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The U18 on my JoshK sphere reads 680 lumen.
The U16’s read 635 lumen.

Basically my JoshK sphere reads a couple percent less than my TA Tube.

You might need to subtract a little more for reflector and lens loss, plus a little for driver loss. I was looking at Koef3’s V5 xpl chart and you can see that at 2.3A there is no way the U18 can achieve 1090 lumen. Impossible. It’s still a good little light, though. I don’t think the average person really cares if it’s 700 or 1100 lumen, it’s still plenty bright.

These new TA Tubes are reading noticably lower than other lumen tubes like the ones built by Manxbuggy1 and many other home made ones which were typically calibrated using several factory lights rated specs.

The TA Tube is calibrated by some reference lights Texas_Ace sent to Maukka over in Finland to measure in his professional integrating sphere. He’s got a certified reference light source which is why we trust his measurements. Here are some of his pictures if your interested. Maukka’s Sphere

He’s got a $10k setup in his living room. Lol