Re: Surefire MN20 arrived!!!
Ray of Light,
The MN20 should work fine on two Li-ion cells, provided they can deliver the current.
OK.
Got my new MN20 today, and I see immediately what they did to create the new design. It looks very much as if they simply added two extra turns to the coil, going from 12 turns to 14.
If the CCT (and thus average filament temp) remains the same, and you increase the length, then you increase the voltage. But if the voltage remains more or less the same (which is the case here), then increasing the length, and keeping everything else the same, decreases the CCT.
If we estimate that the new filament is 14/12 as long as the old one, and that the old filament had a CCT of 3400 K when driven on 2p3s 123's, then if the new filament is driven 7/6th times the voltage of the old one, it will have the same CCT. Which means that the new CCT will be the old CCT times (6/7)^.42, which will equal 3187 K instead of 3400 K.
This equates to an efficiency loss of about 6 lumens/watt. The MN20 is about an 18.6 watt lamp, which will mean (assuming the power of the new MN20 is the same as the power of the old one--which is by no means certain) a loss of 112 bulb-lumens = 72 or so torch-lumens. However, given that the old MN20 was about a 400 lumen lamp on fresh batteries, this still means that the MN20 is above its rated lumens output value.
But these are just preliminary guesses on the subject. I will need to measure current and voltage of old and new MN20's to say something definite.
Well, I can definitely say that the new MN20 filament is longer by just about a 1/6th. And it looks to be the same thickness, and the coil winding diameter looks to be almost exactly the same.
All of this makes sense, in that if you keep everything else the same and make a filament longer, you lower the CCT.
However, I really was hoping that they would have kept the filament exactly the same and just put it in a larger envelope. After all, the problem with the MN20 wasn't that it was driven too hard and had a short life span, or that it was instaflashing at turn on.
No. The problem was that they were exploding. This has to do with the power density within the envelope, and envelope temperature, and the type of glass, and whether there were any flaws during manufacture, and so on. Lowering the CCT will certainly help mitigate these factors, but making the envelope larger would seem to me to be a more direct way to solve these problems.
And then the efficiency loss wouldn't have been nearly as great. Ah well. Figures I guess. The MN20 was such an overdriven lamp that it's miraculous it was ever designed and sold that way. I'm sure glad I have an old one installed in MY M6. It's going to stay there for the forseable future, I can tell you. I just love that lamp.
I'll report more when I try out the new MN20 to see how white it is and how it compares to the old one.
:naughty:
