Lightpix FlashQ Q20 II output

[fotopan]

Could any of the Lightpix Q20 II owners share actual power measurement of his flash? My flash meter for ISO 100 and 5 meters shows F stop 2.8, which translates to GN 14 - instead of 20 shown in the flash specification. Is this normal or is my flash faulty?

 

[RalphLambrecht]

Could any of the Lightpix Q20 II owners share actual power measurement of his flash? My flash meter for ISO 100 and 5 meters shows F stop 2.8, which translates to GN 14 - instead of 20 shown in the flash specification. Is this normal or is my flash faulty?

Maybe faulty math? Have you considered distance squared or measured at a distance of 1 meter?

 

[koraks]

My flash meter for ISO 100 and 5 meters shows F stop 2.8, which translates to GN 14 - instead of 20

It's one stop difference compared to what it's apparently supposed to be. Not all that much.
Looking at this flash unit, it's a tiny little strobe. I wouldn't expect miracles from it, power-wise. It looks like a very richly featured unit with lots of ways to use it; I think that's its main selling point. Not so much raw power.

maybe faulty math? have you considered distance squared?

Huh?
Guide number = f-number × distance
He measures 2.8 at 5 meters. That's GN 14.
Specs say GN20; 20/5 = f/4. One stop difference. I'd call it "manufacturer's sales-enhancing optimism".

 

[fotopan]

Maybe faulty math? Have you considered distance squared or measured at a distance of 1 meter?

I believe the math is OK as koraks said. At 1m the F stop is 13.

 

[fotopan]

It's one stop difference compared to what it's apparently supposed to be. Not all that much.
Looking at this flash unit, it's a tiny little strobe. I wouldn't expect miracles from it, power-wise. It looks like a very richly featured unit with lots of ways to use it; I think that's its main selling point. Not so much raw power.


Huh?
Guide number = f-number × distance
He measures 2.8 at 5 meters. That's GN 14.
Specs say GN20; 20/5 = f/4. One stop difference. I'd call it "manufacturer's sales-enhancing optimism".

Right, I don't expect miracles from unit this tiny I would only like to know if the real GN like 14 is a standard for this flash. If it's just mine that's weaker than the specification, I'd rather exchange it for a better copy

 

[koraks]

If it's just mine that's weaker than the specification, I'd rather exchange it for a better copy

Devices like these tend to be quite consistent. I wouldn't bother trying to get it swapped as there will be no expected improvement.

Mind you, the difference might not even be one stop. Between meter calibration and rounding issues, it's quite possible the real guide number is somewhere between 14 and 20 (although it might also be a little less than 14, as your 1-meter measurement suggests).

Anyway, I understand your question and hopefully someone will come along with the same unit who is also in a position to do some measurements on it to put your mind at ease.

 

[Chan Tran]

I don't have a Q20 II to test but I test many flash units and found none meets the published GN. They are always less from 1/3 to 1 full stop.

 

[wiltw]

Could any of the Lightpix Q20 II owners share actual power measurement of his flash? My flash meter for ISO 100 and 5 meters shows F stop 2.8, which translates to GN 14 - instead of 20 shown in the flash specification. Is this normal or is my flash faulty?

Almost 20 years ago, several of us tested our flash units with flashmeters, and virtually universally found claimed GN of even big name brands (Canon, Metz, Sunpak) seldom matched the measured GN as determined by flashmeter. We published our results on POTN, which no longer exists from which to extract past information

 

[fotopan]

This is basically what I found, too - none of my flashes, whether Pentax, Godox or Metz, match the published GN, and the differences are sometimes quite large. However, these are mostly older flashes and some have seen a lot of use, so I'm not particularly surprised. Still, it would be nice to know if the Q20 II I own is within a norm for this flash or not.