Near-field and far-field goniophotometry of narrow-beam LED arrays

In lighting calculations and simulations, the emission of a light source is conventionally modeled using the far-field luminous intensity distribution. However, the advent of luminaires including large arrays of LEDs with focusing optics creating narrow beams has made the traditional limiting photometric distance to reach far-field conditions less easy to determine. Furthermore, even correct far-field data can lead to erroneous predictions when illuminances are determined on a task surface which is positioned within the near-field region. A near-field representation could overcome these problems, but experimental validation for such LED arrays is lacking. This paper reports on near-field and far-field laboratory experiments using an array of two and five narrow-beam LEDs. A near-field approach makes discussions to determine the far-field photometric distance superfluous and leads to correct illuminances at any location with respect to the array, irrespective of the dimensions of the array and the beam ang...