Multiplexing in displays of LED pixels is necessary to minimise the number of drivers needed but it is also used to "increase" the perceived brightness of some vehicle lights.
Permission from neighbours to bury cable
- Thread starter twills805
- Start date
Sponsored Links
I don't doubt that this is true.
However, am I not right in saying that (assuming the pulses in the various multiplexed channels do not overlap chronologically) multiplexing, per se, will have the effect of reducing the pulsatile nature of the light output of the LED array as a whole - and, indeed, that if one got the number of multiplexed channels and their timings 'just right' (in relation to the mark/space ratio of the pulses in any of them), then it would be theoretically possible to totally eliminate the pulsatile nature of that light output (of the array of LEDs as a whole)?
Kind Regards, John
Single "spot"of light.
The pulsatile nature of that light output can be minimised when using a multiplexed array of LED elements to create a single source of light that appears to be brighter than the sum of the brightnesses of the individual elements when driven by maximum constant current.
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.
Yes, I understand all that.
However, as I said/asked. does not multiplexing reduce the pulsatile nature of the light output? In the 'ultimate' case, taking your example of a 1:10 mark:space ratio, if one had 10 multiplexed channels (with no overlapping of the 'marks'), would the light output of the LED array then not theoretically be non-pulsatile (as well as, as you say, apparently much brighter than would be the case without 'pulsing')?
Kind Regards, John
Sponsored Links
- Joined
- 11 Jan 2004
- Messages
- 42,700
- Reaction score
- 2,629
- Country
That's obvious. They're for sawing tables with.
As you will be aware, all LED emitters need some form of current control. This is likely to be a simple buck or boost (depending on battery and emitter voltages) switch mode converter - even a really simple relaxation regulator. Such a converter can be made a lot simpler (ie cheaper) if you just don't bother about smoothing - so how much effort (ie cost) do you think goes into.most of them !
As I keep asking, even in cheap, battery-operated, lights??
Maybe things have changed, but what I've often seen in cheap battery-operated lights is the LED elements strung together in series string(s), such that the total Vf was quite close to the battery voltage, and then with just a single resistor limiting the current (but dissipating very little) - and a resistor is always going to be cheaper than even the cheapest and nastiest of SMPSUs!
Kind Regards, John
There are LED elements that have a semi-conductor resistor diffused into the element.
These elements can be connected directly to a voltage source, typically 3 volts from a pair of 1.5 volt batteries enabling long strings of low power LEDs lights to be easily manufactured.
These elements can be connected directly to a voltage source, typically 3 volts from a pair of 1.5 volt batteries enabling long strings of low power LEDs lights to be easily manufactured.
Yes, I'm aware of them (and, in fact, have some), but that doesn't really answer any of the questions I asked.
By pure co-incidence, I'm probably about to start a 'related' thread about an issue (which somewhat intrigues me) which has just arisen due to my 'checking' some of my 'Christmas Lights' in anticipation of the upcoming festive season - watch this space.
Kind Regards, John
Well yes, the answer is always going to be "it depends". But I'd be "not at all surprised" if something like a portable workshop light actually had a CC driver in it.
I agree, but the cheaper the product, the more surprised I'd be.
Those who produce very cheap products are probably more concerned that they are very cheap than about the apparent brightness.
Of course, it's totally different with main-powered (or battery- or mains-powered) ones. Since they (presumably) need a SMPSU of some sort, there is no reason why they shouldn't take the opportunity to enjoy the 'advantages' (in terms of apparent brightness) that can result from the sort of 'over-driven pulses' that we've been talking about.
Kind Regards, John
Actually, mains powered LEDs have less need for an SMPSU since the voltage is high (allowing many LEDs in series if needed and still headroom for a current control impedance) and the voltage relatively stable. So for a non-dimable mains LED, just an R, C, L, or some combination is all that's needed.
Of course, that does mean 100Hz flicker is very pronounced.
Of course, that does mean 100Hz flicker is very pronounced.
True. In fact, most of the LED bulbs/'lamps' (BC, ES etc. - NOT 'work lamps'
) have taken apart (particularly the cheaper ones) have had just a bridge rectifier and a capacitor.Kind Regards, John
- Joined
- 26 Aug 2016
- Messages
- 6,833
- Reaction score
- 1,010
- Country
this is very topical because I just discarded a cheap work light because it had terrible flicker and a very bad mark-space ratio. The replacements (osram ledvance) were hardly more expensive and they do vary brightness a bit but not to such an on-off extent (and they are a lot more efficient too)
The BC philips several watt incandescent substitute lamps we use throughout the house don't seem to have any perceptible flicker (based on my waving a bit of speedfit pipe in front of them)
The BC philips several watt incandescent substitute lamps we use throughout the house don't seem to have any perceptible flicker (based on my waving a bit of speedfit pipe in front of them)
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
