Not sure of driver diameter - wasn't in my notes. Uhhh - Simon's drivers won't work with this light - his drivers are for power switch lights, not e-switch lights, unless you have some way of converting it.
After reading the posts more thoroughly, I'm not sure why no one is saying this, but in any color other than green: Don't Buy This Light, unless you can control max amps via batteries or adding resistance, know what the LED can and cannot take. Another words, Don't Buy This Light unless you know what you are doing and getting.
I was fortunate to order one in green, so it works well with high amps.
The driver is completely wrong to use across all LED colors. These NM1 color LED's all have their own optimum amp range, and this driver could care less about that. If it maxed at the lowest common denominator, at least you could say they did the best with what they got, but from all these posts it sounds like most colors, including white, are over powered depending on the cell of course.
We know the white does best in the 4.5 to 5.0 amp range, so if you measure more, it's wasting power, losing output.
Astrolux/Mateminco didn't think this one out. freeme should be aware of these shortcomings now. Let's please ask them to stop selling this until issues can be worked out. Dunno if it's possible for them to do so quickly, but this needs some re-thinking.
The SST-40 version is a great deal btw - no modding required .