The following lesson was created by Vimeo for its Vimeo Video School . It’s used here with permission. Look for a new lesson each week.
Hey there budding videographer, let’s talks about gels and diffusion. No, I’m not referring to the hair grooming habits of the guys from the Jersey Shore  series, but rather using simple pieces of plastic to filter your lighting so your video looks better.
Gels are pieces of colored plastic that allow light to pass through, but change the color tone of the light itself. Diffusion, while similar, has a different purpose, reducing harsh shadows by softening the light. By increasing the surface area over which your light is emitted, you get less of a headlight effect, and that’s generally a good thing. Strong, harsh lighting can be used for dramatic effects, but in most scenarios you’ll want to soften it up to make your scene look more natural. Now, let’s jump-start this discussion with an overview by Scott Spears from Framelines TV .
Scott goes over some important points, so let’s review them a bit. First, getting your color temperature is really important, as we’ve mentioned in previous lessons on white balance . One of the ways gels can help is if if you’re shooting a scene with a mixture indoor and outdoor lighting. With colored gels you can match to indoor or outdoor lighting. Remember blue gels will give a cool look while orange gels will warm up your light, match accordingly!
Gels are also handy when you want to simulate lighting conditions. For example with enough warm colored gels (primarily oranges and reds), you can give your scene a sunset/sunrise look or alternatively with enough blue gels and a bit of underexposure you simulate moonlight. Also note, sometimes green gels are used to convey a feeling of unease or sickness. Additionally you can also use neutral density gels, which won’t change the color of the light but will help take down the light intensity, which is helpful in small quarters with bright lights. For more about neutral density, check out this lesson .
Now let’s go over some general ideas about diffusion. Why diffuse it all? Well light is great and all but you need to soften it or you end up with harsh distracting shadows and reflections. Like we discussed in our paper lantern lighting lesson, strong light is good but it needs to be tempered. By spreading that light over a greater surface area you soften up the quality of the light so actors and objects will appear more natural. Diffusion comes in different thicknesses which will make the light correspondingly softer or stronger.
Well now you know, the next time your scene lighting needs a little something, consider changing up the color and/or light intensity with some gels or diffusion.