Another consideration you will wanna be aware of and practice is reloading and clearing malfunctions while holding a handheld light or having a weapon mounted light on. Depending on the circumstance, you may wanna practice turning off the light before performing any manipulations. This would be good so you do not telegraph your position or point the light in an area that will cause you to flash and possibly blind yourself. When using a handheld light, manipulations and reloads are going to obviously be a bit of a juggling act at first. However, I found that it is not too hard to pick up a personal technique for retaining the light in my hand while conducting manipulations.
Just remember that low light is a huge sensory deprivation situation and mental soundness will be key. Practicing until these manipulations are second nature and don't require visual concentration will greatly reduce your stress and help you concentrate on saving your life.
Let us just say that I would prefer to let the situation dictate my method. Distance will determine the time I have, and if I am close or my response time is strained, I would opt for keeping my handheld light in favor of getting my gun out faster. However, if time and distance permits, I think it is fine to just say good bye to the handheld and take the extra second to activate the pistol light. However, if I am using a handheld light and drawing my pistol becomes necessary, I doubt I am going to feel that any extra time can be spared. However, knowing when you will have time to switch to the pistol light, if you have one, would be good to practice.
Training is not the only time you should practice this stuff, but rather an initial push to show you the type of things you can do to get better and to see where you are at. That said, do what you can to get training other than articles, books, and my YouTube videos. Nothing can substitute an in-person class with a team of teachers and students to give you a healthy learning environment. With all that said, I look forward to writing about what I have learned and hearing what you think.