Beam Angle (Beam Spread)
Beam angle or beam spread is the term describes the angle between the two directions opposed to each other over the beam axis for which the luminous intensity is a certain fraction of that of the maximum luminous intensity. The amount of that fraction needs to be given in each specific case. When the fraction is 50%, the angle is called beam angle. Beam angle is also called Full Width Half Maximum (FWHM). Beam angle determines how wide (size of the light spot) and how bright (illuminance level) the illuminated area can be, and also, how far (the propagation distance of the light) the light can reach.
Narrow beam angle (usually 3°- 25°) is often applied in landscape lighting to emphasize the linear structure of building parts. In another case it is also effective to illuminate objective or area in long distance, for example, flashlight or high power spot (flood) light in stadium lighting.
Medium beam angle (usually 30-60°) is the majority of general lighting application in daily life. It takes care of both light intensity as well as lighting scope. in industrial lighting field most high bay light is with medium beam angle. Along with the development of LED technology, the advantage of excellent directivity and the feature of easy light shaping of LED has been greatly utilized.
Wide beam angle (above 60°) is usually designed to create an equal bright space without dark area and to avoid illuminance difference. T8 fluorescent light bulb is a typical wide beam angle light source. Most LED flood light are also with wide beam angle, but by mean of secondary light distributing technology (by lens or reflectors), LED flood light can be narrow beam angle too.