Cold Ohm's Testing of PAR 64 Lamps


Senior Team Emeritus
Premium Member
Back in 2012, there was a conversation about cold ohm’s testing of lamps. Meaning testing the lamp’s filament by way of Ohm’s of resistance when the lamp is not running - just off/storage/in cold mode.

I was so hopeful in testing this theory for a problem, my staff and I tested well over a hundred new 1Kw PAR 64 lamps of many brands, but mostly the newest Generic China brand of lamps. Meter everything, see what we get..... starting to see a trend of most lamps reading between 1.25 and 1.05 Ohm’s, let’s segregate every lamp not within that range. This in addition to another important detail pointed out some other day for design issue with the newer PAR 64 lamps.

Back about than there was also a national Lighting Technicians Certification test of some sort. Believe there was a question on it about a HPL lamp ohm's reading.. Was it really just E/I=R? Volts devided by Amps = Ohms of resistance, or was it a different formula more useful for lamps that one cannot test anyway unless operating.... and at that point the Amps is easier to measure in... 8.333+ equals 1Kw.

silicsound Oct 3, 2012
“If you try and use ohms law to find the resistance of each lamp wattage, you will find that the resistance will be around 20 times less in practice since the lamp is cold. As far as the condition goes, resistance should increase with age.”

Per Osram “Tungsten Halogen Low Votage Lamps Photo Optics” c.2000, (the manual on lamps - and should have a link somewhere on the CB website.) Yes, used lamps will have a decimal of in the Hundred’s in factor for properly operating halogen lamps for Ohm’s reading. For the most part a properly operating halogen cycle will by ETC Sensor dimmer rack with buffering for current and warming adjustment if properly adjusted, age of lamp will have very little noticeable Ohm’s difference in a lamp.. Found no real differences in testing some used lamps also.

In addition to Friday’s tested lamps, I just Ohm’s metered out well over a hundred 1Kw PAR 64 lamps of multiple brands today - mostly the discontinued name brands GE and Osram, and a few of the Keller Williams holdover GE lamps - post GE discontinuing the lamp & while in Mexico filament change before China. This was including some used lamps.

All were tested with a Extech #EX530 meter. My readings given probes instead of clamp jaws (Fluke clamp jaws were tried without any better results.) Were widely ranging in all brands of lamp, but the (Cold Norm) seemed to be mostly in the 1.27 - 0.99 range with a lot of outliers. Ohm’s readings were at times in the 2.6 Ohm range, at times much larger, and at times the meter could not range to a set reading. I believe this much to contact with the probe and or the weld of the lamp’s ferrule (pins) to the GX-16d prongs.

It can be safely said that even though there is differences in beam spread, there is no ohm’s cold difference between a VNSP and WFL 1Kw PAR 64 lamp - a question I wanted to confirm.

A sampling of today’s testing of new lamps:
1.00, 0.96, 0.98, 1.15, 1.01, 1.18.

Generic Keller Williams (Mexico) w. GE markings - FFN:
3.16, 1.34, 1.68, 0.99, 1.28, 1.09, 1.77, 1.13, 1.24, 1.37, 2.52, 1.84, 1.01, 1.41, 1.09, 1.02, 1.07, 1.39.

1.13, 1.19, 0.98, 0.97, 1.24, 2.12, 0.99, 1.21, 1.95, 1.07, 1.31, 1.06, 1.37, 1.07, 1.04, 1.00, 1.01, 1.24, 1.20, 1.02, 1.09, 2.64, 1.00, 1.00, 1.06, 1.13, 1.02, 1.47, 2.25, 1.02.

Osram - FFS:
12.30, 2.33, 1.39, 1.20, 2.39, Bad, 2.24, 1.17, 1.18, 1.53, 26.17

1.28, 1.10, 2.52, 1.62, 1.22, 1.06, 1.07, 1.02, 1.00, 1.04, 1.07, 0.99 1.15, 1.02, 1.00, 1.04, 1.07, 0.99, 1.15, 1.07, Bad, 1.68, 1.00 (used), 1.76, 1.31, 1.13, 1.63, 1.09, 1.11, 1.10

Generic Keller Williams (China?) Without GE Markings and same otherwise as Generic China Brand. Vertical instead of horizontal filament noted for this lamp also:
1.20, 1.21, 1.22, 1.27, 1.24, 1.20. Ohms’ Resistance per Cold lamp.

The rest of the (China) lamps tested I don’t have my notes at home on, but I would say 90% of them in the Generic China only brand - without the Keller Williams branding (on the outer case) are within a range of 1.25-1.05 Ohms resistance. The last 10% are similar in out of norm, Really odd resistance, or over 1.30 range for cold resistance. Could almost say, in cold Ohm’s metering... the new China Generic PAR 64 lamps are on average while cool testing more in the above normal range than the percentage of GE or Osram lamps.

Did a quick check of some used 750w Philips #7981P and many brands of used 500w BTL lamps in cold Ohm’s testing:

1.21, 1.26, 1.60, 1.86, 1.56, 1.85, 1.36, 1.40, 1.23, 1.69
Only 5 of 8 BTL lamps tested would provide a stable reading (as found on some or high Ohm’s PAR 64 lamps amongst brands at times.)
2.01, 2.02, 1.90, 1.94, 1.94 ohms.

So... cold lamp ohm’s testing of lamps in general does not have any relevance other than perhaps if you get a good reading... a 750w/115v #6981P lamp perhaps is in the 1.5 range of ohms resistance average? Yet the 500w/120v BTL lamp is in the 1.23 Ohm range. In other words, cold Ohm’s testing it would seem is no real measurement of a cold lamp’s actual working resistance to current flow by way of wattage. Or even much so far without running the out-liers in testing if an indication of quick failure.

Amperage testing of an operating lamp shows some promiss. This especially with outlier lamps. Testing will require new lamp sockets to all fixtures to test in adding to the physical testing. Amongst other details.
1Kw PAR 64 lamps of today's Generic China version.... something in study. The lamp captule change on the fixtures I see, TBA for research and complience specifications.
As with the monofoils in resistance and heating up, and various welds. A quious thing in requesting a testing of six sample lamps happened today. The GE FFN lamp sample failed quickly. If I remember right, it was 1.47 ohm's resistance and was a FFN lamp.
If on an ETC dimmer, they are both buffered to electronically compensate for in-rush current, and pre-warmed in a voltage to pre-warm the filament and halogen cycle. Granted pre-warming as opposed to testing or perhaps the tour going full on... possiblily negating it.

Took a break from the PAR 64 concept today in getting a reply from a friend that the Ohms law is the measurememt cited above in lighting technition's test. So unless the samples of various cold test PAR 64 lamps sent out to test show more results... Deveations in the norm for cold Ohms reading on a lamp is a good way of testing a lamp for working, but after that... not much useful.
Still have a few outlier lamps to test in verifying that there is no use for this. Gonna power up the worst for measurement in seeing if they blow sooner than others.
At this point, there is no indication that China Generic lamps have any worse failure problems than other lamps for static - not touring install.
China lamps in testing all brands - including the GE from stock which blew on the six example lamp bar burning in... is inclusive in no other lamps blew up, and all GE/Osram/Mexico/China/China/China tested 8.3 Amps. and at short focus, no noticable differences. Hung on a testing bar so no other testing was done.
Given these lamps with an axial instead of horizontal filament structure for the lamp capule will also effect optics, in addition to in say a 1:40 lamp ratio the lead in support wire was noticably closer to the front lens than on others... I had to stop buying the lamps.
I also requested the lamp spec. and data page along with some ANSI and other compliences governing accepted failure rate compliance from the China company - origionally known as Keller Williams when in Mexico as a brand literally supplying once GE making them went down... had the GE boxes and cases, and were making the same GE lamp.
In searching my stock lamps, was evidence that at some point in Keller Williams while making the lamps in Mexico to the specific GE standards, started making these lamp capsules axial instead of horizontal. Than either still the brand, or sold off it to China as name brand... not acceptable for rigging gear for brand... perhaps now as lamp maker.

I do not consider this brand my main supplier has been suppliying me with lamps for, to currently be an ANSI lamp he has supplied me with. I suspect that these changes to the lamp that they helped me get a very needed supplier for given the Corning/GE sell off problem and panic was best placed effort in helping me with a good supplier. Problematic change over, but decent for a time in quality type a thing until the above.
On the other hand, my main supplier for most all lamps is now quiet on replying on this question. For actual working to spec. PAR lamps, I had to switch suppliers given my main lamp supplier is researching a new supplier that will be more expensive, but better.... no word other than that. Suspect they no more than me want to deal with this years old problem. But one has to at least commicate. He is working on it... and in the mean time I switched to a different supplier which lists an actual brand on the lamp I am yet to research,. but at least is within ANSI spec. for the lamp.

I don't openly list suppliers of lamps - the company I work for is also a supplier of most all lamps, in not doing business (sales) in advice policy I have and CB has supported.. (Unless you are the only supplier with such a thing... you can list yourself amongst other sources for a lamp.) My listing of lamp suppliers going back to the beginning of the website... but getting in troublele at one point from an unscrupulous supplier in listing all but his company and my own company. That unscrupulous supplier attemped to black mail me into only buying his lamps... or he would tell my boss's that I was advising lamp sellers other than him and specificly my own company.... Granted... we were a "Dealer of their lamps" and they were not selling lamps to the public - but were.

Long story short. If the PAR 64 lamps you purchase have indications that their is a filament support stucture for a PAR 64 lamp close to the reflector, or that lamp capsule is on the same axis of the lamp... you should probleably return it. If "China" is the only indication on the lamp box... one might return it. These I think are not ANSI compliant PAR 64 FFN-FFS lamp and might be problematic in lasting to expected lamp life. Send them back. Explosions of little glass fragments falling can also be a liability problem of concern.
Last edited:
Would it be possible to get the specification sheet for the China PAR 64 lamps?

Amongst questions I have are the filament structure in use, compliance with ANSI lamp standards given the filament/lamp capsule is mounted vertically in the lamp capsule instead of horizontally?

Does this effect beam spread? Does this explain the Amperage reading below = CBCP the same if the beam spread changes? Are there photo optic beam spread changes now?

Does the capsule support arm now in use, in proximity to the lens, especially in about 4% of lamps noticeably closer to the lens potentially overheat the lens?

Given it's a new lamp capsule orientation, is it using the same cc-8 filament, or perhaps as per single ended lamps a cc-16 for a FEL or c-13D for EGT lamps? Is it's capsule support, and filament support structure strong enough for touring purposes?

Per Osram "Tungsten Halogen Low Voltage Lamps Photo Optics" c.2000, p.32 Does this manufacturer comply with AQL standards / DIN 40080 on lamp quality/failure & testing standards?

...Mark from Osram was thinking Amglo might be able to make these lamps if big enough want from a customer. Amglo is a very quality supplier for lamps in my own thoughts of them agreeing. Too bad his AluPAR machinery got sold off or that would be an easy switch + lighter lamps which I'm told is important to the tour in already maxing out weight of truss so doing LED heat sinked PAR's if powerful enought would as with fixtures not work. I was thinking Eiko still might have the ability to start making them again.
Past emails on the subject about expectations or hopes.
The science is there for the Aluma PAR lamp, as with the science for the HPR lamps in improving known problems or upgrades.
Way back when... I invested into GE HIR lamps. That went nowhere. Example:
FCM Ushio #1000489 T-3/4 CL, Quartz 1Kw R-7s Mol 4.11/16"/3,200°K/28,000L/400h
G.E. #13895 T-3, HIR, 4CL, Quartz IR Film 650w R-7s MOL 4.11/16"/3,275°K/25,200L/400h

As a quick comparison. I asked, but did not get into the AlumiPAR concept because our tours were very happy with the normal 1Kw PAR 64 lamp. This was before the GE/Osram/Philips/Ushio/Eiko normal 1Kw PAR 64 lamp lamp was discontinued.
A concept that LED heat sinks are adding too much weight, or too expensive... Any support in cobining ideas on lamp science for a new (granted filament lamp) that might also qualify for energy standards savings, and as per a fix, such a new PAR 64 lamp invention?

Users who are viewing this thread