Here's a real breakhrough on LED lighting technology

[Old and In the Way]

http://www2.electronicproducts.com/PageSearch.aspx?FName=hlrc03_oct2009.html

Working from 110 to 220-Vac power sources, the Acriche 4 ac LED has an efficacy (luminous efficiency) of 75 lm/W, surpassing competing dc LEDs. Further, the devices will cost 10% to 20% less than dc devices.

Unlike dc devices which require complex driver circuitry, the ac LEDs need only a simple, inexpensive diode bridge (full-wave rectifier). The A4 uses 50 Vrms per package, and 110 to 220-Vac operation can be achieved by connecting multiple devices in any manner needed. (Less than $1 ea/ prod qty — available this quarter.)


LED bulb technology today requires an electronic module to convert and reduce the AC power to DC power...this changes everything.

[MineralMan]

1. Uh...with a bridge rectifier, this one converts AC to DC too.

Unfiltered DC, perhaps, but DC nevertheless. It's still cheaper, but DC all the samce.

[joshcryer]

2. Will this lower operating lifetime?

[MineralMan]

4. I don't know. If it's just a simple four-diode bridge,

the resulting current will have fluctuations at a rate of 120 Hz. They're not all that large, but they're there. Whether that will lower the useful life of the LEDs, I don't know.

I'm just objecting to their assertion that other systems convert AC to DC, when there's does the same. I haven't examined the output of a traditional LED driver, but I imagine it's pretty well filtered. It could be that there's a fatigue factor for the LEDs when unfiltered DC drives them, but that's beyond my pay scale.

Here's a graph showing unrectified, half-wave rectified, and 4-diode bridge rectified output at the bottom.




And here's a filtered full-wave bridge rectified output waveform:



Notice the sharply-reduced fluctuations in the bottom waveform. This is done with a simple capacitor to smooth the voltage variations. Classic old electronics stuff.

[OKIsItJustMe]

5. Most of the LED's I've known in my life flicker (largely) imperceptably

Take an old LED calculator and wave it in front of your face. Watch the after-images. Or, eat potatochips while looking at a chain of "Christmas" LED's.

It doesn't seem to affect their lifespan…

[MineralMan]

6. That's true. You're probably right.

[TheMadMonk]

7. That's because the display segments are not all driven simultaneously.

It is a process called multiplexing, which allows one set of wires to supply/comtrol multiple devices. One digit of the display is turned on at a time, then the next, the next and so on 50, 60 or hundreds of times per second. Try reading a digital clock (or watch TV) through a fan.

[OKIsItJustMe]

8. I suppose the fan would work too

I've liked the “potato chip method” since I discovered it as a child.

Cogito ergo spud — I think, therefore I yam.

[TreasonousBastard]

3. The CRI of 85 still sucks for lighting, but...

at least it's better than a lot of the crap in the past.

It is designed for higher voltages, so the reduction from 120 all the way down to to 2 isn't needed, reducing complexity, and I'm guessing the higher voltage is the main reason for the higher light output. The bridge still is necessary, but you always could run LEDs with just a bridge.

When is someone going to come up with an LED lamp with a CRI over 90? How hard can that be?

[hunter]

9. Last time I looked I decided it was a tangled mess of patent issues.

It may be better now. The blue LEDs with the inadequate phosphors have turned a lot of people away from LED lighting. These bluish lights remind me of old mercury street lighting. I remember when the town I grew up in went from cheerful incandescent street lighting to the most hideous mercury lighting you can imagine, transforming the entire city into a zomby nightmare. When the city went to orange high pressure sodium lighting it was a vast improvement, but still not as cheerful or as inviting as the expensive inefficient incandescent lighting was.

For LEDs these guys are expensive, but they usually have the latest and greatest:

http://www.environmentallights.com

Anybody have any other suggestions?

[TreasonousBastard]

10. First one I looked at had a CRI of 70, about...

what a warm white fluorescent has. That, the price, and the need for a 24VDC power supply kills if for the undercabinet kitchen light I need.

The desk lamp didn't have the CRI mentioned, but it's 5000K and they say it's "natural" so it's prabably a very nice light. A little pricey, but nice.

Right now, I can find fluorescent tubes and, occasionally, CFLs with CRIs over 90 and 3000K, 5000K, and 7000K temps. The prices aren't much more than the standard lamps and even though they don't have the efficiency of LEDs, they're plenty efficient. Heaviest lighting use I have is the kitchen ceiling light-- twin 40W tubes with under 5% less output than a standard cool white tube. I'd like to replace that, but there's nothing else around that would do the job. My table and work lamps with CFLs running 6-24 watts don't run enough to ever justify LED replacement at anything close to their current cost.