Understanding Set Lighting and Color Temperature
The Kelvin Scale. Color Temperature. Tungsten, HMI, Fluorescent, LED lights. Here’s a full-spectrum look at the ins and outs of set lighting!
Cover image via Central Booking Service
Lighting a set is just as important as setting up the camera. Lighting affects the way a film looks, which is why the lighting department answers directly to the Director of Photography. With so many types and colors of light, it’s easy to become overwhelmed. Here is a look at all things light related.
The Kelvin Scale
Image via DownLights
Light is measured on the Kelvin scale. A kelvin (K) is a unit of measurement for temperature that is based on the absolute scale, which means it starts at zero and only goes up from there.
The lower the K, to more red the color. The easiest was to remember this is by candlelight. From 1000K-1900K, we are in the range of a lit match or candle flame. Fire = Red.
As we go higher on the Kelvin scale, we will progress to yellow lights, white light, and blue lights. Incandescent and Halogen lights are found around 2500K – 3000K. Direct sunlight has the equivalent of 4800K. Daylight is typically found around 5600K. A cloudy sky or cool white can be found between 6000K-7500K. A clear blue sky can be found at 10,000K.
You can see this progress in the color temperature chart above, and in the light bulb representation below.
Types of Lights
There are many types of lights. Here will we focus on the lights you most often see on a film set. Tungsten, HMI, Fluorescent, LED. Don’t forget that there’s another light available for free each day, the sun.
Image via ARRI
Tungsten lights are very similar to the light bulbs you may have in your home, just much more powerful. Tungsten bulbs produce an orange hue. The lamps require a lot of power and do get very hot, but they offer a higher color temperature than incandescent tungsten bulbs. Tungsten lights are dimmable, which allows you to adjust them as needed. They are usually used for lighting interiors. Add a blue gel to tungsten lights to create daylight.
Image via ARRI
Hydrargyrum Medium-Arc Iodide (HMI) lights are the most used type of light on set. HMI lights emit an ultraviolet light with a blue hue. To power up, HMI lights require an electrical ballast. The ballast ignites the metal-halide gas and mercury vapor mix in the bulb. Ballasts also limit the current to prevent flickering. HMI lamps are up to four times more powerful than traditional incandescent bulbs. There is a very loud noise when powering up HMI bulbs, so the lighting technician is required to shout “striking” to notify the cast and crew.
The age of an HMI bulb is very important. During its first few hours, a brand new bulb will have a color temperature up to 15,000K. These bulbs should be left on to reach the optimal range of 5600K, which is close to daylight. Bulbs should not be used past half their lifetime. The bulbs require more voltage and the color temperature will continue to decrease 1 kelvin every hour burnt, eventually risking serious damage if used too long.
HMI lights are rather expensive lights, but they are much more efficient. The bulbs can only be dimmed to 50%, but it causes the color temperature to rise to a stronger blue. If blown out or dropped, HMI bulbs will explode hot glass and mercury vapor. It’s very important to have a knowledgeable lighting technician on staff if using HMI.
Fluorescent (2700K – 6500K)
Image via ARRI
Fluorescent bulbs were notorious for flickering and having a very ugly orange-green hue. Recently, new bulbs and fixtures with ballasts have been developed. The new bulbs are flicker free and offer multiple color temperatures. They have a very soft light that is more efficient that an incandescent bulb, and can offer an output similar to HMI lights.
Depending on the mix of phosphors in the bulbs, the color temperature can range from tungsten up to natural daylight. Fluorescent bulbs are often packed into small fixtures, allowing them to be compact and light weight. They are also much cooler than any other bulb option.
LED (White: 3000K – 5600K)
Image via ARRI
Light Emitting Diodes (LED) have recently become much more prevalent on small sets. White LED lights are most popular, but LEDs are actually manufactured in every color. The diodes are designed to offer directional light. They are very efficient but are still limited in overall output, which is why they tend to only be used on small budget projects.
LED lights can only produce a single wavelength of light, so to create a white light requires a combination of red, green, and blue (RGB) LEDs. White can also be created with the combination of phosphors and an ultraviolet LED. Since the majority of LED lights use RGB, new “smart bulbs” have been developed to change color on command.
Image via Digital Trends
LED lights offer soft and even lighting. They are incredibly high efficient and can be battery powered. They can easily be dimmed and simply moved along the color spectrum. They have a long lifespan and will not explode.
Did this article help you understand the ins and outs of set lighting? Give us your lighting tips in the comments below!