(a physical law that states that light falls off in intensity, disproportionately to the distance of the light to the subject.)
is the distance a traditional light would need to be from the subject to match the fall-off and shadow characteristics of a dedolight parallel beam light. This is calculated by tracing the angle lines of the beam back to a point where they converge.
It should also be noted that the virtual light source is
further increased when the light is redirected with the hard reflectors. This can be measured by the sum of the light passing from the fixture to the reflector, then onto the subject. In other words if the reflector is 10 feet from the source and the subject another 10 feet from the reflector then the ‚relative light’ travel is 20 feet, thus reducing the effects of the inverse square law.
However, this effect depends on the surface of the reflector. The harder the reflector, the more the virtual distance is in effect. With the soft reflectors the virtual light source is not relevant, the surface becomes the source with no indication of the distance it travels to get there.
used is either an open face light, PAR or Fresnel lens light, although all these lights have their place and are very useful in terms of control and function. They are often too hard to look completely natural in most situations and too soft to look like convincing sun rays.
The closest I ever got to convincing sun rays with artificial light was the old carbon arcs. However, since they are not available anymore, the next best thing I have found are the Mole Richardson’s mole beams, producing a parallel beam of hard light, similar to the PB70. They use a massive parabolic mirror to focus the light into a parallel beam. However, the optics and efficiency are nowhere near the dedolight PB70/30 and colour fringe appears quite badly on the edge of the beam, and the homogeneity of the beam is very inconsistent.