LED bulb question
 

Two different LED bulb models by the same manufacturer. Packaging says:

bulb1: 800 lumens, 2700K, 150 mA @ 120V, 8.5 watts

bulb2: 800 lumens, 2700K, 120 mA @ 120V, 10 watts

Can someone explain what's going on here?

Re: LED bulb question
 

The two bulbs might operate at different power factors (PF).

Power factor is defined as the ratio of power (Watts) consumed to apparent power (Volt-Amperes) drawn. Resistors and old-fashioned incandescent light bulbs operate at unity power factor, because all the current they draw follows the applied voltage instantaneously; no lag, no distortion. Inductive loads such as transformers and AC motors operate at less than unity power factor because their current draw lags the applied voltage. Electronic loads, such as the AC to DC converter circuits inside LED light bulbs, operate at less than unity power factor because their current draw is distorted relative to the line voltage. But, not all AC to DC converter circuits are created equal; some distort more than others, so some operate at lower power factor.

The first bulb in your example operates at PF = 8.5 / (120 x 0.15) = 0.47

The second bulb operates at PF = 10 / (120 x 0.12) = 0.69

It would be worthwhile to test these two bulbs using an inexpensive meter such at the Kil-A-Watt, to see how well actual performance tracks their markings.

Re: LED bulb question
 

Interesting my first thought was different efficiency emitters for the different models could account for the same light output with different consumption. but the math on the wattage doesn't add up.

The other question is one a dimmable and the other not?

I had an interesting experience recently when I installed a non-dimmable LED bulb in a fixture that was connected to a lighted switch. Turned on the switch and everything worked fine. Then I turned off the switch and periodically the bulb would flash on for a very short period. Scratching my head and then looking at the lighted switch the light in the switch would flicker corresponding to the bulb flashing. I later put a dimmable bulb in that fixture and the flashing stopped.

In retrospect I concluded that the slight voltage leak through the switch's illumination allowed the capacitor in the non-dimmable bulb to charge to the point where current would flow through the LED. It would then drain the capacitor, the light would go off, the capacitor charge again and the cycle repeat.

So a dimmable bulb would have higher consumption at the same light output due to the added control circuitry's power consumption. But that of course does not explain why the math doesn't calculate out.

Re: LED bulb question
 

I was wondering about that.

Bulb2 is dimmable; bulb1 is not.

Interesting you should mention that. It's on my list of useful tools I should look into. Do you have one of that model?

Re: LED bulb question
 

Yes, and you are welcome to borrow it. PM to arrange a meeting time.

I happened to have two Cree LED bulbs marked 2700K 800 Lumens 9.5W 120V 60 Hz 79 mA on hand. From my household 120V, both draw about 8 Watt, 70 mA, and both measure PF = 0.88 using my Kil-A-Watt.

Their markings indicate ~unity power factor: 9.5W / (120V x 79mA). Small print also says they are UL Listed and suitable for damp locations. Another marking 2213 suggests they were manufactured in Week 22 (late May/early June) of 2013.

What brand are your LED bulbs?

Re: LED bulb question
 

Walmart "Great Value".

They were selling them for 82 cents a piece so I picked up a dozen.

Re: LED bulb question
 

Hey Richard,

I picked up a Kill-A-Watt yesterday.

I tested it with a standard* 60 watt incandescent bulb in an outlet whose voltage reads 123.6 V. The Kill-A_Watt says it's drawing 33.9 watts / 33.9 VA (PF=1) and 0.27 A. I had not expected that.

Would you please test a standard* 60 watt incandescent bulb with your meter?



* i.e. not "long life"

Re: LED bulb question
 

Will do that. Right now I am on the road coming back from New Hampshire, so it may be late Saturday before I can post again.

Re: LED bulb question
 

I just tested a 750/1500 watt dual heat resistive space heater with the Kill-A-Watt. The readings made sense. Power Factor 1.00 (as expected), and watts approximately 765 (on low) and 1443 (on high).

When I get a chance, I'm going to test a larger sample of incandescent light bulbs of various brands and power ratings.

Re: LED bulb question
 

I just tested three GE Reveal incandescent light bulbs with my Kil-A-Watt.

The 29W bulb measured 28 Watts, 0.23 Ampere, 1.0 power factor.

The 60W bulb measured 60 Watts, 0.5 Ampere, 1.0 power factor.

The 75W bulb measured 76 Watts, 0.63 Ampere, 1.0 power factor.

As expected.

Re: LED bulb question
 

I don't have any GE Reveal here, but I tested a bunch of GE Soft White incandescents and they all measured roughly half their wattage rating (with PF=1.00).

Do you have any GE Soft White bulbs? If so, could I ask you to test them?

Re: LED bulb question
 

What about the LED bulbs that started this discussion, have you tested them? Inquiring minds want to know.

I do have to wonder if there is a problem with Ether's Kill-a-watt in accurately measuring at the lower end of the range. I was under the impression that the difference between the standard, soft white and reveal bulbs was purely the coating on the inside of the glass and not due to a different filament. So in theory they should all match their wattage ratings within the expected tolerance of a high volume mass produced item at low price point.

How about plugging a power strip in with that heater on low and a lamp with the bulb and comparing the results with and without the bulb on?

Re: LED bulb question
 

Thanks for the excellent suggestion.

34.2W bulb only (60 watt soft white incandescent)

755W heater only

811W heater plus bulb

811-755 = 56W

Power Factor was 1.00 for all readings above.

Spec accuracy is listed as 0.2%

I think I may have a defective unit.

Re: LED bulb question
 

I was thinking about the bulb's tolerances, but the Kill-a-watt's tolerance is an important part of the equation as well.

Is there anything in the documentation that would indicate the tolerance is different at different parts of the range? If it is just a stated .2% then I'd have to agree that you seem to have a defective unit based on Richard's results with his. +/- 1 Watt seems to be as good as would be expected on a product like an incandescent bulb.

Re: LED bulb question
 

Have you tried measuring the bulb resistance with a DVM?

Re: LED bulb question
 

The max watts spec for the unit is 1800W.

So even if 0.2% means 0.2% of 1800, the unit is still way out of spec.

Re: LED bulb question
 

The resistance of the bulb changes substantially as the filament gets white hot.

I don't have a DVM that uses 120 volts to measure resistance.

.

Re: LED bulb question
 

... and the inexpensive DVMs I have access to don't support measuring AC current with 120V applied.

Re: LED bulb question
 

I just called the tech support number and the friendly fellow who answered wasn't able to shed any light on the situation.

.

Re: LED bulb question
 

Richard, If you are still following this thread, could you please take a peek at the label on the back of your Kill-A-Watt and compare it to this and flag any differences for me? Note especially the red arrows.

I'm wondering if your unit is an improved version.

I bought mine at Menard's, and they appeared to have been hanging on the rack for quite some time (packaging covered in fine dust). Also, the printing on the cardboard label inside the thermal-welded plastic packaging is copyright 2011.

Re: LED bulb question
 

Data point: My Kill-a-watt is wildly inaccurate at very low (< 10W) power levels: Some of my light bulbs don't even register any reading. (This is based on measurements more than a year ago. I should try to repeat them now).

Re: LED bulb question
 

Mine is older than yours. Model 4400, yours is Model 4400.01

Mine is also marked Conforms to UL STD. UL 3111-1, yours is 61010-1

Mine is marked Voltage: 125VAC Power: 1875VA, yours is 120VAC, 1800W

Re: LED bulb question
 

Is your DVM sensitive enough to measure the resistance of a power cord? If so, you could measure the resistance (without 120V) and the voltage drop (with 120V through it and the lamp, before the power cord heats notably) to calculate the current flow. It will not tell you anything about the relative phase of current and voltage through the lamp, however.

Re: LED bulb question
 

I'm wondering how long ago you bought yours and and how much it cost. I paid $20 at Menard's.

Here's my working hypothesis: to get the price down and appeal to a larger market, the newer model (4400.01) uses cheaper components with larger tolerances.


Don, would you please compare the label on the back of your unit to this and note any differences?

Also, could you try your unit with a 60W incandescent bulb and tell us what the Watt readout says?

Re: LED bulb question
 

There is always the amp function of your DVM. :]

The cold resistance gives you a reference to tell if things are really strange. You can also make some assumptions and do a little math and see if a simple physics model matches reality. Tungsten (assuming your filament is really tungsten) has a resistance temperature Cef of 4.5E-3 at 20C. (Assuming it is linear all the way to white hot is a big assumption at least for me.) Using 120 VAC for the rated voltage 2500K as the bulb temp and a little excel math I get about 22 ohm cold. Am I close? Of course with a 240ish ohm hot resistance the cold resistance doesn't tell you that much without a tested model.

Re: LED bulb question
 

None of my 8 (inexpensive) various models of digital or analog VMs measure AC amps in the desired range.

The cold resistance of 60W soft white incandescent bulb measures approx 18 ohms.

Don, if you're still reading this thread: does the label on the back of your Kill-A-Watt say model P4400 (like Richard's) or P4400.01 (like mine) ?