Why aren't many / most LED light bulbs dimmable?

Page 4 of 7  
On Mon, 27 Dec 2010 13:36:14 -0600, " snipped-for-privacy@att.bizzzzzzzzzzzz"

This is a Fluke 8060. I doubt that is a big deal and it was constant between the LED with and without the pot. I suppose there is still some drop tho. I have a hand full of Hi Intensity LEDs from those TV wonder lights that I am going to play with tonight. I made a light bar out of some wood scrap that matches my cabinet and I am going to see what happens. I do believe, if you are dimming a LED array, low voltage may be your friend, both from an application standpoint and a safety/UL listing standpoint. Things are pretty lenient on the load side of a listed class 2 power supply. I figure I will start out with a ballast resistor selected to apply about 15ma "all in" and dim from there. From my experience with the flashlight I think a 25 ohm pot will do a pretty good job and I have one.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 27 Dec 2010 15:40:13 -0500, snipped-for-privacy@aol.com wrote:

Looking at the spec (for the 8062, looks to be the same as the 8060A), the burden voltage on the 2A range (next down is 200mA and you said 211mA) is .9V (.3V on the 200mA range). That's at FS, but I'd want to measure it to see how much of that is resistive and how much is fixed. That'll certainly throw a monkey wrench into your readings.

DC is your friend. PWM it. ;-)

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I meant several series strings -in parallel-.
curiously,some free Harbor Freight 9 LED flashlights I have have all 9 LED's in parallel,and no current limiting resistor,depending instead on the internal resistance of the 3 AAA cells.
--
Jim Yanik
jyanik
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That's a current-sharing nightmare waiting to happen. I suppose the LEDs are all from the same batch, so at least in theory, it works. ...well enough for cheap Chinese junk, anyway.
Thinking about it a little, the temperature coefficients are in the right direction so at least the thing isn't going to run away.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yes, you are correct, except that the LEDs have to have a "threshold"[*] voltage to light at all. If the dimmer is triggered when the AC (sine wave) is too low the LEDs don't light. The range of adjustment will be very small. [*]as others have pointed out, this isn't an on/off thing but is highly nonlinear

Yes, this is a very expensive thing to do, compared to a *cheap* Triac dimmer.

You'd have to make a DC source, which won't be cheap because of the sine-wave input. The source will have to store energy for the cycle.

No, they adjust the (phase) angle of a triac firing. This controls the power put into a resistive load just fine but doesn't work for a highly non-linear load like a (long) string of diodes.

Right. But you don't have DC to chop. ;-) Making the DC isn't all that cheap (or efficient).

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 12/24/2010 12:50 PM, snipped-for-privacy@att.bizzzzzzzzzzzz wrote:

Hey Don,
What do you know about what circuitry is in the commercial LED lamps and dimming compatibility.
For those who don't know, Don Klipstein knows more about lighting than anyone I know of:
http://members.misty.com/don/ledx.html
We'll see if he is around and interested.
Jeff

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Sadly, I have yet to look inside any retail-available LED lights over 2 watts, nor most 2 watts and under. I don't remember too well what the packages that I looked at so far say.
Best I can say is, look at the fine print on the packages for compatibility with dimmers.
The Philips ones at Home Depot *may* be a good bet. However, I did little more than glance at their photometric and color specifications after getting "sticker shock".
So far, I am seeing only here-and-there applications where LED "bulbs" appear to me more appropriate than CFLs or incandescents, mostly for light output near or less than that of a 25 watt incandescent and with a lot of "on time" per day.
One more thing: Most white LED units claiming 100,000 hour life expectancy, especially cheaper and non-major brand ones, significantly fade in 4,000 to 50,000 hours. I generally recommend green or blue LEDs for nightlights. Any LED "security lighting" that must be at least basically white should be by or have LEDs made by *major* brands of "lighting grade" LEDs, such as Philips/Philips-Lumileds, Cree, Nichia, Osram/Sylvania, Citizen/Cecol, and the like. Also, the usual "bullet shape" low power LEDs are unlikely to get past 10,000 hours before significantly fading if they are white unless they are greatly underpowered. I know of one LED nightlight "bulb" that does make use of underpowering to achieve true long life from cheap white low power LEDs. That is the Feit 3-LED candelabra base one.
One more thing: For outdoor or basement nightlighting or security lighting, I strongly recommend that any white lights (LED or otherwise) be of cooler color (more bluish, higher color temperature). This is because night vision is significant in such dimmer lighting environments, even if colors and sharp outlines are visible. A spectrum richer in mid-green to mid-blue favors greater illumination in this case.
--
- Don Klipstein ( snipped-for-privacy@misty.com)

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 26 Dec 2010 21:31:57 +0000 (UTC), snipped-for-privacy@manx.misty.com (Don Klipstein) wrote:

For indoor, basement, indoor security, and night-lights, I'd think you'd want more of a red so you don't spoil your night vision. ...or maybe a white photo-flash and cover *your* eyes, while the no-good gets blinded. ;-)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I've tried all sorts of things for seeing around with little light. My experience says to make use of night vision. A cool white LED can illuminate a room to extent that I can walk around and see everything, using a couple to a few percent as much light as if I used red light.
--
- Don Klipstein ( snipped-for-privacy@misty.com)

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 26 Dec 2010 23:56:01 +0000 (UTC), snipped-for-privacy@manx.misty.com (Don Klipstein) wrote:

That's interesting and a bit counterintuitive. I can see fine around the bedroom, at night, with only the backlight of my XM radio but it's quite bright. I guess it's not enough to trigger the iris but still make use of the higher sensitivity wavelengths. OTOH, for astronomical viewing (and submarines ;) one uses red lights.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Oh yes, I do remember my stretch of time when I was into astronomy.
Red lights were used to see things other than stars, such as star maps, so as to see in high resolution (from photopic vision) with light that does not overload and reduce sensitivity of scotopic vision.
I would think the requirements of nightlights are usually different. I don't see the need to be able to read a newspaper - only to recognize it, to be able to read the name of the newspaper. There is also the fact that I don't mind having my night vision attenuated a bit by using a light that makes use of it for this purpose. I have some green and blue LEDs that can illuminate a largish living room that well to me with maybe .1 milliamp (and full dark adaptation), though I would only count on low current performance good enough to do that with .25 milliamp.
--
- Don Klipstein ( snipped-for-privacy@misty.com)

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 27 Dec 2010 16:54:10 +0000 (UTC), snipped-for-privacy@manx.misty.com (Don Klipstein) wrote:

I still don't want to lose "night sight" when I stumble from one room into the next, at night. The light doesn't alter my Braille ability, though. ;-)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

<SNIP to here as part of editing for space that I did here>

I'm thinking that illuminating a largish living room with one of my favorite green or blue LEDs at .1-.25 mA will be low enough on blasting my night vision for me to still have a majority of it, probably around/over 75% of it.
Then again, I can illuminate all rooms and the basement of a McMansion that brightly with 50 milliwatts for the whole house. :) (Not that I get a good ROI for doing so, in comparison to getting commercially available LED nightlights using ~100 times as much power and producing a few times more light.)
--
- Don Klipstein ( snipped-for-privacy@misty.com)

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 12/26/2010 4:31 PM, Don Klipstein wrote:

Thanks for joining in. I hope it is more joy than aggravation. I take it that the failure is with the phosphors and not with the junction generating the UV? Interesting as most of us had been thinking of LEDs as being forever. I have noticed that many of the new LED traffic lights have sections out. I don't know whether that is a circuitry break or whether an LED actually failed. In the environment they are in I would think connection failure from thermal cycling. Either internal or external.
Jeff
I know of one LED nightlight "bulb" that does make

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

<Lots of editing for space>

White LEDs fade mainly, almost entirely, from the phosphor degrading.
BTW, the usual white LEDs have phosphor over blue LED chips, not UV ones.
I am also noticing many LED traffic lights with some LEDs out. That appears to me to be, as you say, broken connections. I don't know where they're breaking. One thing I notice is that affected LEDs are disproportionally at the edges of the traffic lights around where I live. This makes me suspect stress concentrated at the edge of a PCB that the LEDs are on, so I wonder how well the PCBs are fitted to what they are mounted to.
--
- Don Klipstein ( snipped-for-privacy@misty.com)

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Dec 24, 11:50am, " snipped-for-privacy@att.bizzzzzzzzzzzz"

Note: http://joby.com/store/gorillatorch/switchback
Joby makes several models of quality dimmable LED lights, but as you said they are not cheap. The one in the link will dim thru a range of 5 - 130 lumens, mostly linear and without flicker. I have one and it works great. I have no idea of the circuitry they use to dim the LED and I'm not going to take it apart to find out. This response is just to let the doubters know that the technology to dim LED's is real and available.
Red
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Sure dimming LEDs is possible, and actually not all that hard if you start with DC (the unit you linked is battery powered). Doing it from the AC line, cheaply and efficiently, is more challenging. It's easy to do sloppily, but then there is no gain over an incandescent bulb.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 24 Dec 2010 19:12:39 -0600, " snipped-for-privacy@att.bizzzzzzzzzzzz"

I still do not get how you arrive at that conclusion. A string of LEDS will draw 15 - 20MA at full brightness and if you increase the size of the current limiting resistor the current will drop from there in a very linear manner.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sat, 25 Dec 2010 11:53:35 -0500, snipped-for-privacy@aol.com wrote:

Try it. You'll find that you are *very* wrong. LEDs are *not* in any way linear. You'll also find that the efficiency goes down as you lower the brightness (the resistor takes more of the line voltage).
If you use a current source it works, linearly, but is no more efficient (think of the current source as a non-linear variable resistor).
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sat, 25 Dec 2010 20:04:00 -0600, " snipped-for-privacy@att.bizzzzzzzzzzzz"

Why do you think the voltage across the resistor changes? You have a certain voltage dropped across each junction and the resistor takes the rest. The resistor is a current regulator not a voltage regulator.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Site Timeline

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.