What is a question about this article? If the question is unanswerable, say "unanswerable".

In recent years light emitting diodes (LEDs) are becoming increasingly efficient leading to an extraordinary increase in the use of solid state lighting. In many situations, controlling the light emission of LEDs may be done most effectively by using the principles of nonimaging optics.

What is the best way to control light emissions of LEDs?
nonimaging optics