Four requirements need to be met for good vision and recognition:

1. A minimum luminance (adaptation luminance) is needed to make out objects and details. Objects that can be recognised effortlessly in detail during the day become indistinct in twilight and imperceptible in darkness. 
2. For an object to be recognised, there needs to be a minimum contrast (difference in brightness) between it and the immediate surroundings. This is also normally a colour contrast and a luminance contrast. 
3. Objects must be of a minimum size. 
4. Perception requires a minimum time. A slowly turning wheel, for instance, can be clearly made out even in detail but the details become blurred at higher revolutions. A bullet, however, moves too fast to be identified at all.
   
   

The challenge for lighting technology is to create good visual conditions by ensuring that the above requirements are met. Good luminance and uniformity of illuminance in the visual field facilitates vision and recognition.