I have some experience using weapons mounted lights in tactical situations. However let me preface all my comments by saying I have never been in a live fire fight under these circumstances. But, our team does quite a bit of simunitions training.
The weapons mounted lights are the most versatile tactical accessories. They allow positive identification of the target and at the same time blind the target. Most types allow one handed use of the weapon - a very important consideration when setting up a tactical weapon.
I have found that intermittent use of the light is VERY difficult. It is a fine motor skill. You must think on and off while at the same time doing a deliberate threat scan and assessment. You must also accomplish this with only one eye open or you will ruin all of your night vision. Then you must immediately move because you have given away your position. This becomes much more difficult if you throw in actually shooting.
Light, threat scan, threat assessment, fire, light off , move, and repeat. Remember while the light is out and you are moving you are trying to regain your night vision plus the bad guy is probably moving also. Now yu have to start form scratch and begin searching all over again.
Our team turns the lights on upon entry and leaves them on under almost all circumstances. We use dynamic movement to reduce the risk of our lights being the targets. As for as being able to shoot the center of the light - most tactical lights put out enough light to not only blind but also to disorientate. In simunitions training I have never successfully engaged (in a CQB situation) the center of the light.
Light and movement will most always give the advantage to the team.
All light techniques should be practiced under a variety of conditions to test each individuals physical reactions to the technique.
To the best of my knowledge