Can we talk about dimming?... PWM-style or not?

[awardblvr]

Does this thread already exist? If so, please reply with pointer.

Fabulous insights by the Lutron guys.... This PDF is a WHOLE COURSE on dimming LED's in homes and commercial settings:

It shows the current state that the big guys are dependent on dimming by special hecka-expensive powers supplies, magnetic and Electronic Low Voltage (ELV) dimmers. What a mess!!! And these ALL seem ultimately to just get varying current to the LED's to provide dimming, NOT PWM. WTH???

There are many manufacturers who appear to have dimming drivers which DO use PWM and are far less expensive. Like EZD-4C8A with EZD-1C-WM . This is FAR more economic than the Lutron or other big-players. The primary reason given in the presentation is that "US homes are not wired for DC". BUT, running DC wires through walls is easy... Even with a little sheetrock patching! (Yes, of course use Plenum-grade good jacketed wire with sufficient gauge... bla bla bla)

So, what gives here? Why do these manufacturers shy away from simple solutions?

Then the follow-up is: Why is it a bad idea to take track lighting, use the tracks for 12V (or 24v) DC, PWM-dimmed and fixtures which can accommodate, say dimmable MR16's? and use these? Why are very few seeming to aim products at that implementation?

(So, the context of all this is that I need to re-do the lighting in a lecture/presentation class room by using LED strip lighting around the edge of the 9' white-ceiling room to provide dimmable ambient light with LED strip plights pointed at the ceiling on 45degree angled aluminum. And then to put track-lighting over the students conference-tables to provide flexible lighting focused to illuminate the class participants notes, but allow overall room darkening during presentations.) Any suggestions appreciated.


Thanks All!

 

[ShineOnYouCrazyDiamond]

I'm sure similar discussions have occurred, but the way you raise it brings up the topic in a different way.

I think that we've just seen the beginning of LED lighting. The current designs are mostly way to retrofit LEDs into the current fixtures that are present in everyone's home. It's the only way to get market penetration at this time. The future will definitely bring a new round of LED lighting that is designed to be LED from it's inception. Light bars around the ceiling - maybe a whole light bar under cabinet counters. I think over the next 10 years we'll see some pretty cool stuff.

In terms of the PWM, the cheapest solution is not really the best. Using a half-wave rectifier is a very cheap was to get DC but you will get a 60 Hz flicker - which is very visible. If you use a full-wave rectifier then you end up with a 120Hz flicker - which is less visible, but irritating when you are moving your head around. Especially irritating in the kitchen if it keeps bouncing off a moving reflective knife blade.

The best way to get a smooth PWM dimming module is likely to do a very clean AC to DC conversion and then generate the PWM at a frequency in the 2,000+ Hz range so it is not visible under any type of movement.

As far as what is best, I guess it's a matter of personal preference. With PWM you don't get the tint shift from the LED as you dim it down so your lighting will stay a consistent color. With pure current control the LEDs will tend to shift warmer as you dim them - which could have a nice aesthetic effect similar to how an incan bulbs warms as you dim it.

 

[adnj]

I see the issue of running DC wires a problem because code does not allow for running DC alongside AC wiring. It may seem like a simple task to run the DC cable but many existing buildings (think concrete walls and floors) require conduit for wire routing. Sheathed cable is not allowed unless it is armored.