Lighting Question

[wfcentral]

I am having a conversation with a co-worker about the properties of light on cylinders. Can someone please help clear this up? I have posted an image that I whipped up in Xara X to illustrate the two views. I know that the tops of the cylinders are not shaded correctly...I'm more interested in the sides.

The question is. If light is hitting a cylinder at a 45 degree angle, will the cylinder be evenly shaded top to bottom like the cylinder on the left or will it have a diagonal shade like the cylinder on the right??

Thanks,
Robert

[wfcentral]

I am having a conversation with a co-worker about the properties of light on cylinders. Can someone please help clear this up? I have posted an image that I whipped up in Xara X to illustrate the two views. I know that the tops of the cylinders are not shaded correctly...I'm more interested in the sides.

The question is. If light is hitting a cylinder at a 45 degree angle, will the cylinder be evenly shaded top to bottom like the cylinder on the left or will it have a diagonal shade like the cylinder on the right??

Thanks,
Robert

[Peter P.]

I just wondered how you could ever consider anything different...

[Steve Newport]

If the light covers the entir length/width of the shape, then the fall off will be a verticle blend(ex. #2 below).

If it's a smaller source like a flashlight, for example, that doesn't cover the entire shape it wouldn't be either of yours. The fall-off of the light to shadow will be an elliptical blennd (ex. #1 below)

Hope this makes sense!

Steve Newport

[gwpriester]

Steve

Your illustration is very good. To add a bit more realism, I like to had the far side a bit lighter to represent reflected light. The darkest part of a cylinder is usually next to the highlight as you have illustrated it.

Gary

Gary Priester

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[Peter P.]

<BLOCKQUOTE><font size="-1">quote:</font><HR>Originally posted by Steve Newport:
It depends <HR></BLOCKQUOTE>

Wfcentral's question was, I quote:
"If light is hitting a cylinder at a 45 degree angle"

Maybe you should try to read next time.

[gwpriester]

Best to keep quiet and have people think you rude, than to open your mouth (virtually of course) and prove it! [img]/infopop/emoticons/icon_razz.gif[/img]

Whereas the first example may be theroetically correct, Steve's second image, in my opinion, looks more natural and is more believable. If you know anything about art history, you know that historically artists have taken the path of what looks natural and believable as opposed to the anatomically correct path.

Gary

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[roman]

Maybe just...

Peter Pan sees a closed the closed (not hollow) tube.

Steve sees tube which is opened at the top.

Then, of course, if we think about closed top of the tube, Peter is right while Steve is right when we regard the top of the tube as opened and tube is considered being hollow. (uh.. I speak somehow weird today ;-))

Roman

[Steve Newport]

Mr. P, nice to see you back again, hope you had a Merry Christmas or chanuka or Kwanza, whatever you celebrate. BTW, Steve is fine for the salutations.

Just one little thing before I start my explenation, you quoted me saying...

[QUOTE]Originally posted by Peter P.:
Quote: "Originally posted by Steve Newport:
It depends "
QUOTE]

I only said "Depends", how bout you start reading!

Anyway, my explenation is quite correct. In both of my illustrations the light is coming from a 45 degree angle, Just in one case, the 45 degree angle light is not completely covering the cylinder. I made a picture for you just in case you're mind can't comprehend these words (See below)
Here, try it yourself. Hold a flashlight at a
45 degree angle over a cylinder (A cup or a mug, be creative) in a dark room so that the the edge of the light is at the center (Highth-wise) of the cylinder. You will see that the fall-off is, in fact, elliptical!

I hope you understand now!

Think before you speak Petie, you might not be held as such a moron then!

Roman, I'm not really seeing what you're saying!? Maybe I'm just stupid, I dunno!

And Gary, I have quite the same outlook as you. In art, what looks right is better than what is correct. Thanks

Steve Newport

[Mickie]

So can't test your example Steve. However it sounds like Robert's original question can't be answered without knowing the light elevation... there is always one more detail [img]/infopop/emoticons/icon_eek.gif[/img]

Roman, does the shadow on the back of the object really change depending on whether the object is hollow or not? I quess I see (if hollow) how a reflection could change the light in front (bouncing back from the inside??), but would it effect the back?

I'm going to have to find a dark room, batteries and a cylinder somewhere [img]/infopop/emoticons/icon_biggrin.gif[/img] [img]/infopop/emoticons/icon_biggrin.gif[/img]

Mickie