If you've got full cutoff fixtures you are usually set. However, if you have a situation like we had earlier, with some angled spotlights, you've got a problem. We actually took IES data and converted it using a homemade spreadsheet. We had to take candela info from the IES file and convert it to a different angle mathematically. Not an easy task! That's the hard way. I'd like to hear about the easy way!