No, it does not. The attached does such a thing, ambient full white with vaue 400 to get a comparable lighting level in the room, and splotches all over the place: see the image - made at HIGH QUALITY render settings!!

Even when all four quality parameters are set to the max (as in the standard FireFly render settings window): splotches.

Hence the basic lesson is: when IDL rendering, hotspots on objects by extreme lighting level should be avoided, even when these are out of the camera view. Whether the extremes are caused by inverse quare direct pointlights or by hi-ambient IDL sources. Whether you drill holes in the ceiling out of the camera view, use light-absorbent materials on the walls or apply spcific attenuation profiles for the direct lights themselves: as long as the hotspots are avoided you're fine. And... when direct pointlights are used, really high quality settings are a proper way out when the other options fall short or are unapplicable for whatever reason.

Whoops...sorry bb...missed that ;). Thanks.

Laurie

Quote - It doesn't look any different than a straight inverse square, except within 3 radii.

I've been playing with different radii and test scenes with that light shader and... wow. I'm completely surprised that there is barely any difference, no matter what the radius is set to.

One of my first reactions was "Is the formula actually working?" and to test that I set the radius so that it encompassed my entire enclosed scene. There failed to be any light at all, which meant that every polygon in the scene was being calculated correctly as being inside the radius and, because your implementation of the formula is producing negative intensities or is simply bottoming out at zero---either way producing visually black---then it looks like it's working as predicted.

Now, before trying this out, I would have made a (kind of educated) guess that there would be some kind of discernible continuum from constant to inverse linear to inverse square along which all real-world spherical light sources could be placed. In theory, this still holds but really........... the visual differences are so slight from one type of light to another that it's not even worth worrying about; they almost all look like inverse square fall-off!

Perhaps the mistake I was making was in thinking of those points along the continuum as being real-world things but actually, they're theoretical objects. Constant = the light source is an infinite plane; inverse linear = the light source is an infinite one-dimensional line; inverse square = the light source is an infinitessimal point. I guess in the real world, all the possible types of spherical light source we're likely to encounter live in a very tightly grouped spot up near "exponent = 2" where the differences are minutely subtle.

Big thanks for posting the light shader and allowing me to find out and correct my faulty impressions!

John,

just read my posts above and look at the graph.

in the real world it hardly makes a difference for lightbulbs unless fixed to the wall, but it sure does make a difference for light coming from shopping windows in a street, as "about three times the radius" (or window size) is enough to cover a pavement along the shops, but from halfway the street itself things start to be inverse square again.

Quote - Big thanks for posting the light shader and allowing me to find out and correct my faulty impressions!

Hey - I was surprised, too at the visual consistency. The part that actually matters is the clamp, not the falloff curve.

Quote - just read my posts above and look at the graph.

That addresses something slightly different from what I was looking at.

BB's shader uses a formula for working out the attentuation for spherical light sources. They behave (well, the way the math works for determing how light emits from them behaves) in a particular way within 3d space. A shop window, as in your example, is not spherical, so I would expect it to behave in a slightly different way. And it does.

The shape of a light source is important as well as its size. Since spherical light sources are identical from the perspective of any target object then they follow a fairly simple function. When you bring in shop windows, and all other kinds of light-emitting objects that can have a variable profile presented to a target object, things get a little more complicated. To compare a light-emitting shop window kind of set-up with an equivalent Poser light displaying the appropriate attenuation function, you would have to create a shader to apply to the light just like BB's but it would also have to implement a different formula that doesn't merely rely on radius or, in the case of the built-in Poser ISF option, an even simpler function, and which takes into account the profile of the object as presented to the target object.

(I also think that the results your graphs and experiments are showing could easily lead someone to interpret them incorrectly, into thinking that the fall-off of a non-spherical light source can change in its underlying function of attentuation from one extreme (inverse square) to another (constant; no change) as a result of its distance from the source, but that discussion will probably drop into deep mathematics and be of no relevance to anything one would be willing to do in Poser.)

the formula presented is the exact solution for any light-emitting disk with radius R >0 at any distance d >0. Of course there might be a very mild difference with a rectangular shopping window, and there might be a mild difference with a really ball-shaped lightbulb at very short range. I'm happy to create the specific formulas for them.

Any way it's a vast improvement over the generic 1/(a+bx+cx^2) aproximation with undertermined a,b,c presented elsewhere, and a vast improvement over the infinitely small physically non-existent point size lights.

In all cases, it shows constant lighting levels nearby which can be defined as say d< R, inverse square far-off behaviour which can be defined as say d > 3*R and a transition in the middle. So yes indeed, the falloff curve varies with distance from the source.

A shopping window at 10cm will be experienced as an infinite plane while the same window will be experienced as a point light when seen at 1000 mtrs. As a lightbulb at 1 mm from the bulb behaves like an infinite plane, and as a perfect point light at 10 mtrs. As a consequence, only the transition area R < d < 3*R will mildly depend on the shape of the light emitter. For Poser users this means: one function serves all, except for the extremes like long light strips.