Dimmable LED lighting system?

As above, few "quality" systems do this because it alters the colour slightly.

The colour depends on the phosphor used to convert the UV from the LED junction into visible light. Maybe a change of temperature could affect the phosphor and the colour of the light it produces

You are missing out the constant current LED lamps used in many "professional grade" systems.

I am aware that many "lamps" that are just an LED element in a housing can be connected in series and fed from a single current source. But as you say these are ( for the most part ) "professional grade" and would be outside the comfort zone of the average DIYer.
 
Sponsored Links
.... If the current is reduced, most LEDs change colour to some extent. That is one reason why dimming is more normally done by pulse width modulation (PWM) - switching the LED between off and full normal current rapidly. Many driver circuits also use PWM for the basic current regulation - adjusting the on-off ratio to give the desired average current. That's why you can often see strobing effects from LEDs.
As above, few "quality" systems do this [dim by reducing current] because it alters the colour slightly.
I'm a little confused. As has often been discussed here, it seems that the physiology of light perception is such that the brightness of pulsed light from an LED will usually be perceived as much brighter than would be the case if the same average current were flowing continuously, in some cases maybe to the extent that the perceived brightness approaches the brightness of the individual pulses.

Hence, whilst one can understand how PWM can works effectively with incandescent bulbs, it would seem not to be a particularly effective way of dimming LEDs, since physiology would be attempting to 'resist' the dimming in the latter case.

Kind Regards, John
 
I'm a little confused. As has often been discussed here, it seems that the physiology of light perception is such that the brightness of pulsed light from an LED will usually be perceived as much brighter than would be the case if the same average current were flowing continuously, in some cases maybe to the extent that the perceived brightness approaches the brightness of the individual pulses.

Hence, whilst one can understand how PWM can works effectively with incandescent bulbs, it would seem not to be a particularly effective way of dimming LEDs, since physiology would be attempting to 'resist' the dimming in the latter case.

Kind Regards, John
This is what we found in University, we were given an exercise, using a 555 timer we would over drive so net power was same, the LED's seemed brighter, however the lux meter showed no change.
 
As for the cable losses themselves (i.e. assuming zero 'conversion losses'), distributing at, say, 48V rather than 230V would result in something like 4.8 times the current, hence about 23 times the power loss in a cable of the same CSA, or probably in excess of 100 times the power loss if one were comparing CAT5/6 (I think ~0.2mm² CSA) with, say, 1mm² T+E.
As already mentioned, there are 4 wires (minimum) for PoE - the later standards allow use of all 4 pairs for power (but not in 802.3af and 802.3at currently in use for such things).
EDIT: Not to mention that each device is supplied by it's own cable - so while each cable may be smaller, it's also only supplying one device. A bit like going back to the days of "one fuse, one radial, one socket" :whistle:
Yes, as with any sort oif 'automation', the opportunities for 'playing' would be endless, but probably more by way of gimmicks than truly 'useful' (let alone actually 'needed') functionality!
Yes, one man's feature is another man's (or woman's) gimmick. Myself and SWMBO tend to have differences of opinion even over simple things like whether to have a dimmer for the main living room lamps :whistle:

My son read about all the advances in central heating, and how running a LAN outlet to the TRV head would allow one to control each room individually. He installed a server in the loft and LAN outlets by each radiator. However when he came to install the TRV heads he found they were nearly all wifi
Indeed. Unfortunately the vast majority of people dislike the idea of running cables and insist on the much inferior wireless connections :mad: Mother was looking at a new build, and commenting on the absence of any provision for phone or data I got the reply (from the penny pinching developer who wouldn't even put in ducting for phone lines while it would have been easy to do) that "everything's wireless these days" :evil:
Doesn't help that new builds seem to be designed to be un-maintainable (partly due to building regs) - having done away with easily lifted floor boards in favour of large sheets of "weetabix" glued together and to the joists.
I will guess we will find the same with lighting
Sadly yes, a lot of stuff will be wireless with all the problems that brings.

The colour depends on the phosphor used to convert the UV from the LED junction into visible light. Maybe a change of temperature could affect the phosphor and the colour of the light it produces
With a quick search, I came across this document that discusses the changes and reasons.
I am aware that many "lamps" that are just an LED element in a housing can be connected in series and fed from a single current source. But as you say these are ( for the most part ) "professional grade" and would be outside the comfort zone of the average DIYer.
Not sure about being out of scope for DIY - many of them come as "plug together" kits that are easier to wire than using long strips where you have to solder the connections or remember to buy the little connectors.

Hence, whilst one can understand how PWM can works effectively with incandescent bulbs, it would seem not to be a particularly effective way of dimming LEDs, since physiology would be attempting to 'resist' the dimming in the latter case.
Well I can assure you that it's the standard method of dimming in most applications - partly for the colour rendering aspects mentioned. It's also a lot easier to do, and more efficient, in terms of electronics - just needing a power switch without need for heavy heatsinking.
 
Sponsored Links
EDIT: Not to mention that each device is supplied by it's own cable - so while each cable may be smaller, it's also only supplying one device. A bit like going back to the days of "one fuse, one radial, one socket" :whistle:
True, but the cable between switch and light is also generally only supply power to one light even with 230V and 1mm T+E.
Yes, one man's feature is another man's (or woman's) gimmick.
Indeed so, and one has to remember that the majority of technological 'features' which have come to be taken for granted are in no way 'needed' - but that doesn't alter the fact taht some will regard them as 'gimmicks' :)
Well I can assure you that it's the standard method of dimming in most applications - partly for the colour rendering aspects mentioned. It's also a lot easier to do, and more efficient, in terms of electronics - just needing a power switch without need for heavy heatsinking.
Dunno. It has certainly (and with good reason) been the norm for dimming of incandescent lamps - indeed, even standard ubiquitous 'analogue' dimming is really nothing more than a variant of 'PWM'. However, when it comes to LEDs, physiology says that human eyes tend to judge brightness of pulses by their peak intensity, and people like eric who have 'done the experiment' (in a classroom or wherever) seem to have largely confirmed that - which has to make one wonder how good PWM is at achieving human-perceived LED dimming! If/when I have some time, I might try some experiments myself!

Kind Regards, John
 
PWM dimming does work for LEDs.
It's obviously bound to work to some extent. It just seems to me, on the basis of what I'm being told, that a given change in mark-space ratio is likely to have much less effect of 'perceived dimming' with an LED than with an incandescent lamp. That, in turn, suggests that effective PWM dimming of LEDs might require such low mark-space ratios that flickering could become an issue.

However, perhaps what I am being told is not true!

Kind Regards, John
 
PWM dimming does work for LEDs.

It does but to achieve the appearance of a dimmed lamp requires more than simple PWM If the average current is 1/2 the rated current ( 50:50 mark:space ratio) then the LED will appear to most people to be almost full brightness. A few people will see it less than full brightness due to their eyes having a different retention time.

In 2015 I spent a lot of time programming a PWM LED driver to make the LED simulate a flickering candle. These were for 30 hand held lanterns at my daughter's wedding. The light source had to be LED due to constraints on the size of battery that would fit into the handle ( a PP3 ) It took a PIC12F1822 processor with a few hundred lines of program code to get a good simulation. All the fixed lanterns used incandescent lamps which did respond well to PWM "flickering"and required far less coding on the processors.

With a quick search, I came across this document that discusses the changes and reasons.

That to me is an explanation of the shortcomings of the LEDs they produced befire 2008 and the effect these short comings have on the light produced.
 

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
Back
Top