How to Eliminate the Donut hole on a L4

[analogguy]

A store that I know just started carrying Surefire flashlights. I've never seen a L4 before so I asked to see it. The storeowner is telling me how bright the thing is as he hands it to me. I shine it at the wall and comment on the donut hole in the beam. As I hand it back to the storeowner, he still has it shining on the wall, I ask him if this light is bright. I pull out my Aleph 3 (LuxIII, DB 917) and put a bright white, blazing spot to fill in the donut hole. The store owner, jaw on counter asks, "What the hell kind of light is that?" I give him the quick 411. I then started swapping parts between the 2 lights (tailswitch, head) and he is floored. He is twisting parts and cannot believe that there are other flashlight makers that match or surpass Surefire quality. My trusty Aleph 3 is my WOW light. Thanks Don!

 

[Miciobigio]

Well done , Analogguy !! /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/grin.gif
I enjoy reading your post /ubbthreads/images/graemlins/thumbsup.gif

 

[Steve C]

Ya know, I've been reading a lot about this so-called "donut hole".

I got my L4 yesterday, and I gotta say this "problem" is basically a non-issue, as far as I'm concerned.

Jeez, guys; some would complain if you hung 'em with a new rope... /ubbthreads/images/graemlins/banghead.gif

 

[Chop]

The donut hole is usually caused by the emitter being too close to the reflector. The donut hole is more prevalent in some L4's that it is in others. The problem can usually be alleviated, or at least minimized, but spacing the emitter about ).020" farther away from the reflector. What this means for the L4, is that you'll need to find some very thin aluminum or copper washers and place them between the sink and reflector housing. The screws holding the sink to the head are more than long enough to do this with.

 

[brightnorm]

Strangely enough I find my Aleph/5w beam most impressive when I adjust for a subtle donut hole, similar to my brightest KL4. It's not as asesthetically pleasing as when perfectly focused but it seems to be more intense. Two non-flashaholic friends had the same impression. It could be that a higher proportion of the total output is concentrated in the beam's central portion with correspondingly weaker peripheral light. The non-donut beam may have a more evenly distributed total output. This is just a guess; I haven't tried to analyse it yet.

Brightnorm