Everybody uses IES lights in arch viz renderings but most people use ready made files provided by lighting fixtures manufacturers.
However, if you are in a creative mood, or just can’t help yourself from controlling every little detail of a rendering, you should definitely check out the latest tutorial from Jamie Cardoso.
In this tutorial he talks about how to create your own customized IES files with the help of a small piece of software:
http://jamiecardoso-mentalray.blogspot.co.uk/2012/12/creating-customised-ies-web-lights-for.html
