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Lighting Essentials: Diffusion

Lighting Diffusion

One of the key elements of any lighting designer’s toolkit is diffusion. Diffusion takes on many different forms in the event world, primarily in lighting design as a means of spreading a beam of light out from a lighting fixture onto the intended subject. Also referred to as frost, diffusion in its simple form is a piece of plastic (a lighting gel) that fits in a gel holder in the front slot of a lighting fixture’s barrel. There are various versions of diffusion across different gel manufacturers (Rosco, Apollo, Lee, and Gam), and diffusion is used in everything from front light to back light, green screens and backdrops, film/photography set lighting, commercial lighting both interior and exterior, and everything in between.

Roscolux color diffusion

As a lighting fixture emits light on stage, the coverage and spread of the light depends on the fixture’s build, reflector, and lensing systems. A wash light might have a softer, wider spread of light, so it may be less likely to need diffusion. A theatrical spot fixture has a naturally hard edge, shutters, and built-in diffusion by moving the barrel along the focus track. Moving lights typically have a drop-in diffusion option to help blend and spread the beam of light, as well.

lighting diffusion


How do we incorporate diffusion with each show?

Front Wash Lighting

The key source of light that any audience member or camera sees on stage comes from the front of the stage. We use ellipsoidals (Lekos) as our primary workhorse fixture because ellipsoidals give us the ability to change degree barrels to cover the lighting needs based on the size of the stage and distance to the lighting fixtures. A short throw distance from fixture to stage gets a bigger lens degree, and a longer throw distance gets a smaller lens degree. These barrels, with proper spacing, allow us to control the size, brightness and evenness of each beam of light within each lighting system.

Front Wash Lighting

As we focus lights across a stage, part of our job is to properly blend the edges of our lights from one side of the stage to the other. We accomplish this using shutter cuts on the fixtures themselves, and then adding diffusion to blend the edges of each light together. With shutters and diffusion in play, any hard edges of light are blended, and only minor adjustments are needed as the cameras are white-balanced. A good front focus will leave the presenter evenly-lit as they travel across the stage, which will minimize the work for the camera shader during the run of the show. If the presenter looks to be walking in and out of shadows or bright spots on stage, then the front focus will need to be revisited and properly blended. While the human eye may not perceive as many differences in brightness across a stage focus, the camera tends to reveal any and all shortcomings in an LD’s focus.

We also use diffusion for any side lighting, back lighting, top lighting, and background lighting, but front lighting is the primary element to a stage focus.



Diffusion is for the presenter, too!

Another issue to consider in lighting a stage is the comfort level of the presenter or performer. The most standardized diffusion is Rosco 119, Light Hamburg Frost. The blend it creates works incredibly well for theatre and live events. In some instances, though, more shielding is required for the presenter. Often-times we find the comfort level of the presenter on stage is critical to a good production, and lighting can become a distraction to a good presentation if we are not careful. If lighting comes from a low angle, the presenters tend to find themselves in a deer-in-headlights situation – this requires us to run the lights at a lower level, and provide a heavier frost to shield the brightness of the light source. In low-clearance situations (television studios, film sets) where larger wash lights are being used to light the subject and background, heavier diffusion is needed to create a more natural lighting feel. If the presenter is within close range of the camera, and the lights are uncomfortably bright, the presenter may glow unnaturally on camera, and they will undoubtedly squint their eyes due to the brightness of the fixture. Heavy frost is a must!

lighting diffusion


Diffusion as Lighting Fixtures Continue to Modernize

As our industry continues to grow with improvements in LED stage fixtures, diffusion has continued to be a critical need. LED ellipsoidals and uplights rely on blending a flurry of diodes that are grouped together inside the fixture (as opposed to a traditional single-lamp as a source). These diodes present a challenge in that they don’t perfectly blend the way one would intend, and the diodes have more punch when you are the subject being illuminated. The need for presenter eye-shielding is very real with LED ellipsoidals. To combat this challenge, we go one step further in diffusing LED ellipsoidals by first placing a smaller piece of diffusion in the gobo slot of the unit. This serves to blend the LED diodes prior to the light travelling through the lens of the fixture, and we place Light Hamburg Frost in the gel slot to allow for smooth blending. LED uplights typically have a frosted lens of a gel slot to blend the colors into the scenery that is being illuminated, as well.


Diffusion: A Conclusion

Stage lighting is key in helping our clients communicate with their audience. Our goal in lighting is to convey the client’s message clearly, effectively, and without distraction. The primary building blocks to reach these goals begin with an attentive designer, lights to shine on stage, and, of course, diffusion.



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