Quality of Lights (CRI)
Updated: Nov 24, 2019
Light Characteristics include, lumens or footcandles (brightness), spread (fresnel, par, flood light) and Color temperature. Since the inclusion of LED lights in the industry, another attribute is being more considered, and it is the Color Rendition Index.
Color Rendering Index (CRI) is the measurement used to describe a light's ability to render colors accurately. The higher the CRI, the better the quality. Tungsten lights, fire, and the sun, have all the colors in their spectrum (100 CRI). To accurately show the true color of an object, the light needs to have that certain color to reflect it into our eyes accurately. Lights with low CRI lights may not contain the exact color of an object, thus the object's color would only reflect the spectrum of lights that are available. In this case the object won't be as color accurate as it would be under a full spectrum light. The lowel tiffen link goes into more detail of what CRI is and its science.
Back before LED fixtures, CRI was a rare problem since Tungsten (100 CRI), Carbon Arc (100 CRI) and HMI (96 CRI) units have almost all the colors in the visible spectrum. The distinction between them is the bias to the warmer or the bluer side of the color spectrum. With the advancement of technology, LED lights are slowly coming into the scene with its low heat, and very low power intake. These advantage have their costs however; mostly lower output in comparison to tungsten and HMI units, and color rendition flaws. Some LEDs today are becoming more powerful and have better color rendition.
Light Emitting Diodes (LED), need a more accurate measurement than CRI since CRI only accounts for eight colors that have good representation of the color spectrum. LED lights use many different colored diodes to create any light in the color spectrum. The video at the bottom of the sekonic page goes into detail of what is a good measurement for LED fixtures.
With Extended CRI, more colors are added in the measurement that can accurately distinguish the color quality of the light. The more important measurement is r9, since LEDs have trouble to accurately portray the color red. This measurement is used in Sekonic's high end color meter. Indiecinemaacademy has one of the best database for LED lights. They contain the most up to date LEDs and their color science.
Why is it important in film?
Skintones. One of the most important aspect of the light is its ability to create accurate skin tones. Professional grade films and videos puts skin tones in its top importance. The lights make the subject look good. It would be a shame to ruin a talented and beautiful actor's skin tone because of low quality lights. Most LEDs have green tint which makes skin tones look sick. The Nofilmschool link at the bottom, shows the quality of skin tones in different light settings.
Arri's skypanel line up is the most popular LED lights in the movie industry. With their 90 + CRI, strong output (compared to other LEDs), and low power draw (450w nominal) they are slowly becoming the LED workhorse of the industry. With LED's capability to change Hue and saturation, all the colors can be replicated. Skypanel also has various effects (police sirens, paparazzi, color chase), green/magenta shift, dmx capability, and gel library (Rosco and Lee filters) which makes them the most versatile lights. Some of the other LEDs lights that are becoming more popular are the tube LEDs (Asteras, Quasars, Colts, Digital Sputnik), Litemats/LiteTiles, and LED source 4 theatrical lights.
Nofilmschool's youtube video shows a good comparison of lights and their quality in front of a camera. https://www.youtube.com/watch?v=LMbRjiBqZyg&t=285s&list=LLLVVHg60TinDaRxxKBOyroQ&index=12
The video even compares the LED lights to natural daylight and Tungsten lights.
One disadvantage that keeps the skypanel from being the only lights needed on a film set, is their spread and their output. The skypanel line-up is a flood light, meaning its not meant to create strong shafts of light and despite being bright, it doesn't come close to the stronger HMI and Tungsten output. Fresnel tungsten and HMI Pars are used for big output and long throws. There are no notable fresnel LED lights that have been as popular as the Skypanel. Mole has some high output Fresnel but the demand for it isn't there. I believe it's the color science that keeps it from being in demand.
The Digital Sputnik Anomaly
Digital Sputnik's DS series' CRI is lower than 50. This is something I've never figured out since there is not that many literature on it. An article from ASC magazine interviewed the head of Sales for Digital Sputnik about the color science of their product.
Knowing that the light was used in Rogue One and other big Hollywood films, I'm starting to question the accuracy of the CRI measurement. Could it be that digital sputnik found a color science that tailors very well to digital camera with their understanding of the digital debayering? The skin tones do look good in video but I need to see it in comparison to Daylight and other LED lights, and through other consumer reviews. It's always been through digital sputinik where I gathered this information. Once I find a better source and testings with the Digitial sputnik, then I will look into a more accurate measure of color quality of a light. But for now, I will stick to Extended CRI as a main measurement since it has been shown to make good representation of the color quality of a light.
Will tungsten and HMI lights eventually be replaced by LED lights with its improving technology? I think so, BUT not in the near future. Tungsten and HMI have output that cannot be matched so far by LED fixtures. These old school lights have been such a big part of the film industry that its workflow in the lighting department have been solidified. With color quality that is not matched so far by LED, quartz halogen lights and medium arc iodine will stay maybe for another 30 to 50 years. There is a reason why big power distribution, big generators, and a huge cost of lighting rental for tungsten and HMI lights are still an industry standard for shows and films. Other technology can come into the film industry as well with Plasma lights. There might be other technology that we don't know yet.
But for now, I observe RGBW LED lights mostly used for music videos, corporate and commercials, while tungsten and HMI are still the workhorse of the film industry.
Level Nine Productions