light products - Illuminating Engineering Society

LIGHTING FOR QUALITY
The Shadow Knows
Doug Paulin, LC
YES,THIS IS A PERIODICAL
of the lighting arts and sciences in
North America. But I devote this
column to shadows. Plural. Shadows
are so important for our vision, and
not just the simple silhouette, often
referred to as “negative contrast” in
roadway conversations. (Have you
ever noticed how we have the habit
of taking a nice simple word that
everyone understands [silhouette]
and inventing a “lighting term” for it
[“negative contrast”]).
Back to shadows. My first encounter
with shadows was in a
photo studio.We were shooting new
product for catalogs and spec sheets.
We paid attention to shadows and
reflections and fiddled with other
things that can make or break a good
catalog photo until we wanted to
scream.But shadows are the visual
cues that tell us that the object in the
two-dimensional photo is actually
three-dimensional. The photographer
would often take the first 4 x 5
Polaroid snap from the camera and
say “Yep, it looks like a hubcap!” But
after he adjusted the lighting to
accentuate the depth and shape, it
would look like a lighting fixture.
Modeling is a technique of creating
varying shades of brightness, or,
should I say, varying darkness of
shadows.The modeled effect comes
from two or more sources, hitting
the three-dimensional object from
different angles and different intensities.
This doesn’t mean that the
sources themselves have to be different;
one can be farther away from
the other(s).
Playing Tricks
This brings us to the “trick” I use
most often when measuring illuminance
in the field.Pay attention to the
shadows—not just the shadow of
your head on the light meter! Look at
your own shadows on the floor.
When your own shadows are equally
dark, you are probably equidistant from
each of the light sources.To make sure,
move back and forth a few steps
either way and watch one shadow
get darker, and the other lighter.Why
is this important Because the midpoint
between two fixture locations
could be a point of minimum light
level. It then follows that a point
Figure 1
Figure 2
between four fixtures should give you
four shadows of equal darkness. (I
almost typed “equal density” which is
more exact, but not as easy to read.)
Have you ever “counted” the shadows
each football player makes on
the field This tells you how many
sports floods are aimed at that point,
doesn’t it
Another example: A decorative
street lighting project in downtown
Madison,WI, uses semi-cutoff decorative
luminaires. A colleague pointed
out that there couldn’t have been
much horizontal light generated
because the streetlight across the
boulevard was able to cast a shadow
of the fixture and pole on an adjacent
wall (Figure 1). I studied this
installation in person and couldn’t
help myself from creating another
shadow on the wall with my arm.
The light across the boulevard created
a shadow of my arm on the
wall, as expected, but where my
arm-shadow crossed the pole-shadow,
you could see that the intersection
of the two shadows was darker
than the pole-shadow (Figure 2).
The analysis My arm-shadow blocked
the light from the near fixture, as
well as light from the one farther
away, and while the pole-shadow
was there, it was not as dark because
some of the high angle light was
washing some of it out.Again, more
than one shadow can tell you so
much about what is going on with
the light, or lights.
So pay attention to the shadows.
Especially if you are dealing with
multiple sources and locations of the
luminaires. Shadows can give you the
contrast necessary for good visualization
of the scene, but they can be
a good analysis tool also.
Doug Paulin, LC, is currently with
lighting rep firm Packerland Lighting
Sales, Inc., Egg Harbor,WI.Throughout
his career, he’s worked as an independent
lighting designer and has also held
positions ranging from product manager
and marketing manager for manufacturers
including Ruud Lighting,
Lithonia Lighting, Cooper Lighting and
Thomas Day-Brite Lighting.
December 2005 LD+A 17