Why it shines
Trace the light by hand. The top drawing looks down on a round form, with you at the bottom. Drag the bulb or use the sliders. Where a bounced ray comes straight back to your eye, you get the highlight. Where the rays only graze the form, you get the shadow core. Both drop down onto the cylinder below.
What to try
- Swing the light from left to right. The highlight slides with it, and it is never stuck to the object.
- Add rays. On the curve, each bounced ray leaves at a different angle, so they fan out. That is why a round form's highlight is a thin line, not a flat patch.
- Bring the light round behind the form. The highlight walks toward the edge, and the shadow core comes round to face you.
Drag the eye or the box. Each ray leaves the box, hits the mirror, and bounces to your eye at the same angle (i = r). Follow the red ray back through the mirror and it lands on the box flipped, the same distance behind the glass. That flipped box is what you draw.
Drag across the drawing to slide the rays. Every ray obeys angle in = angle out. Only the surface changes: smooth keeps the rays together (a sharp reflection), and wavy or rough sends them every way (a soft, matte look).
Sketch
Draw it yourself
- Draw the form from above as a circle, and put your eye below it.
- Draw parallel rays from the light until they hit the circle.
- At each hit, draw the normal: a line from the centre out through that point.
- Bounce the ray so it leaves at the same angle to the normal as it came in.
- The bounce that heads to your eye is the highlight. The rays that just graze the edge mark the shadow core. Drop both down onto your cylinder.
Videos
Videos on light, highlights and the shadow core are on the way.