Flood lighting can provide a wide range of light distribution or beam spread.
Beam spread is classified into NEMA Types.

Example: If the horizonal beam spread is 120° and the vertical beam spread is 140°, then the NEMA type is 6 x 7.

Examples

Here are some examples of how this nomenclature works:

Asymmetrical Beam Spread
Actual field angle: 135° (H) x 72° (V)
NEMA Classification: 7 x 5



Asymmetrical Beam Spread
Actual field angle: 76° (H) x 51° (V)
NEMA Classification: 5 x 4



Symmetrical Beam Spread
Actual field angle: 35° (H) x 35° (V)
NEMA Classification: 3



GENERAL FLOOD LIGHTING PRINCIPLES

*A narrower beam spread should be used if there is a large distance between the floodlight and the area being illuminated.

*Narrow beam flood lights have a lower percentage of beam lumens falling outside the area to be lighted than wide beam flood lights. 

*NEMA type is determined by two angles (horizontal and vertical) where the light intensity is 10% of the maximum beam intensity.

***Above resources from internet, In case of infringement, please inform to delte.