless the entire display is pulsed at low frequency. It can't be used in multiplexing.

 

[JohnW2]

5x brighter? You're talking nonsense. I've worked on display systems and the only reason we multiplex is to simplify the drive circuitry, not for any perceived brightness changes. JohnW2 is correct - as soon as you have multiple elements multiplexed there is no perceived brightness change anyway. The effect you describe is only for a single PWM source where the eye is fooled into thinking something is brighter than it actually is. It also only applies to a relatively low (50-78Hz) frequencies which is several times lower than the PWM rate for a typical LED display.

Indeed.

As I implied before, the one thing that presumably is true is that if one has N (not chronologically overlapping) multiplexed channels, each with a mark-space ratio of 1:N, then one will have constant (not pulsatile) light output, but can use current pulses of a magnitude that the LED elements would not survive if it were a continuous current?

However, I'm far from convinced that such an approach would achieve anything particularly useful. Once one has reached a stage at which current is flowing continuously through LEDs (albeit different LEDs at different points in time), I would have thought that one might just as well use a (probably smaller) number of LEDs which are powered continuously, but not beyond their continuous rating. Not only would that probably increase product life, but (in view of the slightly 'convex' shape of the light/current curve) I imagine that it could be more efficient (in terms of light/current, or light/power), couldn't it?

Kind Regards, John

 

[mattylad]

Gents, this is not helping the Op who wants to power his distant garage.

LED lights can flicker, thats all that need to be said - not having a dick measuring contest.

 

[JohnW2]

Gents, this is not helping the Op who wants to power his distant garage.

It's not. It arose because, as a cheaper (and less potentially problem-strewn) alternative to supplying mains power, it was suggested first that he should use a generator (which I think it what the OP decided to do), and then someone talked about cordless tools and rechargeable LED work lights (and bernard then mentioned the danger of 'flickering' lights - and the rest is 'history'!).

What has happened subsequently to this thread (subsequent to the OP leaving, back on page 2) is essentially a consequence of the inability of the forum's software to allow threads to be 'split' (easily or at all). If you don't want to read it, you obviously don't need to.

Kind Regards, John

 

[mattylad]

I suspect that the forums moderators do have the ability to split the thread, however do they want to? It's not going to do it automatically (I have never heard of any forum software that does that).
Perhaps if y'all keep things more on topic and started new threads where you can discuss the merits of LED lighting at length then people asking for help would not give up at page 2.

So it's not a consequence of anything to do with the forum software, more with the forum users who bicker about something else instead

 

[JohnW2]

I suspect that the forums moderators do have the ability to split the thread .....

I have responded to this message by starting a new thread ( click here ).

Kind Regards, John

 

[JohnW2]

Indeed. As I implied before, the one thing that presumably is true is that ....

In view of expressed unhappiness about this 'tangential discussion', I have started a new thread ( click here ), and would be grateful if any further posts on this topic could be made in that new thread. Thanks.

Kind Regards, John