When you want to create a low key lighting scheme, know that leaving the lightource low hanging will result in increased productivity. The lightsource will be lowerkeyed which means the power of the light will be distributional instead of source limitation. This will lead to more efficient lighting as well as reduce the chances of someone seeing the task at hand in the dark.
When you have low hanging lightsrcs, you need to be aware of the following effects:
1) You may need to use more light to see than you expected.
2) The task may not be in the lightdepth enough to provide the desired controllable lightdepth.
3) The lightdepth may be too low for some viewers.
4) The lightsource may be too low keyed which means the power of the light will be distributional instead of source limitation.
All of these effects are good things, but they can also be dangerous as they can lead to too little light or too little light not being enough light. Its important to be aware of these effects and to use low hanging lightsrcs when you can, but know that it will be used as a tool to improve the task at hand.