The source_radial is the simplest way to enter data from a manufacturer's datasheet. Here for example is the luminous intensity of the Luxeon Emitter Red (LXHL-BD01), as provided on the product datasheet. The "batwing" nature of the angular profile can be clearly seen:

Angle (degree) Relative Intensity (Arbitrary Units)   0  60  5  60  10  60  15  64  20  68  25  72  30 90  35 100  40  95  45  85  50  60  55  25  60  9  65  4  70  0  75  0  80  0  85  0  90  0

In the attached zip file (which can be downloaded from the last page of this article) there is a file, radial_source.zmx. This file contains just two objects: a source_radial and a detector. The source_radial is a flat, rectangular or elliptical shaped object which emits rays with an angular distribution given by the supplied data 



{Note that the source_radial allows the angular data to be made variable, and hence we can optimize to identify the desired angular performance for a given application. We will not use this capability in this article, as we are aiming to describe as fully as possible what the experimental data is. But, this is a fantastically useful capability when we are at an early stage of design and need to know what kind of distribution we need.}

The manufacturer's data sheet tells us that the source is 6 mm diameter, and has a typical output of 27 lumens: this data has been added to the source_radial as well. With 30 layout rays and 10 million analysis rays (remember layout rays are used only for the layout drawings: analysis rays are used for the detailed computations) we get:



Looking at the data in more detail we can see the spatial and angular performance of the source:

Spatial Data (Illuminance, in Lux)	Angular Data (Luminous Intensity, in Candela)

There is excellent agreement between the computed Luminous Intensity and the manufacturer's datasheet, but there was no data provided by the manufacturer on the illuminance of the LED (the spatial structure of the LED). Therefore ZEMAX has assumed that the source is uniformly bright across its 3 mm radial aperture. In the absence of better data, this is all we can do. To improve the quality of the simulation, we need both the angular and the spatial data: this is referred to as source radiance or source luminance.