I have been following the development of LED Fresnels with interest and so couldn’t wait to see what would be introduced at NAB this last weekend. I am happy to report that definite steps have been made in developing a production LED Fresnel light that combines the advantages of LED illumination (cool-burning, energy-efficient) with the versatility and control of traditional Fresnel fixtures. To reach this point, manufacturers of LED fixturess had to overcome a number of problems. The biggest problem of LED lights in the past was their poor color rendering (use this link - http://www.oscars.org/science-technology/council/projects/ssl/index.html - to the Academy of Motion Picture Arts & Sciences’ “Solid State Lighting Project” for details.) In addition to having poor CRIs, LED output and color decays with age, making their color rendering capability inconsistent at best.
A second problem inherent in LEDs that manufacturers have had to address is the relatively poor power quality generated by the Switch Mode Power Supplies (SMPSs) they use to power their lights on AC power. With Leading Power Factors around 0.54 (Litepanel 1x1s) and high harmonic distortion (THD upwards of 68.1%) the AC power supplies of LEDs have generally drawn a very distorted current that is significantly phase-shifted with respect to the sinusoidal voltage waveform. As such, the AC power supplies of LEDs have had an adverse effect on power quality similar to that of CFLs (use this link for more details.)
Finally, another drawback to LED fixtures until now is that the "light panel" design creates a light that is hard to control and falls off very rapidly. These characteristics have made LED light panels only suitable as Key sources in documentary interview set-ups where the Keys are typically positioned close to the interview subject. In that capacity LED light panels (with heavy diffusion) can generate a wonderful soft light that wraps around the interview subject without wilting them. However, in dramatic set lighting, where Key sources must be capable of throwing a distance, LED light panels have only limited applications as fill sources. The broad soft light they put out drops off too rapidly, and is too difficult to control, for them to be effective as a Key or Backlight source in dramatic set lighting. For LEDs to be widely used, manufacturers had overcome these shortcomings - their poor color rendering, poor power quality, and lack of versatility - to previous LED light designs. As I said at the outset, progress has been made on many of these fronts in the fixtures being introduced at NAB this year. Particularly in the case of the Litepanel Sola 6 Fresnel and the Arri L7 Fresnel.
The Litepanels Sola 6 LED Fresnel
While the Sola 6 Fresnel is definitely a step in the right direction in developing a production LED, far as I am concerned, Litepanels has not completely overcome all of the shortcomings outlined above with the Sola fixtures. Litepanels doesn’t give CRI ratings for the Sola Fresnels on their website, but when asked they say the CRI is in the 80s – which is still rather anemic compared to continuous spectrum light sources like quartz and HMI lights. The Power Factor of the Sola has been improved. But, at .85 it could stand further improvement (a Power Factor Corrected HMI has a Power Factor of .98 or near unity power.) They claim the 75W Sola 6 has the output equivalent to a 650W Tungsten, but comparing the photo-metrics published on their website to those of an Arri 650 Fresnel, the Arri has nearly three times the output of the Sola. And, while the Sola 6 has an impressive spot to flood range (10 to 70 degrees), spot/flood capability is not the only characteristic that makes a Fresnel light versatile. Of equal importance is the ability to render clearly defined shadows and cuts. The ability of Fresnels to render crisp shadows make them ideal for creating gobo effects like window or branch-a-loris patterns. The ability of Fresnels to render clearly defined cuts enables their light to be precisely cut to set pieces and talent. And, simply by adding one of a variety of diffusion material you can vary the softness of a Fresnel’s output. These are the characteristics of traditional Fresnels that make them extremely versatile, that the Sola “Fresnels” have not been able to emulate. Arri, on the other hand, may have finally engineered in their new 200W L7 LED Fresnel a fixture that combines the cool-burning, energy-efficient advantages of LED illumination with the controllable versatility of traditional Fresnel fixtures. Where I am out of space, I will have to pick up with my review of the new Arri L7 LEDs Fresnels in my nest post.
Guy Holt, Gaffer, ScreenLight & Grip, Lighting and Grip Rental and Sales in Boston.
A second problem inherent in LEDs that manufacturers have had to address is the relatively poor power quality generated by the Switch Mode Power Supplies (SMPSs) they use to power their lights on AC power. With Leading Power Factors around 0.54 (Litepanel 1x1s) and high harmonic distortion (THD upwards of 68.1%) the AC power supplies of LEDs have generally drawn a very distorted current that is significantly phase-shifted with respect to the sinusoidal voltage waveform. As such, the AC power supplies of LEDs have had an adverse effect on power quality similar to that of CFLs (use this link for more details.)
Finally, another drawback to LED fixtures until now is that the "light panel" design creates a light that is hard to control and falls off very rapidly. These characteristics have made LED light panels only suitable as Key sources in documentary interview set-ups where the Keys are typically positioned close to the interview subject. In that capacity LED light panels (with heavy diffusion) can generate a wonderful soft light that wraps around the interview subject without wilting them. However, in dramatic set lighting, where Key sources must be capable of throwing a distance, LED light panels have only limited applications as fill sources. The broad soft light they put out drops off too rapidly, and is too difficult to control, for them to be effective as a Key or Backlight source in dramatic set lighting. For LEDs to be widely used, manufacturers had overcome these shortcomings - their poor color rendering, poor power quality, and lack of versatility - to previous LED light designs. As I said at the outset, progress has been made on many of these fronts in the fixtures being introduced at NAB this year. Particularly in the case of the Litepanel Sola 6 Fresnel and the Arri L7 Fresnel.
The Litepanels Sola 6 LED Fresnel
While the Sola 6 Fresnel is definitely a step in the right direction in developing a production LED, far as I am concerned, Litepanels has not completely overcome all of the shortcomings outlined above with the Sola fixtures. Litepanels doesn’t give CRI ratings for the Sola Fresnels on their website, but when asked they say the CRI is in the 80s – which is still rather anemic compared to continuous spectrum light sources like quartz and HMI lights. The Power Factor of the Sola has been improved. But, at .85 it could stand further improvement (a Power Factor Corrected HMI has a Power Factor of .98 or near unity power.) They claim the 75W Sola 6 has the output equivalent to a 650W Tungsten, but comparing the photo-metrics published on their website to those of an Arri 650 Fresnel, the Arri has nearly three times the output of the Sola. And, while the Sola 6 has an impressive spot to flood range (10 to 70 degrees), spot/flood capability is not the only characteristic that makes a Fresnel light versatile. Of equal importance is the ability to render clearly defined shadows and cuts. The ability of Fresnels to render crisp shadows make them ideal for creating gobo effects like window or branch-a-loris patterns. The ability of Fresnels to render clearly defined cuts enables their light to be precisely cut to set pieces and talent. And, simply by adding one of a variety of diffusion material you can vary the softness of a Fresnel’s output. These are the characteristics of traditional Fresnels that make them extremely versatile, that the Sola “Fresnels” have not been able to emulate. Arri, on the other hand, may have finally engineered in their new 200W L7 LED Fresnel a fixture that combines the cool-burning, energy-efficient advantages of LED illumination with the controllable versatility of traditional Fresnel fixtures. Where I am out of space, I will have to pick up with my review of the new Arri L7 LEDs Fresnels in my nest post.
Guy Holt, Gaffer, ScreenLight & Grip, Lighting and Grip Rental and Sales in Boston.