Ever wondered why I’m so fussy about ‘clean’ lighting with my coloured gelled photography? Well it’s because failing to produce cleanly lit shots with gels, simultaneously produces horrendous looking shots with gels.

When I refer to clean lighting I’m referring to the fact that I like to keep all of my lights in my scene exactly where they’re supposed to be. If I have a background light then I have it lighting the background and nothing else, when I have a hair light, I have it lighting the hair and nothing else and so on. This might seem fairly obvious but when you’re using white-light and large modifiers like softboxes, the lighting is going everywhere whether you like it or not. We simply can’t get away with being that sloppy with coloured gels.

So why do I insist on clean lighting with gels? Well it’s because when two coloured lights mix, they don’t mix like paint, they mix like light does.

Not only don’t they mix like we think they should but they start to produce an awful looking side-effect we call ‘colour banding’. I’ll go into what colour banding is and what that looks like in more detail later on but first off let’s take a look at what I’m referring to when I say ‘mixing’ light versus mixing paint.

The physical mixing of colours is refereed to via a ‘subtractive’ colour wheel and this is used in reference to mixing colours like paint. Light hits the paint on a canvas and is reflected back into our eyes and we see the colour that way. This is the regular colour wheel we’re all used to seeing and using.

For mixing light however, we use the term ‘additive’ colours and this is specifically referring to how light mixes from transmissive devices like T.V.s, smartphones and so on. No light is reflected off any surface like a canvas and the colour is mixed as we see it directly on the screen.

Take a look at the diagram below to see just how differently colours mix with paint compared to light.

How do we create coloured light?

So before we get ahead of ourselves, what is coloured light? The short-form of this is that white light is actually made up of a full spectrum of colours. Basically that means that when you shine multiple coloured lights on top of one another, you’re actually just getting closer and closer to a white light with no colour at all. But don’t worry you’re not alone if think this is weird because we’ve all spent our entire early school years learning that mixing colours and paint is very different to this. We’ve been told that mixing colours like blue and yellow will result in green and that if we mix red and yellow we’ll get orange and so on. You can literally forget all of that entirely when it comes to photography and mixing coloured lighting.

The diagram below illustrates that white light is in fact a completes rainbow (spectrum) of colour.

So how does this relate to us as photographers? Well take a look at the diagram above to get an idea of what coloured gels actually do to our light once it has left the flash. White light leaves the flash and travels into the gel. Like we mentioned before, white light is actually a complete rainbow (spectrum) of colour so when it hits our red gel, the gel isn’t actually turning the light red but instead it’s filtering out all the other colours of the spectrum leaving only red behind.

So now imagine the same thing happening with a blue gel and a green gel alongside this too, with their powers combined (they produce Captain Planet – if you get that reference you’re officially old ;) ) they create white light once again on the resulting surface.

When RED, GREEN & BLUE light are combined they produce white light.

The Two Colour Wheels

Yes, that’s right, you heard me correctly earlier on, there are in fact two colour wheels and we need to understand how they both work, how they relate to one another and what’s important for us as photographers before we can continue.

I spoke about ‘additive’ colours and ‘subtractive’ colours before, now I’d like to try and explain these in terms that relate to us as photographers so from now on I’ll be referencing ‘subtractive’ colours as the painters colour wheel and ‘additive’ as the lighting colour wheel as we continue.

First off let’s take a look at how the two colour wheels differ visually.

They’re certainly very similar but there are a few key differences in the way the colours are laid out to illustrate how colour is mixed between them.

First we should clarify what the primary colours are in both of these colour wheels. If you’re not sure what defines a ‘primary’ colour then it’s the core set of three colours that all other colours are derived from. In the painters wheel it’s Red, Yellow & Blue and in the lighting colour wheel its Red, Green & Blue (RGB).

Now that we know what the primary colours are for both the painters colour wheel and the lighting colour wheel we can start to take a look at how these primary colours mix to create other colours. As we start to mix these colours we can now see why these colour wheels are laid out the way they are. Take a look at the two sets of colour wheels below to see what I mean.

You should see that secondary colours are simply the colours that sit between the primary colours on each of the wheels. So although both colour wheels seemed to have a red and a blue in common for their primaries, the secondary colours are clearly quite different.

There is a very reasonable scientific reason for why we have two colour wheels and how reflected light and transmissive light of subtractive colours and additive colours respectively vibrate at different wavelengths to create varying colour combinations… but this article is long enough already. My aim is to create an article specifically targeted at photographers and what we NEED to know but if you’re interested in the deeper-dive physics of this topic then I recommend this linked article for some light bedtime reading (see what I did there) on Light Absorption, Reflection and Transmission. Enjoy :)

Complimentary Colours

So now let’s take the principles we’ve learned about what ‘white’ light actually is and apply a little colour theory to it. In art we have something called colour theory, this is the principle that certain colour combinations are more favourable and resonate well with us as people over other colour combinations. One of the most popular colour theories is the one we refer to as ‘complimentary colours’ and this is one we’ll be exploring a little deeper with coloured light here.

If you have a colour wheel then complimentary colours are very easy to understand as a complimentary colour is simply any colour that is opposite one another on the colour wheel.

Take a look at the colour wheels above and you’ll see the examples of complimentary colours that I’ve pointed out. These three colour combinations are certainly the most popular; red & green, purple & yellow and orange & blue but is there a reason for that?

Well the reason these complimentary colour combos are so popular is because they each contain a primary colour and a secondary colour. If you’re a bit rusty on your primaries and secondaries then take a look at my handy image below to refresh your memory.

Now let’s take a look at how those secondary colours are created by mixing two primary colours.

Blue & Yellow = Green

Yellow & Red = Orange

Red & Blue = Violet

So it stands to reason then that colours that are essentially derivatives of their primary brothers actually become their complimentary counterpart.

For example; yellow and purple are complimentary colours, the other two primaries that aren’t yellow are red and blue, mix those together and you get purple which is your complimentary colour to yellow.

JEEZ JAKE! I normally only come here for the pretty pictures of ladies covered in oil and coloured lighting!!! This is a bit much!

Yes, I do apologise this is a bit of a headache but you really don’t need to know the math behind colour theory to be good with it but it certainly can be nice to know how it all ties together. Here’s a quick list of the complimentary colours and how they relate to their primaries.

So although you don’t need to fully understand the reasoning behind how certain complimentary colours are made, you do need to know how important they are.

Everything from room decor to corporate branding to the clothes we choose to wear to the packaging we’re drawn too on the shelves undergo colour theory before they’re released.

I cannot overstate how powerful colour is to us in our everyday lives so it stands to reason that colour theory is incredibly important too.

The biggest distinction to make so far about colour theory is that it uses the painters wheel to figure out harmonies in colour. Do not use the the lighting colour wheel to work out what colours work well together, that is purely used to show you how certain coloured lights will mix to generate other coloured lights.

Mixing Complimentary Colours with Coloured Paint

In the previous section I explained the importance of complimentary colours and how powerful the colour theory behind them actually is. Before we talk about using complimentary colours in lighting though I just wanted to quickly show you what happens when we mix complimentary colours with paint.

I doubt the resulting images below are of any surprise to anybody. Paint mixes the same way physical colours always have done and the resulting colours are the same now as it was when we were crushing up beetle shells and mixing it with fern roots. The important thing here is how different this is to mixing complimentary colours in lighting.

Yes, when I use the term brown to describe the resulting colours above I’m generalising greatly as there are many different versions of brown but let me explain how the colour theory of paint works when it comes to mixing colours.

When you mix primary colours (red/yellow/blue) you get the secondary colors (orange/green/purple). When you mix the primary colors with the secondary colours or use different amounts of primary colors, like if you have more yellow than blue, you get all the other shades in the color wheel like yellow-green, blue-green, red-orange, yellow-orange, blue-purple, red-purple, and so on.

So when you mix two complementary colors like purple and yellow you simply get a shade of ‘brown’. The brown isn’t important but what is important is how we get a very different result when we mix complimentary colours in lighting.

Mixing Complimentary Coloured Light

Okay so now let’s take the test to our photography world and see how colours mix when using light compared to paint. First off, let’s take a look and see what happens when we mix the lighting primary colours of Red, Green and Blue. This will give us a baseline of how light mixes compared to paint and it will also show us why the RGB colour wheel is laid out the way it is to create its secondary colours of Magenta, Yellow and Cyan.

This test was fairly simple thankfully and all I did was attach coloured gels to the ends of two gridded strobes, fired them against a white wall and took shots of the colours separated and another couple of shots of the colours mixed.

So the results above speak for themselves and although I was aware of the principle of mixing coloured light before I did this test, I was still pretty surprised how well these coloured lights actually mixed on a wall. Remember, the lighting colour wheel is based on mixing transmissive colours, colours that mix as they are emitted from a screen not shone onto a surface.

The next stage was to test how the complimentary coloured lights mixed. The results were very different and in all honestly, pretty surprising.

What’s interesting about these results is why it is so, so important for us to employ clean lighting when using coloured gels. Thankfully, red and green are two of our primary colours on the lighting colour wheel so mixing those two coloured lights produced the expected results, of yellow but it’s when we mixed the other two complimentary colour combinations that it got interesting.

Mixing both violet & yellow and orange & blue actually produces grey.

It’s probably better to say that they actually cancel each other out but essentially mixing these two complimentary coloured lights together removes their colour leaving a dull white colour in its place.

Colour Banding or Bad Lighting

So finally, you made it this far and we can at last get into this ‘colour-banding’ problem that I’m sure we’ve all faced at some point.

So what is colour banding? Well colour banding is that odd ‘stepping’ of colour that can be produced in very saturated images. Colour banding is when colour doesn’t smoothly transition from one colour to another in our digital images. In the image below you should see that the colour on the models arm goes from orange to a grey colour then to blue and this look is often refereed to (sometimes mistakenly) as colour banding.

Now technically speaking this example isn’t strictly colour banding but for the same of argument we’re going discuss what causes this effect and how to avoid it.

This infuriatingly ugly effect is a huge problem with coloured gelled lighting and for years I thought it was simply crappy digital cameras not having the power to render all the colours I wanted, and although this certainly plays a part, it would seem it’s not all the cameras fault.

The above raw image clearly illustrates what looks like colour banding but in actuality it’s not the cameras fault but in fact it’s messy lighting. What is happening here is two complimentary colours are meeting on the skin and when they do, they go grey as they cancel each other out. Look closely at the circled section above and you’ll see that the colour on the arm goes from blue to grey to orange; not a pretty look. Remember what happened in our lighting test earlier on when we mixed complimentary coloured lighting? Look familiar?

So how can we avoid this? Well the simple answer is to firstly be very aware of what happens when you mix certain coloured lights together in a scene. The biggest offenders (and likely the ones you’ll be mixing the most) are the complimentary colours. Thankfully red and green only produce yellow which although unlikely to be a good thing is still better than grey and of course the biggest culprits being the mixing of orange & blue plus the purple & yellow creating grey. This gelled lighting phenomenon is definitely something that you want to avoid at all costs in my opinion and you can do that with proper light control like we see below.

All of the images above show the heavy use of the complimentary colours orange and blue but you should see that I’ve avoided the dreaded grey colour overlap that can occur by combining these lights by keeping the lighting clean and never spilling the two colours onto one another.

Now I understand that this is a LOT easier said than done and actually keeping the lighting separate is the topic for another article but I hope you can see how important clean lighting actually is now.

Closing comments and conclusions

Firstly, thank you if you’ve made it this far in the article, I’m not known for my short, snappy social media posts or articles and this monster of a piece is no different. But I do feel that everything being said here is relevant and although I debated splitting this up and getting multiple posts out of it, I really think everything here needs to be seen together to fully understand what is going on.

Although I didn’t want to complicate this any further, I will just add that we as photographers actually operate between the two colour wheels. Don’t panic, what you’ve read so far is relevant but we as artists who use light as our medium fall between the two colour wheels because the lighting colour wheel is for transmissive RGB displays only. Yes we use light but we shine that light onto an object and then photograph that reflected light and reflected light is what painters use to mix colour. I know that is a bit of a mind-bender but really all you need to know is that light mixes like it does with RGB but bear in mind that requires a white surface to be the subject for it remain relatively accurate. Chances are you’re not photographing coloured gels on white walls so caution is required when making assumptions about the mixing of colour on another surface that has its own colour like skin. Like I said, I didn’t want to over complicate something that was already fairly complicated but I wanted to highlight that point to any of you who may have been wondering about it.

Points to remember

1. Use the painters (subtractive) wheel for colour theory. For example, use the painters wheel for working out complimentary colours.
2. Use the lighting (additive) wheel to work out what coloured lights to mix, or what will happen if you do mix certain coloured lights together.
3. The more paints you mix together, the darker the colour will get. The more lights you mix together, the lighter the colour will get.
4. Complimentary colours are always opposite one another on the painters wheel. For example; orange and blue.
5. Mixing two of the three primary colours will result in a secondary colour for both the painters and the lighting colour wheels.
6. Mixing certain complimentary coloured lights will result in grey. For example; orange and blue, purple and yellow.
7. Always try to keep you coloured lights separate on whatever it is that you’re photographing. Failure to do so will result in an ugly looking colour banding effect.

For reference, print out or save these ‘cheat-sheets’ below on how colour theory works.

For more of these cheat-sheets, head over to my Quick-Tips page that has loads more of them on all kinds of photographic topics.

I know this was a monster-brain-melting-article but I’ve seen very little on this topic that is specifically targeted at us photographers so I hope it helps at least one person understand more clearly what’s going when mixing coloured gels.

As always, thank you and if you have any questions or anything to add, feel free to keep it to yourself…….sorry I mean post it in the comments below ;)

About the Author

Jake Hicks is an editorial and fashion photographer who specializes in keeping the skill in the camera, not just on the screen. For more of his work and tutorials, check out his website. Don’t forget to like his Facebook page, follow him on Flickr, Instagram and Twitter, and subscribe to his YouTube channel. This article was also published here and shared with permission.