Lighting is one of the critical factors impact the final result of film or video making. We emphasize it again and again when doing film production.
For filmmaking, what we are familiar with the important parameter of the film and video lighting should be Color Rendering Index (CRI). While apart from that, we should know more about other references to distinguish the lights’ quality for film and video lighting, such as Correlated Color Temperature, Color Temperature Tolerance，Color Temperature Consistency，Color Accuracy, DUV, etc.
In this article, the relationship between DUV and film and video production.
Before we start the film or video production, we need to adjust our camera to match the light sources’ white color in order to get the best white balance performance. However, when the light source is not good enough for your cameras, such as inaccurate color temperature (CCT), low CRI value or incorrect colors, your final footage will occur significant color shift which is called abnormal tint.
Film production lighting and the theory of BBL (Black Body Locus)
In High CRI LED Lighting, each LED light has its unique CIE 1931 xy coordinate. If looking at the black body locus (BBL), we will find the horizontal difference and vertical difference of xy coordinate, which is represents CCT difference and DUV difference.
In general, what the perfect light we need for film and video production lighting is pure white light. And indeed, for warm white light tungsten, because the tungsten light source contains more red part radiation, therefore, the final white light output would be more like orange hue. Likewise, for daylight light source, because it has more blue part radiation, its white light output would be more like blue hue. This tint-diversity phenomenon is because of the difference of Correlated Color Temperature (CCT), while they are still pure white light as long as their xy coordinates stand on the black body locus (BBL).
Know more about white balance and CCT.
However, apart from these natural blue’ish and orange’ish light output, filmmakers or gaffers will also find the sense of green’ish and magenta’ish of the light emits from film and video lamps. Unlike CCT difference, this tint-diversity phenomenon is abnormal and unacceptable for film and video lighting. It is due to the difference of DUV and will influence the camera performance of white balance and consequently impact the footage effect.
Know more about white balance and DUV.
How to distinguish the pure white light lamps before purchasing?
So, in order to find the correct pure white light source for film and video light, we should first know some things as follow.
- What is DUV？
- What does DUV difference stand for?
- What is good DUV value to ensure color accuracy?
What is DUV？
Duv is the short name of “Delta u,v”, which is defined in ANSI C78.377. As we mentioned before, every lamp has its unique CIE 1931 xy coordinate. And it describes the distance from the Black Body Locus (BBL) vertically. For film and video production lighting, it describes the extent of green’ish and magenta’ish.
MM’s also provides the software for Duv calculation, therefore, you are able to judge if your lamp is emitting pure white light, or if it is green’ish or magenta’ish.
What does DUV difference stand for?
When we looking for some tint sensitive lighting applications, such as film and video lighting, color accuracy is very important. While we are not able to judge if our lamps are pure white light source or not, if we only have the parameter of CCT. Therefore, Duv value becomes crucial for selecting correct color light sources.
In the picture below, you will find that different CCT has its unique line, which is called iso-CCT line. The xy coordinates on same line has the same color temperature.
Let’s look at color temperature tungsten, 3200K or 3000K, as you can see in the picture above, the iso-CCT line extend downward from black body locus to pink or magenta area.
In other words, if we have a lamp with 3200K color temperature, its xy coordinate can be any points on 3200K iso-CCT line even in the pink/magenta area. The distance of the point away from black body locus is named Duv value. What if this value is high, for example, Duv = +0.03 or Duv = -0.03, the xy coordinate of this lamp will be far away from black body locus, which means awful color accuracy.
What is good DUV value to ensure color accuracy?
ANSI and EnergyStar institution announced the recommendation of Duv value in the range of +0.006 and -0.006 is good light. While for some special lighting applications require strict color accuracy, we recommend the good Duv value should in the range of +0.003 and -0.003.