I see this term Photonis "High Gain" being thrown around a lot .   What is the info in these?   Is this new designation just another marketing ploy by vendors or is it a truly new design by Photonis ?  I can't stand word salad marketing and vendor made up terms.    

It would be a lot easier if Photonis would use the same numerical spec. system as L3 or Elbit to compare performance.

We buy night vision to use in the dark not to use in semi dark conditions which where Photonis seems to get all it's praise .

I readd it was their milspec tubes and the Echos were fallout from the grading process.
I honestly don't know if that's true.

They are Photonis tubes with a higher gain to compete with Gen3 tubes.

The Canadian company ColdHarbourSupply did an in depth review on youtube.
For visual comparison there is a Hoffman test that includes: Photonis Echo+, Photonis 4G High Gain, Elbi Gen 3 - it starts at 8:30.

https://youtu.be/-Ngicy5VKi0?t=511

Excellent video

At higher light, the tube brightness is adjusted.  Usually by autogating, but ABC is also active.

At lower light levels, the tubes (all manufacturers) start to operate in analog mode - this is useful with a luxmeter for estimating the local albedo levels.

The gain is entirely relevant once you get into this range, and you are limited by the 2700~2900K light source, which doesn't really match night vision in the IR region, though is a reasonable fit for Gen3.

Your eyes can compensate for a fair bit of gain difference, so brightness is a curious measure. once you get about 30,000 times, a tube is suitable for military applications.

What this experiment doesn't do, and what a Hoffman tester can't do, is replicate the night sky illumination, which is what really drives "in the field" testing.

But it's a really cool test nonetheless and I liked the video.