For those who have never been to a farm or dairy, Egg Crates are named after the cardboard grid that farmers would place in a box to keep eggs separate from each other as they were transported to market. On lighting fixtures, they help to control the spill of a soft source by limiting where it can go. In the real world, you may have seen them used in traffic intersections on "Walk" & "Don't Walk" lights, keeping their lighted messages visible only to those in the crosswalks.
Trimming the Beam Angle with Egg Crates
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No Egg Crate (90 degree beam angle)
50 degree Egg Crate = 50 degree beam angle
40 degree Egg Crate = 40 degree beam angle
30 degree Egg Crate = 30 degree beam angle
| 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.
Rifa-44, with 50 degree Egg Crate