Source Lighting Cells and IES Files
For photo-realistic lighting in images, the use of IES lighting files is supported. These are available for downloading, from various lighting manufacturers, via the World Wide Web. IES data files apply the correct values to the source lighting cells. As well, they define the photometric web, to correctly display the spread of the light from the light source, to produce more natural looking images.
How a particular IES light should be used is up to the manufacturer who defines the data. It is not possible always to tell, by looking at the IES file text, whether or not it is intended to be used as an area light or a point light. Often, however, there are some clues, as the manufacturer can (optionally) specify the dimensions of the luminaire. While these values are ignored by the rendering process, you can use them as a guide in using the IES file properly. That is, by applying it to a light source of the corresponding size. For example, to use the IES file properly for an IES light that has a defined area, you could define an area light of the appropriate dimensions and then turn on "IES Data" for the light source. Bear in mind, however, that there are provisos to applying IES data to directional light sources such as Area Lights and Spot Lights. When an IES lighting file is specified for a light source, the IES values override the current values in the source lighting cell, except that any IES light that would be outside the cone angle of a spotlight, or behind the plane of an area light, is clipped off. If this "clipped" light is important, then it is better to use Point Light sources when working with IES data. This ensures that the lighting is correctly matched to the data in the IES file.
Scene illuminated with two "standard" point light sources (left) and with IES lighting data applied to the point lights (right).
In the above images, the left image is illuminated with two standard point light sources. For the image on the right, IES lighting data was applied to the two point light sources. This changed the characteristics of the point light sources such that they shine upwards and out from the wall, producing a more natural looking lighting for the model. When IES data files are used, all settings for the light source, apart from its color, are read from the IES data, so that little or no further tweaking of the light source should be required.
Using the Drag-and-Drop Feature with IES Data Files
If you drag an IES data file into a view, the Place Light tool starts, with IES Data enabled.