help with lighting

Robert Wechsler (r.wechsler@rzmail.uni-erlangen.de)
Tue, 12 May 1998 09:07:26 +0200

Dear Group,

As I recall, there were some pretty savvy stage-tech people in this group...

Maybe someone can give us some tips?

As is true for other interactive systems as well, lighting can be tricky.
The light does not only have to satisfy humans but also a computer. Some of
our interactive systems (notably touchlines) depend on adequate contrast
between the dancers and their background -- floor, and back wall. There are
three camera positions: overhead, 5-7 meters up in the middle; and two more
are head-high at the downstage corners.
Since theaters are usually pretty black places, we usually go for
"light-against-dark", ie. light colored costumes or skin.

There are still three major problems:

1. reflections off of marley floors
2. shadows
3. too little contrast in the corners

Down-light (from above) reflects on the marley floor back into the lens of
the overhead camera, sometimes overloading it. front light has no
reflection problems but creates shadows. the computer can easily confuse
these with the dancers. you might think: well, why not just use a lot of
side light. ok. this is largely what we do. but the thing is the cameras do
not see what the public sees. For example, when a dancer is at the side of
the stage, the angle of the camera is such that the camera does not "see"
the effect of the near side lights, only the far ones. furthermore, because
cameras "see" spherically, the corners of the stage are farther from the
lens and thus receive less light, and, more importantly, less contrast
(inherent in greater distance). the only solution would seem to be to
better light the corners (we did think of a software solution, enhancing the
perimeter lighting, but the factor is "contrast", and this is difficult to
enhance.)
high diagonals crossing to the corners, when barn-door shuttered (solving
the reflection problem) can add to the corner light in a way which is
effective for the camera, but when they are hot enough to solve the
dark-corner problem, then they are also shadow makers.

Thus, we usually rely on lots of side light, with higher levels and more
instruments for the most down and upstage alleys. Plus an out-of-focus wash
from above, high side, front and back, with each instrument set to its
maximum level which at which reflections do not occur. When all are
balanced, and none is too hot, you get many overlapping weaker shadows which
the camera can survive.)

One idea suggested to us is to use indirect light sources. We did this to
make our video: we aimed lights (pointing from the stage outwards) at 3
2-meter styrophone boards mounted at floor level DOWNSTAGE, ie. where
obviously the audience usually sits. wouldnt work for a show. Frost
filters seem to have no real effect on our system. they soften the edges of
a shadow, but they do not seem to actually lighten it at its darkest points
(in any case they had no effect on the problem.)

There are different kinds of special lights for low-shadow work. They can
be pretty distracting from the audience's perspective, but hey, we're in no
mood to be too fussy. but would they offer enough light?
Fluorescent lights (work lights) are also not bad, though the reflection
problem arises as they are often located directly overhead. (and in any case
the quality of the light is ... an acquired taste.)

Not all of our work uses touchlines (thank goodness), and some touchline
pieces use only the horizontal cameras (these are rarely problematic).
Still, for these parts of the show, I think you get a whiff of the sort of
challenges we are facing.

regards,
Robert

"More light!" (- Goethe's dying words.)

I wish it was that simple...

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Robert Wechsler and Helena Zwiauer Phone: (49) 911-397472
Palindrome Dance Company Fax: (49) 911-397472
Johannisstr. 42 / 90419 Nčrnberg
HTTP://OURWORLD.COMPUSERVE.COM/HOMEPAGES/PALINDROME
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~