View Full Version : CG lighting vs GI lihgting for lack of a better Term??

10 October 2012, 07:12 AM
Hey guys, this one's been bugging me for a while I'd like to consider what the best terms to use would be when teaching lighting and lighting principles.

Outside of different renderers own terminology conflicts like areas lights being a special array of lights in some apps versus a Environment light portal in others which then conflicts with the fact that some renderers do in fact call those portals.

So the two classifications I'm trying to find the best terms for would be light source objects and illumination source objects. Light source object being your standard traditional Point, Spot, IES, Infinite/directional etc. Illumination source lights being GI emitting objects and Portals and Environment/IBL lights.

Typically at the studio we refer to these as cg lights and Area/ENV lights (again their GI portals are called area lights)

With C4D I've typically referred to them as Lightsources and GI, but I've also encountered several students (my students nowadays are industry lighters not new students) Seem to all have different ways of referring to the two categories, but the older light sources are most typically referred to as CG lights, but I find newer students are confused by that as all lights are technically CG. for the GI based portals and environment lights I've heard so many typically referring to the GI types etc, but I've also heard them called physicla lights, Or real lights as well.

What do you think the best, and clearest new term would be for these two categories?

10 October 2012, 12:27 PM
imho the clearest delineation is "delta lights" for old-school point, spot, directional etc. and "area lights" for sources that actually have an area (env/ibl, quad, sphere, disc etc.). I know a couple of other shops do the same.

The "delta light" term is slightly esoteric and comes from the fact that these types of sources are represented mathematically (in physically based rendering) using a delta function due to their having zero area.

I've also used "point sources" and "area sources" in the past, but this can get confusing because of the pre-existence of the pointlight... this sort of thing is really tricky due to a long history of bad nomenclature in CG.

A more accurate term for delta lights might be "naughty lights" since you really shouldn't use them at all in physically based rendering :)

10 October 2012, 12:58 PM
I just call lights by the function they're used for in scenes.

10 October 2012, 06:47 PM
I just call lights by the function they're used for in scenes.

Well that ties in more to theory, Things like keys and fills and how to light, but when teaching about the settings and behaviors, you need to classify them and easily refer to them.

Delta lights is an interesting term, require s a little explanation but less confusing than cg lights.

Your "naughty lights" is a prime example of why one needs to classify these. While I'm not a big proponent of the always be physically based, it is a key concern in understanding rendering methods. We have a feature that is being more strictly physically based and as such only using Area lights not the "naughty lights" so in development and training this is where our studio suddenly had the need to refer to them easily and happened to start using cg lights and area lights.

Thanks for the feedback

10 October 2012, 07:29 AM
For me, direct light vs. indirect light makes the most sense.

11 November 2012, 08:58 AM
For me, direct light vs. indirect light makes the most sense.

Agreed. Also, direct lighting can further be sub-catagorised into physical and non-physical lights. Non-physical being legacy or 'old-school' lights. Physical being photometric/area lights.

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11 November 2012, 08:58 AM
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