Rendering many overlapping parallel lights In my situation, I want to render many narrow spotlight all overlapping in mist. 



You can see in this image how all the spotlights overlap. The rendering I'm trying to produce is a simulation, and therefore I want to keep the geometry mostly as it is.

I've tried a few approaches:

Use spotlights into a volume

The issue here is that the minimum angle of a spotlight in Blender is 1 degree, which is still too large for me! (My spotlight should be 0.5 degrees)

Blender Render / Volume emit cylinders + Scattering volume


The main issue with this approach is that in areas of very strong overlap, some bits are even darker than background. I.e. where there's lots of light crossing over, the result is shown as dark.

Perhaps the 'emit' object are also casting a shadow.

Cycles Render / Volume emit cylinders



Get a better result (the areas of most overlapping aren't the darkest). But still getting some black parts.

For Blender Cycles, I also tried disabling Ray Visibility settings on each beam object for


Transmission
Volume Scatter
Shadow


but the result is largely the same
For Cycles volume emitters you need to ensure that the number of bounces in the Light Paths panel is set sufficiently high - otherwise the rays cannot travel through all of the surfaces.



The Transparency Max and Min values determine how many transparent surfaces rays can pass through. Increasing both values will allow rays to pass through more transparent surfaces unaffected.