Egg Crates are a valuable accessory for soft light sources. Shaped like a
3D grid, they are available in different strengths, differentiated by their
angles of dispersion. So a 40 degree egg crate will limit the dispersion of
the soft light to 40 degrees.
Due to its wide front diffuser panel, the output dispersion of a soft light can
approach 180 degrees, even tho' it's beam angle (the brightest center part
of the beam) is closer to 90 degrees. This can lead to light spilling on
areas of your set where you dont want it. The solution used to be large
flags positioned on stands & boom arms to keep spill under control, but the
fast world of location work made this impractical.
With the introduction of the, fast & easy to attach, fabric Egg Crate, it has
become much easier to control the spill of soft lights in smaller spaces. By
using several smaller grid cells, an Egg Crate only needs to be a few inches
deep, compared to the much larger barndoors or flags that would be
needed for a similar effect. While it does not have the definitive shadow
edge that a large flag would create, they are very effective in keeping spill
from building up from on lightly colored walls, which can happen when
using numerous lights.
The resulting edge fall-off is very gradual, and that quality can be put to
several unique uses:
If you start to pan the light slightly away from a subject, you will see the
light appear to dim as the Egg Crate grid cells begin to limit the amount of
light striking the subject. Because you are not lowering the power to the
lamp to cause this dimming effect, the color temperature doesn't change
as it would if you used an electrical dimmer. With two softboxes as key and
fill you can adjust their individual brightness very quickly.
You can also take advantage of this gradual fall-off to provide a natural
decrease in light intensity as a moving subject comes closer to the light.
This keeps the image from becoming over exposed as would normally happen
when a subject approaches a light source.
Be aware that there is some loss of output when you use an Egg Crate.
The amount of loss depends on the narrowness of the cells, so a 30
degree Egg Crate will have smaller cells & less output than a 40 degree.
However, it's usefulness in the difficult task of controlling soft light is too big
an advantage to dismiss.