Gel Those Lights
When using lights during digital video production you are not just attempting to capture the subjects and objects as they appear to you right then. Instead, you are trying to actually alter the reality to create a digital video image that is both aesthetically attractive and in the service of the story and themes you are shooting for. To do this you can make choices about light temperature, light position, and light intensity. These are all fundamental video lighting changes you can make, but one of the most effective choices is to apply gels to the surface of the lights. This changes the overall color temperature of the light that is coming off and onto the surfaces, therefore changing the image entirely. Light gels can be used to make slight adjustments and major ones, all depending on your over all purpose in digital video imaging. When you are using them you can often encounter different issues that require you to do the same kind of troubleshooting that you would do in all of digital video production.
Video Lighting and Color Temperature
A very common thing for use of gels is to adjust to the color temperature of other light sources in the room, such as those from a fluorescent light or natural daylight coming through a window. Here you are going to want the control you get from an artificial light, but you want to maintain the same color temperature so that you can white balance out the objectionable color or color correct it appropriately. You may encounter issues when trying to get the color to match that of the other sources perfectly, and the white balance may not be getting out the colors correctly. To troubleshoot this with your lighting gels you should use a color meter to measure the color temperature of the light in the room. Then bring in your lights, set them up, and add the gels to them. Measure the color temperature and see where it is at. From there you can do a little trial and error until you get the color temperature of the light coming through the gels approximate to that of the room before the gelled lights were added.
An orange gel, called a CT, can often warm up an image entirely. You will often find that you want to give an afternoon orange glow over the entire scene without making it obvious that there is a light color coming in there. If you are seeing that the CT gel that you have applied to the light is adding too much orange this simply means that you are going to want to move down to a half or quarter CT, which is more appropriate for the situation. Full gels will often make the appearance of those gels known on the set, so only use them when it is acceptable to have noticeably colored light in your scene. The same is with blue gels that will mimic a cooler daylight instead of the orange Tungsten. This is going to be even more dramatic for any gels that are not orange or blue as they will always appear unnatural. If a full CT is too dramatic for your set up then a half strength green gel may have the same noticeable appearance.
If you want the gelled light to show up as altered in your scene, yet it is not, you have a few places to turn to. First, what happens often is that white balance is the last thing the camera operator and assistant camera person do. This is usually fine if you have even lighting all around and do not want to add any color. If you do you need to white balance first, and then add the colored gels. This will make sure that they actually alter the image themselves. You can also choose to trick the white balance by placing the opposite gel of the color you want the scene to be influenced by over the lens of the camera. For example, if you want to warm up the digital video image you can put a blue gel over the lens when you are doing the white balance. If the scene itself is simply not showing up the colored lights then you may not be focusing the light direction in an appropriate way. Bring the lights closer to the subject and see if you need to counter balance against the other non-gelled lights in the set up, especially in a four point lighting design.