I think you will see the problem yourself if you remember that for an NPN transistor to pass large currents from the collector to the emitter you must cause current to flow into the base terminal. Because there is a PN junction between the base and the emitter, it is therefore necessary to raise the voltage of the base terminal about 0.6V above the voltage of the emitter terminal. Don't make the mistake of thinking that you just need to bring the base to a voltage about 0.6V above ground. That's a common misconception because you usually see the NPN transistor used with its emitter tied to ground.

You can also think of this from the emitter's point of view. If the voltage at the emitter starts to rise for some reason then the transistor will stop conducting current once the emitter voltage rises to about 0.6V below the base voltage. So, the emitter voltage can't ever be higher than the base voltage when the transistor is conducting. Now, think about the voltage you are using to turn the transistor on and off. The emitter voltage must always be lower than that voltage.

BJT switch connections
I shot at a concert for the first time. The pictures were pretty good for the capability of my equipment, but on some shots, the light has a very strange flare. It isn't the usual rays, but some soft, non-symmetric form which I find quite strange, and, on most shots, distracting. 



On this image, you can see it just above Gino's head and also behind his back, to the right of the mic stand. I am not sure if the slight blue lines on the left side of the picture (they form a triangle aimed at Chris's head, maybe not visible on all monitors) are part of the problem or if they come from a different light source. 

What makes them appear, and how do I avoid them? 

I shot with a D90 with a 18-200 lens, no filters or hoods attached. The settings were quite strained (iso 3200, often at max length and max aperture for the length. This specific picture is 1/125, f 5.3, 95 mm). 
