I saw a reference to this in the Daz3D C8 video on Youtube and got curious about it. So of course I went to the manual to see how to use it... um... OK I woke up and started playing with it. Very interesting results (two camera views of same scene):

Here are a few observations. IES files are sometimes portrayed as holding more info than they really do. They appear to only describe the relative attenuation of the light. In other words, real artificial lighting has a lot of hot and cold spots that we don't consciously see but we in fact ARE accustomed to seeing. So adding these patterns to our lighting will add a subtle something that enhances realism. Interestingly, the use of IES parameter files doesn't seem to add any time to renders - in fact renders may run a tiny bit faster!

A surprising number of places post free IES files for download. They are intended to help designers select (and correctly place) lighting for architectural projects. The two sources I found most useful were GE Lighting and Lithonia Lighting, both leading manufacturers in the lighting industry.

A MUST download tool if you want to use this stuff is the free GE Lightbeams tool. (The download link is near the bottom of the page.) It allows you to see the light patterns of any IES file you might want to use (not just a GE file!) and gives you info essential for setting up a light in the scene. (More on this below...)

An IES file will NOT set up any basic lighting parameters such as color, angles etc., so here are some general guidelines to get you started:

• Type of light: In almost every case, IES lights are describing a specific type of bulb in a specific type of reflective receptacle. In C8 this translates into: spotlights. There ARE a few IES files (like for CFL's) for bare bulbs, these are the only ones I would recommend for use with a Carrara bulb. Technically, it is possible to map IES files onto ANY type of Carrara light (including Anything Glows) but you will not get very realistic results. EX: When I mapped streetlight IES files into bulbs, I got weird sidways projections of extreme lighting hotspots like spotlights shining down the street.
• Color: Set to match the type of lighting you are portraying - yellow for sodium, blue green for mercury, bluish white for fluorescent etc.
• Half-Angle: Use the Lightbeams program to get the "Beam Angle" for the intended IES file and enter half this amount into the half-angle. It doesn't have to be exact, but I've found it looks more realistic if you try to stay close to the actual angle engineered into the light/receptacle.
• Angular and range falloff: While the IES file does a good job of mapping the relative hot and cold spots within a beam, it does nothing to heighten realism at the edges. I found setting these to somewhere between 5 and 10 degrees worked well on the street lights. Maybe use these as a starting value and then adjust to suit your particular scene.
• Range: The default of 400 feet isn't very realistic unless you are setting up a 2,000 watt light! I set for 60 feet and that seems to work OK.
• Soft Shadows: I didn't see a noticeable improvement in light presentation but it added a LOT of time to the render. In fact, the image seemed to lack a bit of snap, so I recommend trying your scene without this one first.
• Photometric Profile: Load your IES file. I have no idea what the "Quality" parameter actually does or why it is set to default at 15%. I set it to 100% and it did not seem to add anything to render times.
• Light Cone: This may just be personal preference, but I thought the light looked just a touch more realistic if you have this enabled even with a really low value. Between 5% and 15% seemed to work for me.
• Brightness: You definitely want to set this AFTER you apply the IES file. Some of them seem to abnormally dim or strengthen the light, so you will definitely need to adjust back to the proper value. The effect seems to vary from IES to IES, so this will have to be trial and error, test renders.

Anyway, this is what I came up with! I hope it adds another tool in your lighting toolbox - that it gives you another way to add realistic lighting to your scenes!

Larry