Optics

CONTROLING LIGHT:
When light strikes a surface, it either: passes through (transmits) is absorbed is reflected

Reflection
Lights reflects at an angle equal to the angle of approach

Angle of Incidence=Angle of Reflection

Nature and quality of reflection

Dependant on the surface
Specular reflection: polished surfaces
Diffuse reflection: matt surfaces
Mixed reflection: elements of both

Reflectors:

used to direct light and improve efficiency of light sources.

Flat reflectors add efficiency, but in uncontrolled manner.
Greater efficiency is found using geometric reflectors.
Different shapes have different qualities and uses.

Curves and focal points

Regular curves have definable focal points
Light reflection most predictable and efficient at focal points.
Spherical reflector:
Parabolic reflector:
Ellipisoidal reflector:

Refraction:
Light bends passing from one medium to next.
Thinner to denser, bends towards normal
Denser to thinner, bends away from normal
Parellel material, the two bends cancel. Path is parellel but not quite in line.

Prisms:

When surfaces are not parellel, the path is deflected.

Different wavelengths bend at different amounts. Were rainbow comes from.
Happens in lighting instruments, too. Shows up at the edges of a beam.

Lenses:
Flat surfaces are prisms.
When surfaces of prisms are curved, they form lenses.

Concave and convex surfaces.
(Also true of mirrors)
Convex lenses- surface curves out, act as magnifiers

Concave lenses- surfaces curve in; act as reducers.

Focal points Most common lenses use spherical surfaces.

Plano-convex lenses/ PC lens: Most common lens in lighting instruments.
The greater the curve, the shorter the focal length
Efficient but heavy, breaks from heat stress.

Reducing the thickness of glass reduces heat caused breakage.

Multi-lens approach.

Fresnel lenses: preserve curves but reduce material on curved side.
Rings may show, dappling added to planar surface.

Step lenses: reduce material on planar side

Diffraction:
as light passes around an edge, it bends at edge.
Not significant in stage lighting.
Effects are there (fuzzy shadows),
but of so small a scale as to be insignificant.