The issue of LEDs light distribution

Diodes are manufactured in different housings with different initial optical systems. Each of it, differently shapes the distribution of luminous flux. Generally, typical distributions can be divided into 4 basic groups:

  • narrow distribution
  • lambertowski distribution
  • wide distribution or batwing
  • lateral distribution or side emitting

The basis while choosing an appropriate diode for the particular usage is the indicated photometric data included in the catalogue card, however for the purpose of rapid commercial classification the simplified breakdown of diodes was implemented due to the nature of the distribution of luminous flux

Diodes have photometric bodies with rotational symmetry represented through the average light curves. The parameter describing the nature of distribution which is indicated by manufacturers is the distribution angle (useful divergence V1/​2).

Narrow angle diodes are characterized by the distribution angle not bigger than 90º. Often obtained diodes are the ones with the distribution angle from 15º to 30º.

The perfect Lambert distribution is characterized by the angle of 120º. Diodes which refer to the group of Lamber diodes have distribution which is only similar to the ideal one. The biggest differences occur in case of wide lighting angles. Diodes of such group would be described by the distribution of angles from 110° to 130°. It is the most frequently obtained distribution angles among the SMD diodes or high power diodes.

Wide-​angle distribution named also as butterfly is characterized by the angle wider than 120° as well as the fact that the maximum brightness has different direction than the optical axis, tilted from it at 30° to 60°. It frequently occurs among the high power diodes.

Side distribution is characterized by the angle wider than 180° as well as is tilted in the direction of maximum brightness at more than 60° from the optical diodes axis. Due to the complicated structure of the initial optical arrangement realizing such distribution, it is not so frequently obtained and occurs only among high power diodes.

In practical use, in lighting equipment not single LED diodes are being used but prepared LED modules. In such cases the manufacturer of the final equipment indicates the resulting lighting distribution similarly as in case of traditional lighting housings. Having in mind ways of LED lighting, it is worth to remember about the illumination problem. The whole luminous flux of diode is emitted from the ground of a few square millimeters. The illumination of this ground accounts for in dependence on diode’s construction and the power of its working from several up to more than 50 millions cd/​m2. It is important to carefully conduct the analysis of possible dazzles for LED lighting and installation.