Open Frame

Technical Details

Open frames utilize Fresnel lenses with diameters ranging from 150mm to 300mm or parabolic reflectors without additional diffusion discs. The light distribution follows a cosine-shaped characteristic, providing illuminance levels of 800-3200 Lux at a distance of 3 meters (2kW Tungsten). Modern open-frame LED panels achieve CRI values exceeding 95 and color temperatures between 2700K-6500K. The diffusion occurs without directional control, allowing the light to spread evenly over 180-degree areas.

History & Development

In 1943, the Mole-Richardson company introduced the first standardized "Open Face" spotlight for Hollywood productions. This development arose from the need to illuminate large studio areas cost-effectively, without complex diffusion setups. In the 1960s, open frames became established as the standard for exterior shots and available light situations. Digital cinema cameras from 2005 onwards amplified this trend through higher light sensitivities, making open frames usable even with lower power outputs.

Practical Use in Film

Terrence Malick used open LED panels in "The Revenant" (2015) for natural daylight simulation in interiors. This technique is particularly suitable for group scenes where multiple people need to be illuminated evenly without complex shadow geometries. Documentary filmmakers prefer open frames due to their rapid deployment and low weight. Disadvantages become apparent when precise light shaping is required or when spill light falls into unwanted areas of the frame.

Comparison & Alternatives

In contrast to Fresnels with barndoors, the open frame does not allow for selective shading of individual image areas. Softboxes produce softer light but require 2-3 times more setup time. LED mats are increasingly replacing traditional open tungsten spotlights due to lower power consumption (90% less) and precise color control. Kino Flo tubes offer similar uniformity with less point source radiation.