I spent this morning dialing in a conversion factor. The first problem I had was that most of my lights are modified...
I managed to find several stock lights, & corresponding numbers from experienced members/reviewers here on BLF. It's not a large data set by any means, but it seems to scale well from small to large lights.
Below are the lights I used, & lumens from my pipe-meter after conversion factor, followed by other member's data;
DQG Tiny AAA version 3; 56 lumens (~60 lumens, _the_'s review )
DQG Bullet ; 208 lumens (220 peak, JohnnyMac's review)
K50v2; 1616 lumens (1638 - 1656, K50v2 mod thread)
EE X6 SE; 912 lumens (900+, JohnnyMac's review)
Convoy S2+ triple Nichia 219b DD; 1280 lumens (1279, MTN discussion thread)
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Going from that, I appear to be "in the ballpark".