# LED Bulbs



## Chris S (Sep 30, 2008)

Anybody have a any luck with LED lighting in the home?

I bought some LED bulbs- put one in a 6" recessed light-  very white light not too bad
Put 2 in 5" recessed lights - too little light
Put  a bulb in a bedside lamp- OK for reading
Put one in the porch light wall fixture not too bad.
These were 3-8 watts of light replacing 55-65 watt bulbs, so great savings, but no wheres near the Lumens 
Anybody find something they really like?

Chris


----------



## Valhalla (Sep 30, 2008)

I prefer to use CFL. They are not prefect, but you do get used to them quickly. After a while, you don't know you have them.


----------



## SteveT (Sep 30, 2008)

The past couple of years we've used strings of LED's for outdoor Christmas lighting. They look great and the electricity savings are substantial (estimate $30 or $40 each year).


----------



## Jerry_NJ (Sep 30, 2008)

The only LED for 115vac house bulb sockets I've found are at Walmart and are 1.5 watt (almost free electric power-wise) and claim to be 40W equivalent. They are not to my eye and the light is a "scary" white light.  Still I like them for some applications, maybe for an outside "standing light" for security, not for reading.  The problem I've had is the first two I purchased at Walmart failed within the first 100 hours of use. Walmart did, of course, refund my purchase price.  A couple of days ago after finding the Walmart display fully stocked again I purchased another, for a light in the basement in a dark corner that I can leave on most of the time.  It has been working fine so far....still waiting to see if there is an early failure.  

I look forward to more, seems the first poster may have some, some at a hight light output, say 4 watts for 100 watt equivalent output.  It would be nice too if the ligh color could be a little warmer.


----------



## begreen (Sep 30, 2008)

I've tried a couple and so far am not impressed. I don't like the cold, bluish light, even for outdoor Christmas lights. For indoor use, the lumen output of the unit I got is weak, more night light level than reading level. I'd love to see this technology take off, but the light output needs to be higher, color temp warmer and the cost needs to come down a magnitude.


----------



## jebatty (Sep 30, 2008)

They're coming, and color will get better. Local bldg supply (Menards) has LED nightlights for about $2. Great advantage is that they take very little power, are very cool running, and last almost forever. An especially good use is for the nightlight on the refrig - don't need any heat here. We only use the night lights when we have guests who can't find their way around the house in the dark as they search for the biffy. CFL's everyplace else.


----------



## Corey (Sep 30, 2008)

I guess it really depends on what color you like.  I searched high and low for CFL's that accurately reproduce a good incandescent bulb "white" without being too red or too blue.  I finally found a bulb I liked, only trouble it it comes on at about 40% brightness and takes a couple minutes to warm up!

Same goes for LED's.  Everyone has their own taste from blue-white to pure white down to warm white.  I picked up a pack of 100 of these off ebay:

http://cgi.ebay.com/100-PC-0-5-Watt...3098859QQcmdZViewItem?_trksid=p3286.m20.l1116

Have plans to make up a couple of units possibly to install around the wood stove and or around the TV.  I can usually be found around one or the other for the cold winter nights and usually have the lights dimmed pretty low for nice ambiance.  I would say the color rendition in the ebay photo is pretty true to what you actually get...a nice warm white light.  A single LED seems to put out about the same light as a candle.  (Which may have additional use around Halloween!) Each 'LED' package is actually 5 discreet LED's in series for a 100mW current draw.


----------



## jebatty (Sep 30, 2008)

If you buy ready-made LED lamps, they typically consist of the LED's, a bridge rectifier, and a resistor to limit current. They also can be powered by a single diode rectifier and a resistor. You can make these up yourself. You need to know the rated current, which varies by the LED chosen. Then use Ohms Law to calculate the resistor value.


----------



## Jerry_NJ (Sep 30, 2008)

I assume an LED is forward biases and "drops" between 0.7 and 1.0 vdc when emitting light.  So, if one takes 1 vdc and looks at the suggestion that at least one fixture has 5 LED in series, that accounts for approximately 5 volts.  Or too small to bother with, thus pick a resister that limits the RMS (or Peak?) value of the house ac, to the desired current of the LED, perhaps 100ma.  That being the case R= 120/0.1 = 1.2K would be about right, and the wattage would have to be greater 0.1 x 120 = 12 watts, this doesn't sound good, as the LED I have on hand claims to be 1.5 watts, must be the diodes use a lot less than 100ma, maybe only 10ma, that would bring the power down to 1.2 watts, about right, so the current must be around 12ma.  Indeed we can computer the rms current as 1.5watt/120v = 12.5ma.

Interesting.


----------



## granpajohn (Sep 30, 2008)

A traditional traffic light, (red, yellow, green), uses a clear incandesent bulb at each color. I think they are 120w and they come in bulk at a dirt cheap price. However, they do burn out in a very annoying way. So, traffic engineers are slowly replacing these systems with LED lights which cost over $100 each. Worth it if they don't burn out and cause crashes. 

They have found that they do, in fact, fail at about a 70% rate. They don't care, because the manufacturer offers free replacement. Hopefully this will improve.

The LED systems use less power to the tune of about 10w. Varies from 8-13w depending on the color. This gives them the big advantage: They can be run on battery power, (from the cabinet), during power outages. These batteries last 4-6 hours. Best of all, since outages often last much longer than that, it is easy to send a man out to an intersection to replaced the batteries with a fresh charged set. (2-4 gel cels IIRC). Hence, the savings is in labor cost.

Took time to get these things to work, because it was difficult to get the green panel. They looked rather blue at first.

So anyway, it is very important to have a long life warranty, like Jerry_NJ did, because otherwise it can be a lot of money spent/wasted.

Oh, and, I don't think I want my family room to look like it's lit with a traffic light.


----------



## jebatty (Sep 30, 2008)

This looks like good info on LED's:

http://www.kpsec.freeuk.com/components/led.htm


----------



## DiscoInferno (Sep 30, 2008)

Jerry_NJ said:
			
		

> I assume an LED is forward biases and "drops" between 0.7 and 1.0 vdc when emitting light.  So, if one takes 1 vdc and looks at the suggestion that at least one fixture has 5 LED in series, that accounts for approximately 5 volts.  Or too small to bother with, thus pick a resister that limits the RMS (or Peak?) value of the house ac, to the desired current of the LED, perhaps 100ma.  That being the case R= 120/0.1 = 1.2K would be about right, and the wattage would have to be greater 0.1 x 120 = 12 watts, this doesn't sound good, as the LED I have on hand claims to be 1.5 watts, must be the diodes use a lot less than 100ma, maybe only 10ma, that would bring the power down to 1.2 watts, about right, so the current must be around 12ma.  Indeed we can computer the rms current as 1.5watt/120v = 12.5ma.
> 
> Interesting.



If you use a resistor in series with a few LEDs and power it directly with 120V as you suggest, then the vast majority of the power is going into the resistor and not the LED.  Using your numbers, there's 5V across the 5 LEDs and 115V across the resistor.  Since they all have the same current, this means that 115/120=96% of the power is lost as heat.  For any semblance of efficiency you would need a step-down transformer or DC-DC converter before the LEDs.


----------



## jebatty (Sep 30, 2008)

I suspect this is why you find white LED bulbs with multiple LEDs, like 18. White LED's take 4 volts x 18 = 72 volts. If a single diode is used, half wave rectifier, approximately 1/2 of line voltage is passed to the LED's, or 60 volts. No resistor needed.


----------



## Jerry_NJ (Sep 30, 2008)

Good reference jebatty, thanks a keeper.  I had no idea an LED drops 2 volts plus.  I see you mention 4 volts for white.  The 1.5 watt, so called 40 watt light output has something like the 18 LEDs you note.  That goes a long way to increasing efficiency, but they are so efficient in any case that we can afford to wast a lot of the power in a limiting resistor to keep the package light and cheap.  

Interesting too to read so many fail early, that's been my experience.  I'm now on my third one trying to get one that lasts more than a week.  They are suppose to las 30,000 hours, and Walmart will take them back for a refund for 90 days.


----------



## RedRanger (Sep 30, 2008)

We have achieved a much longer life from our CFL`s after remembering to leave them on for a minimum of 20 minutes before turning them off.  Big difference.!  Turning them on and off frequently seems to kill-em fairly quickly.  Traffic lights are mentioned in this thread, so can I assume the same rule doesn`t apply to LED`S?


----------



## jebatty (Oct 1, 2008)

I don't think I've ever had a single LED fail, as opposed to a multiple LED lamp, of which I have none. LED's will fail quickly if they are exposed to higher than rated voltage. Perhaps voltage  surges or spikes are killing them? It might be better practice to under-voltage them and provide surge/spike protection, both of which would add to the cost. Penny wise vs pound foolish?

I can't relate any of my CFL bulb failure to turning on and off frequently. I think sometimes I'm more conscious of failure of a bulb that is turned on and off frequently than I am of a bulb that is left on for longer periods of time. In all events, over the past several years the overall failure rate has been low, which I am guessing to be maybe one bulb out of 10. At the same time, we have several CFL's that have lasted more than 10 years, get lots of use, and still are going strong. I think it balances out.


----------



## jebatty (Oct 1, 2008)

An idea for easy LED use on your electrical equipment - add a single rectifier diode and resistor and use as a pilot light. I added two to my generator, one to each side of the 240 volt line. I was having trouble with a plug connection of the generator itself that was making one line intermittent. Got very easy confirmation that both lines were hot.

I'm also going to be adding LED pilot lights to the circ pumps on my boiler. There is enough space in the wiring box to do this, and I will drill a hole in the case and just use friction to hold the LED to the case. Some circ pumps now come with an LED pilot light.

I was thinking about using an LED pilot to quickly let me know if my new 4000 watt-equivalent LED searchlight was on. LOL


----------



## Jerry_NJ (Oct 1, 2008)

I don't have any general complaint about the life of CFL bulbs, which we have used extensively for more than 10 years.  I do know that the lamps I have on timers, on at dusk, off around midnight, have the most hours on them, and the seem to just keep going.  I know some of these have been in this on for about 10 hours a day for years.  Yet, we do have failures, and as sonnyibc says it may be due to short on/off cycles.  

I can see too how the LED 120vac fixtures I've used have such high rates of failure:  1) so many bulbs in series, just like cheap Xmas tree lights, any one fails, string goes out and 2) I had the LED bulbs in a frequently switched location (head of basement stairs).


----------



## Jerry_NJ (Oct 1, 2008)

I've used simple "neon" lights with a resistor, no diode needed, for pilot lights.  I have one on my electric timer for the hot water heater, it has been working for years, maybe 15 years, and still going strong.  The long life is due in part to a high resistance resistor, picked by trial-and-error, so the light isn't very bright, but still easy to see.  Yes, I like pilot lights too, on the same subject my almost new HWH (well about 6 years old) has pilot lights on the upper and lower heating elements.  I do look at time from time-to-time to see if one is on.


----------



## Redox (Oct 2, 2008)

Jim, you don't really need an additional diode; the LED already is a diode and will work on AC or DC.  

Chris


----------



## dvellone (Oct 2, 2008)

I've searched extensively for leds for quality indoor lighting and haven't come up with much. I've found some that work well for task and reading lighting - pleasing color and ample light- but I don't think that the quality area lighting is here yet. A bit more rise in fossil fuel and bit more drop in the market and those leds may just be around the corner.


----------



## Jerry_NJ (Oct 2, 2008)

Redox, good point and works as long as the reverse breakdown voltage is high enough.  Seems if a number of LEDs are in series the reverse breakdown voltages add, so no single diode has to take the full "reverse" voltage.  This make the cheapo circuit simply a resistor of the right value...albeit this isn't the most efficient, but so what, the LEDs need so little current that loss in the resistor isn't large either.

The big surprise to me is that the forward voltage drop is so high, stated at 4 volts in this thread for white LEDs.

Is there any data (empirical) about how long the next most efficient, the CFL, it has to leave on before turning off if the cycle isn't to have a detrimental effect on the blub life?  sonnyibc mentioned 20 minutes or something like that.  If true, I'd guess they need to be on long enough to come up to full brightness.  Just a guess.


----------



## DiscoInferno (Oct 2, 2008)

What I've read says that the current crop of white LED-based lights are still less efficient than current CFLs.  LEDs are usually more directional than CFLs, which means if you compare based on peak brightness rather than total light power LEDs fare better.

I think that the large forward drop in white LEDs is because they are internally composed of 2-4 different-color LEDs in series to approximate white.
Edit: It looks like phosphor-coating blue LEDs is the more common method used for white LEDs, and 3.5-4V is about right for blue LEDs.


----------



## jebatty (Oct 2, 2008)

> Jim, you don’t really need an additional diode; the LED already is a diode and will work on AC or DC.



Should have known this. I've only used LED's in low voltage situations, so the rectifier diode plus resistor is what I have done. Could also use a transformer to deal with reverse voltage breakdown, but that kind of defeats the small size advantage of the LED in a circuit.

What about, though, the result being only using 1/2 the power being supplied? Is this a PF question? Wouldn't a bridge rectifier produce approximately twice the efficiency?


----------



## jebatty (Oct 2, 2008)

> Jim, you don’t really need an additional diode; the LED already is a diode and will work on AC or DC.



Should have known this. I've only used LED's in low voltage situations, so the rectifier diode plus resistor is what I have done. Could also use a transformer to deal with reverse voltage breakdown, but that kind of defeats the small size advantage of the LED in a circuit.

What about, though, the result being only using 1/2 the power being supplied? Is this a PF question? Wouldn't a bridge rectifier produce approximately twice the efficiency?

[sorry about the double post]


----------



## Jerry_NJ (Oct 2, 2008)

I have a problem with the statement:  "white LED-based lights are still less efficient than current CFLs", given what I know about LEDs.  Talking about equivalent light to tungsten bulbs (the standard) a 40W CFL runs in the 10 watt consumption range, while the LED is 1.5 watts.  Now I agree the CFL 40W puts out more light to my eye than does the 40W LED, but not 6 times more light.  

Also, a more complex power supply:  step-down voltage and full wave bridge rectifier would increase the efficiency of the LED light on an A/C circuit.  But, this complex power supply will have some of its own losses, will be bulky (by comparison) and will add serious cost.

Given the low cost of a full-wave bridge and a resistor, an LED setup that uses enough LED in series to approach 100 volts to light-up full should be very efficient, albeit a fixed brightness.  This would be about 25 LEDs which is still not very bright in my experience.  

I'm not sure if more LEDs adds more spread of light, or more intensity, or both.  This suggests for brighter LED fixtures two banks of 25 LEDs, in this example, which has two banks in parallel each has its own rectifier and resistor thereby eliminating the parallel "problem".  The two banks are in effect each connected to the A/C source.


----------



## DiscoInferno (Oct 2, 2008)

Jerry_NJ said:
			
		

> I have a problem with the statement:  "white LED-based lights are still less efficient than current CFLs", given what I know about LEDs.  Talking about equivalent light to tungsten bulbs (the standard) a 40W CFL runs in the 10 watt consumption range, while the LED is 1.5 watts.  Now I agree the CFL 40W puts out more light to my eye than does the 40W LED, but not 6 times more light.



From the DOE:
http://www.netl.doe.gov/ssl/PDFs/LED-FAQ.pdf
"The best white LEDs are similar in
efficiency to CFLs, but most of the
white LEDs currently available in
consumer products are only marginally
more efficient than incandescent lamps.
Lumens per watt (lpw) is the measure
of how efficiently the light source is
converting electricity into usable light.
The best white LEDs available today
can produce about 45-50 lpw. For
comparison, incandescent lamps typically
produce 12-15 lpw; CFLs produce at
least 50 lpw."

I agree this will not be the case for long, but CFLs have a significant head-start in terms of commercialization.


----------



## Jerry_NJ (Oct 2, 2008)

Hum, thanks, I am surprised at the nubmers for LEDs vs CFL.

Perception, perception.... is reality in many ways.  Regardless of what the DOE says, never mind they are an (incompetent?) government agency, I see and have applications for LED lights in 120vac fixtures that save a high percentage of electrical energy as measured against CFL.  One is as I stated in an earlier post, and application in the basement that is dark day and night and has meters and other devices view several times a day.  The 1.5watt LED ligth is sufficient light, the lowest wattage CFL I have seen is 9 watts.  Does it produce more light, maybe, but at 7 times as much energy.  And, as has been discussed, the CFL life is reduced if turned on/off frequently.  With a 1.5 watt LED there's not reason to turn it off anyway....not sure its life is impacted by on/off cycles.

In cold weather I also have some "standing" lights I leave on outside.  I'd do it in warm weather too, but the bugs/insects are too much.  In those application I will also try the 1.5 watt LED and see how it works.  As my goal is to have enough light to see is something is going on in the near area, I think it will work fine, and at the reduced power consumption as compared to a low output CFL.


----------



## DiscoInferno (Oct 2, 2008)

I assume that the 1.5W LED light is more of a directional (spotlight-type) light?  Is it sufficient light everywhere, or just directly in front of the light?  CFLs are pretty omnidirectional unless equipped with a reflector, so if you compare based on peak brightness (candelas) rather than total light power (lumens) the directional LED light will win.  In applications that call for small spot lighting, this suggests using LEDs.  When trying to light a whole room, this suggests CFLs (for now).  What are the specs on the LED light?

I hunted around the internet out of curiosity, and I didn't find any commercial LED lights that did significantly better than the numbers given in the DOE document.  A typical one I found - 2.3W producing about 100 lumens, which corresponds roughly to a 15-20W incandescent light bulb.  What I didn't find is much in the way of 60-75-100W incandescent replacements.

As an aside, government career scientists are generally quite competent.  Management, especially at the high levels where the positions are political appointments, not so much.


----------



## Jerry_NJ (Oct 2, 2008)

The LED I'm testing, purchased at Walmart, is boldly listed on the package:  Replaces 40 Watt, Use only 1.5 Watt.  90% More efficient than incadescent and halogen bulbs, 30,000 hour life.  Mercury Free (good), and somewhat less eye catching "decor/accent" which suggests not for use as general lighting.  My observation is the light is not a spot light, but appears to have a more central/downward brightness, and it is less light to my eye than one sees with a 40 Watt incandescent, or a 40 Watt replacement (9 Watt or so) CFL.  The package does not give a lumens number as do the packages on incandescent (required by law I think).  Again, to my eye this 1.5 Watt (I have not yet measured the power input) LED puts out less light than a 40 Watt incadescent, but clearly more than a 20 Watt....I must have one of these around and I give it the "eye test" to see how much light the 20 Watt puts out.

It may be like with flashlights.  If I want to see over a distance of 200 feet or more outside I'll take my 14.4vdc lantern outside.  I don't have any "big" LED flashlights, but I can say one of my 3 AAA cell 4 LED flashlights is a real wimp by comparison, but inside where I don't know that long distance light the 4 LED flashlight does just fine, and runs a lot longer on 3 AAA cells than does the drill battery driven hand lantern.  One thing is clear to me, LEDs give usable light a far lower power consumption than any other electric lighting device I have experience with.


----------



## jebatty (Oct 2, 2008)

If anyone with a "40 watt" or so equivalent LED lamp has a Kill-a-watt meter, please test amps, watts and PF for the LED and an "watt equivalent" CFL. That should make an apples to apples comparison with real data. I have the Kill-a-watt meter but no LED with which to do a comparison.


----------



## Jerry_NJ (Oct 3, 2008)

Well I have both an A/C volt meter, and an A/C clamp on Amp meter with good low current sensitivity (multi-loops).  So I can easily measure volt-amps and the Watts used is less-than or equal-to VA.  In the subject case I expect to measure an A/C current less than 10 ma.  I'll "publish", after I watch the Palin/Biden discussion.  Maybe not until tomorrow.


----------



## jebatty (Oct 3, 2008)

otherpower.com reports the following info on lighting efficiency. White LED's according to this article are about as efficient as incandescent. T8's look the best way to go for shear efficiency.

    * 32 watt T8 fluorescent--85 to 95 lumens/watt
    * standard F40T12 cool white fluorescent--60-65 lumens/watt
    * compact fluorescents--low 30's to low 60's lumens per watt, usually 48-60
    * UPDATE 12-2006 -- The newest white LEDs shipping from manufacturers in 2006 are approaching the efficiency of compact fluorescents, into the 50-60 lumens/watt range. At this time, however, there are no RE lighting products that use these new LEDs, and they remain extremely expensive. Manufacturer's research labs are also reporting new white LEDs that approach the 80+ lumens/watt of T8 fluorescents. However, these products are not shipping yet.
    * T3 tubular halogen--20 lumens/watt
    * white LED--15-19 lumens/watt
    * standard 100 watt incandescent--17 lumens/watt
    * incandescent night light bulb (7w)--6 lumens/watt
    * incandescent flashlight bulbs--dismal, less than 6 lumens/watt

http://otherpower.com/otherpower_lighting.html


----------



## Jerry_NJ (Oct 3, 2008)

Thanks "jebatty" this is the kind of data, even if a surprise to me, that I've been looking for, apparently not hard enough. I had posted questions about LED applications for residential lighting on another forum, may have been either electronic or electric, and I didn't get much.   I'm not sure why different fluorescent "geometries"  have different efficiencies.  I'll check, but I believe the T8 is a circular bulb, and it has significantly higher efficiency.  I had moved almost totally to CFL, but it is possible to use the round bulbs in my unfinished basement and garage applications just as easily as the CFL.


I'll do a cut-and-past into my Palm notes your good effort above, along with the url reference.

Still, I see some high efficiency uses for LEDs in my case. That's not to say I couldn't make equal or better use of a CFL if there was one using only 2 watts or less.  The lowest one I have is a 40 Watt equivalent and 9 W.  

More on the eyeball test:  in my basement at night I see the 1.5 Watt LED a bit less light than a 25 Watt Incandescent, and a 9 Watt (40 Watt equivalent) has a bit more than the 25 Watt, but not a true 40 Watt replacement.  So, I still see applications for the 1.5 Watt LED fixture I got from Walmart, some very inexpensive high duty (on) cycle applications.


----------



## jebatty (Oct 3, 2008)

I think T8's are pretty much standard, including the 4' shop style lights.


----------



## billb3 (Oct 3, 2008)

A fair indicator of the lack of efficiency of some of the "super white" LEDs is the whopping size of the heat sink needed.


----------



## Jerry_NJ (Oct 4, 2008)

Some home empirical results.  The main problem with the LED measurements is they are too low for the electric power equipment test equipment I have.  The lowest range on my clamp on amp meter is 6 amps.  I used a loop of 4 turns which made the lowest range 1.5 amps full scale, thus I could see 100 ma, but not 10 ma.

I tested as a reference a 25 Watt Incandescent bulb (should be about 200 ma) to note the meter deflection. I then used a 9 Watt CFL specified at 140 ma (which suggests a large power factor if the real power is only 9 Watts) and noted the meter deflection compared to the 25 Watt Incandescent.   In any case when I plugged in the 1.5 Watt LED (specified at 30 ma) I couldn't see a measurable deflection on the meter, suggesting it was less than the 30 ma.  But, even if it were 30 ma the maximum power that could be consumed (all real power) is 3.6 Watts.  So what do I conclude:  I conclude the LEDs in the current crop of Walmart sold LED fixtures have a higher efficiency than do CFL.  The 1.5 Watt LED fixture puts light over an area, not a spot light, that is at least half that of a 9 Watt CFL, or said another why 6 of these LEDs would swamp the light put out by a 9 Watt consumed CFL while using approximately the same real power.


----------



## jebatty (Oct 4, 2008)

CFL's approximately use 1/4 to 1/5 the watts of an incandescent lamp for the same lumens of output. An incandescent is a pure resistance load with a PF of 1. Using my Kill-a-watt meter, I tested several CFLs, and the PF ranged between a low of .44 to a high of .7, making their effective advantage over incandescent of power used (VA) for lumen of output ranging between a little less than 2 to about 3. The newer CFLs had much higher PF than the older CFLs. All the CFLs I tested had electronic ballasts.

I believe most homes are charged for their electricity based on watts, not PF (contrary to many businesses). So cost-wise, CFLs do have their advertised advantage.


----------



## Jerry_NJ (Oct 4, 2008)

Interesting, a power factor as low as 0.44 on some CFL would cause a simple amp reading to be much higher than expected watts/volts, which I think I saw in my measurement.  Not sure what the case is for LED fixtures, but I can't imagine there is any significant reactive power in them, i.e., power factor should be 1.  In any case, I was happy to have difficulty even detecting the A/C current into my 40 Watt (claimed 1.5 Watt consumed) LED fixture.  Thus I'm willing to estimate that the fixture is consuming the 1.5 Watts, not some higher number due to losses not included in the advertisement/claim.  Again, the LED fixture does have 30 ma printed on the bulb base, suggesting it can using either twice the 1.5 Watts or there and a significant "imaginary" part (power-factor < 1).


----------



## jebatty (Oct 4, 2008)

I think I'm correct in stating that an LED will "waste" at least 1/2 the power delivered from an AC circuit. And probably a little more if a rectifier diode is used along with a resistor/and or a capacitor.

I have a 120v AC LED night light, 3 white LED's, uses a bridge rectifier with a resistor. Put in on the Kill-a-watt: 1 watt, 7 VA, PF of .22. But very interesting is that readings stay the same whether or not the LED is "on." It is consuming power all the time, not just when it is "on."


----------



## Jerry_NJ (Oct 4, 2008)

Thanks, not sure anyone else is reading, a PF of only 0.22, due to the capacitor it seems.  I'm surprised the design went to the trouble to add a capacitor, across the output of the bridge rectifier to act as a (HF) filter, i.e., to make the rectified ac more dc-like. 

I'm not sure what you mean about the LED being "on" verses "off".  That is in my case the on/off switch is in the ac feed line, so the current/power is zero whenever off.  If the fixture has its own switch and that switch is on the LED side of the "power supply", then the capacitor could sit as a load even when the LED is "off".  The good news is this is reactive power, i.e., imaginary, and you will not be billed by the power company for that borrowing of power.  In fact, power companies like capacitive loads, they help cancel the local inductive (motors) nature of most power loads.  

The only LED fixture I have is sealed and everything fits into a clearly visible internal plastic-like structure that could easily hole a full-wave bridge and capacitor, even a large value capacitor as is needed to deal with low frequencyies, 120 pps on the output of the bridge.  

I'm a EE, albeit it a manager for the last 30 years, so the subject is interesting to me and testing my long term memory  :red:


----------



## billb3 (Oct 4, 2008)

jebatty said:
			
		

> I think I'm correct in stating that an LED will "waste" at least 1/2 the power delivered from an AC circuit. And probably a little more if a rectifier diode is used along with a resistor/and or a capacitor.
> 
> I have a 120v AC LED night light, 3 white LED's, uses a bridge rectifier with a resistor. Put in on the Kill-a-watt: 1 watt, 7 VA, PF of .22. But very interesting is that readings stay the same whether or not the LED is "on." It is consuming power all the time, not just when it is "on."



If you open the AC circuit, there's no AC power to "consume".


----------



## Redox (Oct 4, 2008)

The only thing it is wasting is time.    

The LED is only going to conduct in the forward direction.  On the negative half cycle, it actually goes dark and is really flashing 60 times a second and will appear dimmer to the human eye (that whole persistance of vision thing).  The full wave bridge is converting the negative cycle to a positive and this makes it look brighter with the same current.  It's still flashing 120 times a second, but the dark phase is very short.  

As for the power factor, I would expect it to be 1 as the major part of the load is the dropping resistor, but I have no way of testing this.  The problem is that the Kill-a-watt is probably not going to be very accurate at such a low load.  I have compared the K-a-w with a Fluke power analyzer and it appears to be very accurate with loads of several hundred watts, but at the single digit level, I can't tell.  I have plugged a few CFLs into it and they do seem to have a poor power factor, but this doesn't matter with a typical residential meter.

I have only seen one LED lamp with a medium base that will replace a standard light bulb.  Anyone know of any?  I think they would be great in the refrigerator and maybe the bathroom.  CFL's don't seem to last in frequent on-off applications for me.

Chris


----------



## Jerry_NJ (Oct 4, 2008)

redox, the LED fixture I keep referring to has a medium (standard light bulb) base and I purchased it at Walmart.  In fact this it the third purchase at Walmart, the other two went back for a refund when they failed in a few days.  Both had been in a basement stairway overhead and were switched on/off 10-20 times per day.  The one I'm now using, testing, is in a dark corner of the basement, and I turn it on/off once a day.  So far so good.

As for the flashing due to the rectified sinusoidal ac waveform, that's what the subject capacitor is all about, could sit behind the bridge, but before the "power supply" output current limiting resistor.  This capacitor will reduce the LED "flashing".  It also adds some reactance to the load, thus a power factor less than 1.  

I think I'll make a 10 turn "amplifier" for my clamp on amp meter so that my low range will be 0.6 amps rather than the provided 6 amps.   This will allow me to measure ac currents as low as 100 ma with some accuracy.  Of course this will not address the need to measure true power.  I do have a dual trace oscilloscope, so I should be able to measure the phase angle between the voltage and current.


----------



## DiscoInferno (Oct 5, 2008)

You're making me want to get out my Fluke Scopemeter and start playing with circuits again.  It's probably been 10 years since I've done much on the hardware side where I wasn't mostly looking over someones shoulder.  I'm a theory/math/matlab type EE nowadays.

Re: LED flashing - Some LEDs are actually capable of higher total light output if fed a high-current, low duty-cycle pulsed waveform rather than lower-current DC.  Looks like that mainly applies to low-power LEDs, however, and not the white LEDs we're talking about.  Basically they are more efficient at higher currents than the max steady-state current, but the duty cycle has to be reduced to keep them from burning out at the high current.


----------



## Redox (Oct 5, 2008)

I'll have to check out that fixture, but I have an aversion to going in a Wal-Mart.  

Why not just insert an ammeter in the circuit to see what is going on?  It's going to be a lot more accurate at the current levels we are talking about than a clamp on.  Meter accuracy depends on the range of the instrument and I suspect that your 6 amp analog Amprobe (really a 200 amp meter with a low range, IIRC) isn't going to be all that accurate when you can barely get the meter to deflect.

We have a few strings of LED X-mas lights that I find irritating because of the flashing.  I suspect that they have no external rectifier and are just allowing the AC to be rectified by the LED.  We also have some LED night lights that don't flicker bad enough for me to notice.  I doubt they bother with a capacitor, but a bridge might be possible.  

I was under the impression that LED life was determined by the peak current and solid state just doesn't tolerate overcurrent well.  The current, intensity and lifespan are going to be determined by the resistor you choose.  I recall a SMT pick and place machine where I used to work that had a vision system with LEDs that only lasted about 20 hours due to the high current.  You can push any LED closer to the edge, but will sacrifice their lifespan.  I'm getting kinda used to not changing the CFLs as often and look forward to a lamp that lasts for 50000 hours.  Now if we could just make it bright and white...

My new TV set has an LED light engine.  No problem with brightness there!

Chris


----------



## Jerry_NJ (Oct 5, 2008)

redox, yes on the amp meter sensitivity, that's why I mention a ten loop "amplifier".  I think the "adding" of the magnetic flux is accurate, i.e., it will increase the sensitivity of the clamp on by a factor of 10.  As for a meter in series, well then I have to break one leg open, and that then introduces the resistance of the series inserted meter, but that may not be a problem as the circuit has high impedance/resistance.  I'll have to look to see what I have ... yes my Radio Shack Micronta digital multi meter, must be ten years old, does have an AC ma capability, so I do have equipment to directly measure low current AC.  I may get around to that tonight, and think it may be easier to "insert" the meter than to make the ten loop magnetic amplifier.


----------



## Jerry_NJ (Oct 7, 2008)

Spotted today in a Harbor Freight sale paper (mailed to my home, boy is that old fashioned?) an A/C power meter, for only $30.   It is hard to see and has very little information in the "flier" but it does state limits of 120 vac and 15 amp ac, reads in Kilowatt hours and measures power factor.  It has a digital display.  The ad doesn't say anything about the ranges over which it can be used, but with a digital meter it may be capable of displaying small values, e.g., watt-hours or smaller.  Here I assume the display in in KWH per hour.   I may buy it.


----------



## Redox (Oct 8, 2008)

It it this one?

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93519

I think that is the older model and it loses the info if the power goes out, but it seems to be accurate with a couple hundred watts to measure.  I think a meter that measures 1800 watts is going to have a problem with a fraction of a watt.  Remember that meter accuracy is measured as a percentage of full scale reading and just because it's digital doesn't make it any more accurate.

Chris


----------



## Jerry_NJ (Oct 8, 2008)

Thanks Chris, I tried to get some specifics on sensitivity, and found some better close-ups of the meter than HF gives.  In fact "smarthome.com" offers the same meter for a few dollars less.  

I understand the 0.2% accuracy applies to full scale, but it specs some impressive accuracy.  That's why I was trying to find out if it is possible to change the "scale".  It appears it from the front panel that there are no range settings.  It does show one button as KWH/Hour, so maybe that means it can be used to time something or to show KWH (per hour, I assume).  

I may purchase, it looks like nice "toy" for everything but LED level units.


----------



## jebatty (Oct 8, 2008)

The Kill A Watt is what I have, gave me some very surprising info on electrical usage of some common household items -- especially when they are "off." Learned that the dehumidifier was the biggest electrical hog of all (and it was an Energy Star appliance!); that a 1950's era frig was an energy miser; that having the volume higher on the sound system made virtually no difference in electrical usage.

The Kill A Watt was instrumental in us reducing our electrical usage by 30% in achievement of one of our major conservation goals in 2008.


----------



## Jerry_NJ (Oct 8, 2008)

Hi Jim, thanks for sharing you experience.  

While the unit is undoubtedly most useful in determining power hogs, one question I'll ask is how small a reading can you take. As the subject of this thread turned to measuring the real power of a LED light fixture, that is my current interest.  As you may have read, I am able to read volt/amp but not power or power factor, and indeed small loads like 2 watts (or volt/amps) is difficult to measure with my on had equipment.

Will the Kill A Watt read as low as a watt or two?


----------



## jebatty (Oct 8, 2008)

I am not able to check accuracy on the very low consumption items. When I put a CFL rated at 14 watts, I get a 14 watt reading; same thing with a light bulb at 100 watts. I don't have anything with lower wattage.


----------



## Jerry_NJ (Oct 8, 2008)

Jim,

Thanks, that's helpful.  If it reads 14 watts for the CFL, I assume it'll measure 1 watt as well.  I may buy and see.


----------



## Chris S (Feb 23, 2010)

For anybody still following this, I installed an LED replacement in a 6" recessed fixture today-  from Cree.  awesome light- as good as a 60w lamp for .....12w
cost about $ 100


----------



## Seasoned Oak (Feb 23, 2010)

Sams club has the best selection of LED recessed bulbs About $7 each,also the candelight small base LED bulbs.  THe Xmas lights are Great, but the home lighting selection is still somewhat spotty


----------



## velvetfoot (Feb 23, 2010)

Geez, I read most of the thread and then realized it was from 2008.
Around here in Albany, NY, there are led billboards.
Can't say if they're more efficient than the lit up versions, but they are a distraction.


----------



## btuser (Feb 25, 2010)

I bought the LED Christmas lights.  Awesome, but they give off so little heat when it snows they don't melt and you have to get them uncovered.  7watts vs 70.  You can string like a million of them together.


----------



## velvetfoot (Feb 25, 2010)

I have read that there is a similar problem with traffic lights and snow/ice not melting.


----------

