Homogeneity Evaluation

Posted on Thursday May 29 2014, by Zhaga Consortium

This Zhaga White Paper was published in May 2014 (Edition 1.0).

Download the White Paper

When specifying planar or linear LED modules with multiple LEDs, there is always a trade-off between low LED number and homogeneous fill factor of the plane/line of the module surface. Large LED numbers per area are associated with high homogeneity, meaning it is easy to construct a luminaire where single LEDs are not visible as single bright spots.

It is obvious that not only the LED-to-LED distance (often called “pitch”) determines the look of a luminaire that has LEDs inside, but also luminaire construction and personal sensation of the observer. Thus, there is probably no general way to assess homogeneity for all LED layout patterns, luminaire constructions and aesthetic flavours.

It is possible, however, to give an estimate of the effort that is necessary to achieve a certain look of the luminaire with a given LED pattern on a linear/planar LED module. By this estimation, a user can assess if an alternative (interchanged) LED module will give a similar, higher, or lower degree of homogeneity in the specific application.

This Zhaga White Paper describes methods to measure and to evaluate the look of linear and planar LED modules with discrete LEDs spread over their surface, such as LED Light Engines (LLEs) that are compliant with Zhaga Book 7. These methods are specifically designed to compare LLEs in one idealized application, not to predict LLE appearance in any possible application. Rather, if a user has chosen a certain LED module, he can use the data gathered with the methods described here to estimate if another LED module will result in similar, higher, or lower homogeneity in his application.

The methods give a relative ranking in one application carefully designed to give a distinctive and meaningful result. An absolute assessment (maybe also including angular dependencies or even colour deviation) would require much more detail and effort in measurement and evaluation, and is regarded as too arduous for the purpose of selecting between interchangeable Zhaga LLEs.