Monday, April 28, 2008

Lighting 102: 6.1 - Gelling for Fluorescent

On their face, gels are a pretty simple concept. You stick a colored piece of plastic in front of your flash and it alters the color of the light accordingly. But so much is possible from just this simple trick.

In this, the first of a four-part section on using gels, we'll be looking at their most common use -- converting the color of your flash's light to the color of the ambient light in which you are shooting. This is called color balancing.

We first visited the idea of color balancing in Lighting 101 where the two most important gels were discussed. The "window green," (or "plus green") gel converts the light from a flash to nominally match that of a fluorescent light.

A "CTO" gel similarly converts your flash's light to match the light from an incandescent (i.e., tungsten) bulb. But for today, we'll be talking about just the little green gel. It's certainly complicated enough to merit its own post, as you'll soon see.

While the fluorescent conversion used to be a simple process, this is no longer the case. But for the sake of discussion, let's assume that it still is. At least for the moment.

Traditional fluorescent light is green. About 30 color correction (CC) units of green, to be exact. By placing a 30cc window green gel on our flash, you make the flash's light match that of a traditional fluorescent environment.

If our ambient is green, and your flash is green, you're okay. Because you can correct for all of this similarly green light by setting your camera on the fluorescent light balance, and all is white again. This is because the FL white balance setting just shifts everything over 33 units of magenta. This is what balances out the green.

Take, for example, this shot I made a couple of weeks ago at Western Kentucky University, while teaching the PJ students there.


(Sorry, Jeanie. You were my most recent example...)

This is a fluorescent-lit studio. In this shot I lit Jeanie with an SB-800 in an umbrella and the flash was gelled with a window green gel. My shutter speed was opened up to let the background of the photo burn in to make a decent exposure.

But in addition, the green gel, combined with the camera on fluorescent setting, brings the colors up pretty close to correct. None of that sickly-green cast that happens when you forget to gel your flash and the fluorescents just come in the ugly green way they really look.

Pretty simple technique, right?

But in practice, there are two little gremlins that usually come into play. First, rooms can often have a mix of fluorescent and daylight. Maybe even a little tungsten thrown in for good measure.

In addition to that, fluorescent lights are now all over the map, color-wise. In reality, they can now actually be warmer than tungsten.

Let's take these problems one-by one.

First, on the multi light sources, sorry to say that you have to choose a source color and go with it. But this can be better than it sounds. My first trick, if there is a lot of daylight bouncing around in a fluorescent room, is to ask if I can turn off the overhead lights while I shoot.

If the daylight is enough to cause light balancing issues, there is usually more than enough to work by with the fluorescents turned off. Then you do not balance at all -- just shoot in the daylight with normal flash.

If that solution is not available, I will close the blinds or drapes to minimize the encroaching daylight. (This daylight comes through as magenta when you are set on fluorescent white balance.) One other thing you can do to help are to work on the opposite side of the room as the windows, to minimize the daylight contamination.

If you have a mix of fluorescent, daylight and tungsten, do everything you can to lose the fluorescent light. Then shoot on daylight with no color correction gel on your flash. The daylight and tungsten will mix a lot prettier than any green/other combo will.

(And if all else fails, hope it runs in black and white...)
____________


And as we said earlier, fluorescents are no longer just 30cc's of green. And for us photogs, that really sucks.

There is no good solution here. The important thing is that you have to be able to counteract your conversion gel with a white balance camera setting. That is to say that, even if your fluorescent light is not a perfect green, you pretty much have to live with the difference. Just green your flash and neutralize it (the flash) with the FL white balance setting. Sometimes the ambient will go a little weird. But it is better than not gelling at all.

For those super warm fluorescents, the ones close to tungsten, I will usually just treat them as tungstens. I'll CTO the flash, and set the white balance on the camera to tungsten. Again, not perfect. But better than nothing. And the flash-lit part will look good.

How can you tell where the fluorescents are, color-wise? The easiest was is to shoot an ambient-only shot and chimp your screen. If it looks more green, gel and balance for fluorescent. If it looks more orange, treat it as a tungsten. This is also a good approach for working in vapor-based light (sodium, mercury, etc.).

Your flash-lit subject (usually the most important part of your frame) will be okay. The ambient burn-in part may be a little off. But that's the price we now have to pay for having 57 varieties of fluorescent bulb colors.

And as for dealing with tungsten lights, we'll be hitting that in the next installment of Lighting 102.


NEXT: L102 6.2 - Geling for Tungsten


__________

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38 Comments:

Anonymous Anonymous said...

If you have a mixture of fluorescent and tungsten lighting in a room, could you not throw both of those gels on the flash to try and mimic the light mixture going on in that room?

April 28, 2008 12:40 AM  
Blogger Vincent said...

I carry an expodisc that really does a great job of getting a good custom WB. THe same can be said for a white sheet of paper that fills the frame. Either photograph it or through it. Making sure your histogram reads the exposure almost dead center. I dunno if its perfect, but it works for me.

April 28, 2008 12:46 AM  
Anonymous Anonymous said...

I was never satisfied with the results using a green gel under fluorescent. Testing with a Whibal card and RAW adjustment revealed that most fluorescents are not only a bit green, but also have a color temp about halfway between daylight and tungsten.

After some experimentation, I came up with a set of gels I can live with for use with most fluorescents. From the Rosco swatchbook, I use these two gels, stacked:
#3315 Tough 1/2 Plusgreen
#3408 Roscosun 1/2 CTO

Curtis

April 28, 2008 1:15 AM  
Anonymous Anonymous said...

I'm so glad you brought this up. after reading 101 I went and got some green and cto gels. but the green are almost useless for me. all the compact florescent bulbs in my home are all very warm and I gel with a cto instead. nowdays it seems only the 48" bulbs are green and even some of those are not green.

April 28, 2008 1:50 AM  
Anonymous lenny said...

I agree with the opinion of just using a WhiBal card (or similar) to white balance instead of filters. It seems the color correcting gels are for film. Anyone know if the gels would actually be a better solution over a whibal or similar device when shooting digital?

April 28, 2008 2:06 AM  
Blogger Rockhopper said...

The D2x comes with a device fitted that measures ambient colour temperture. However recently doing a restaurant shoot the colour balnce was everywhere. I have tried the CTO and green gels they do help on a set up shot. Unfortunately the client was not willing to pause food preparation so reportage shooting style had to be used. They only way to get round it was to walk round and colour balance check the whole shooting area. I had a little white sticker with a rough map and a code. I walk into that area I change the colour balance setting by looking at the code on the back of the camera. You could do a quick shot and do it but you lose the moment however.

Just a little tip. Hope it helps

April 28, 2008 2:19 AM  
Blogger JK said...

I live in Indonesia where such gel is scarce if not available here at local stores. Is there any alternative yet cheap material we can use in place of rosco gel? I tried a number of plastic colored material cut out of plastic book binder (so called) with no luck. Thanks for advice.

Jusuf

April 28, 2008 2:45 AM  
Anonymous Anonymous said...

Well from what I know of fluorescents its not only about the color temperature matching and more about the loss of huge chunks of the spectrum as well as a large spike in the green. Fluorescents have CRI (color rendering index) which basically tells you how complete of a spectrum the bulb produces. http://en.wikipedia.org/wiki/Color-rendering_index
I love how more and more people and businesses are switching to the higher CRI bulbs the issue i have run into is locations being half one high CRI and half the good ole crappy fluorescent.

Max H.

April 28, 2008 2:47 AM  
Anonymous Blaise said...

Hi,

Excellent post as usual.

I would like more explanations on "seeing" the light. ie - walking into a room an knowing which type of light this is. You've touched on this in your article but it's still not clear enough to me.

When I take photos on Auto-white balance indoors I generally get orange - yellow pictures. I have yet to see a green one. Does that mean that I need to almost always use a CTO gel and that as you mention the fluo traditional color is out?

Alternatively could I simply take a first photo in AWB and then decide on the gel depending on which color I get?

thanks

April 28, 2008 4:20 AM  
Blogger Jon Senior said...

vincent & lenny: Getting a white balance with a WhiBal or similar is fine, but if your flash is a different colour temperature to the ambient, and you're mixing flash and ambient, then you're going to get colour balance issues. You need to gel the flash to match the ambient, or eliminate the ambient.

April 28, 2008 7:03 AM  
Anonymous Larry Vaughn said...

If you want the image to have a uniform color balance, all the light sources that effect the image need to have the same color balance. To do this, you filter the light sources to get the same color balance and/or filter the camera (film) or change the color balance in the camera (digital).

This used to be done using info available from the film manufacturers which might tell how to filter various lamps. Or, use a color temperature meter.

But I haven't heard much about color temperature meters recently.

So you can put up with some warm light from tungsten or other warm sources, but as mentioned green seldom makes skin tones look good.

So go with the best compromise, turn off the bulbs you don't want to affect the image.

Movie people might put gels on an entire window.

Sounds like the D2x devices to measure ambient color temperature could work, but you still need to filter (and read) each different light source separately to get all the lights the same color, if the intention is to avoid any color shifts.

April 28, 2008 11:13 AM  
Blogger Ken said...

The problem David is discussing is not overall color correction, but changing the color of the strobe to try and match the existing room light. Color correction of the overall image doesn't solve this problem.
For example: Imagine you have a white room and floor, with a window, tungsten and florescent lights in different areas of the room. The tungsten lit area will have an orange cast, the florescent lit area will have a green (or other) cast, while the area near the window will have a blue cast. A person in the middle of the room will have different color lights reflecting off the floor onto the face. This creates a very odd look.

Sorry, but not overall color correction cannot solve this problem, because the lights are all different colors. David wants to alter the strobe's light to match the color of the dominate light, thus uses a gel ON THE FLASH. But what color gel? If you can eliminate most of the lights, leaving just one then you can use the gel to match the strobe to that color. You can't gel the strobe to match two different colored lights. You can stack gels to change the light to a specific color. If you stack a yellow and blue gel, it will turn the light green. But trying to match two different colored lights by stacking gels will result in a third color for the strobe. It just makes things worse.

Vincent: The expodisc won't solve this problem. It only helps you set an overall color balance. It can actually make it worse, since it might see multiple colors and set white balance for a middle value, so nothing will have the correct color.

Lenny: Yes, lens filters are used for film, while digital has electronic white balance which does the same basic task. David is referring to gelling the strobe, not the camera.

Blaise: AutoWB often fails. Better to preset the camera, shoot a neutral card, or adjust it in post (assuming you are shooting RAW).

April 28, 2008 12:01 PM  
Anonymous Ry-Tron said...

Echoing Jon above, the discs are great for getting an ambient reading. Once you have that, ya put gels on your flash to match that reading (or as close as possible). Film and digital, it doesn't matter.

Where dSLR cams work better than film is when shooting RAW and correcting overall white balance on your computer in post. Have your cam set to daylight but forgot to switch to tungsten for that cute shot of your kitty on top of the TV? Adjust the WB in Camera RAW or something similar after the fact, then.

April 28, 2008 12:12 PM  
Blogger djb said...

remember when Fuji came out with the colour neg film about 15 yrs ago that could handle diff colour temps like never before,,,forget the name of it...and the Kokak eventually improved VPS et al to compete.

Made industrial stuff easier thats for sure....and then along came ultra-sensitive-to-K-temps-digital....and we had to take a step back again and cringe with the real wacky light situations..

April 28, 2008 1:41 PM  
Blogger Oliver said...

First I want to say thank you for these wonderful tutorials. This isn't so much a comment on the tutorial itself as it is a comment on the concept of gelling flashes.

I use gels when needed to balance the flash with ambient, but does anyone else find doing so a bigger hassle than it really needs to be? For example, when tungsten lights are turned down, I find them to be warmer than normal CTO. And there are all sorts of variations that require trial and error (switch gel, shoot, chimp).

Is there really no way for flash manufacturers to integrate some sort of electronic means of setting the flash color? i.e. you enter the WB setting you want (or even some kind of synchronization between the flash & camera's kelvin WB mode).

Wouldn't that make the whole balance issue all that much easier??

I know this isn't the best place to suggest ideas, but I know the Strobist is quite influential and I wanna throw out ideas.

April 28, 2008 2:18 PM  
Anonymous Fox said...

I was horrified to find out how gelling for Fluorecent light is complicated when I had to shoot in a classroom with open windows to the side. I gelled my flash, setted the camera WB to fluo, and snapped a few test shots... All turned out Orange. I had no time to fiddle around at all. I ended up nuking the ambian with my flash and shooting ambian. I was pretty dissapointed.

April 28, 2008 3:11 PM  
Anonymous Anonymous said...

Ken's right - it's about matching the strobe to the room's light. It's like this: the room has a color cast from whatever artificial light source is there. Fine, you can alter the WB for that. Now, with the WB altered, toss in some daylight, and the whole thing's color is off balance again. Where did the daylight come from? Your strobe, of course. It's made to flash at daylight color temp. Why not WB the ambient light to daylight, then the scene will match the un-gelled flash, you say. Not so fast - now your flash will effectively have a 30CC magenta cast from the color correction of the fluorescents, just like the old film days if you stuck a 30CC magenta filter on the lens. Solution? Match the strobe to the artificial light so you're not sticking daylight into the shot, then alter the WB to correct the whole shootin' match. How? Gel the strobe.

April 28, 2008 5:53 PM  
Anonymous Nabityphotos said...

I find the best way to gather the color temperature of the lights in a room is to take several shots on the various WB pre-settings. AutoWB doesn't give you any info about the light temperature since it's goal is to adjust for it. So, take a shot on "daylight", if it looks good, then use the flash ungelled. If a daylight shot looks orange, then switch to tungsten (or incadescent) and try again. If it looks green, then switch to fluorescent. Once you find the preset that is the closest to correct, then you know which gels to use. Then it's a matter of choosing a full, 1/2 or 1/4 of that gel. Sometimes it's just a matter of choosing between Daylight and Cloudy.

And, oh yeah, shoot in RAW for final adjustments.

Chimps Ahoy!

-Ron

April 28, 2008 7:09 PM  
Blogger Nald said...

Here in the Philippines, we don't have access to gels.

RAW is the only way to go, right?

April 28, 2008 7:43 PM  
Anonymous lenny said...

When using something like a WhiBal card, you shoot the card in the exact same light as the real photograph which means it will contain the light of all sources.

If you would rather deal with a dominant light source, attempt to shoot the card in the area of the room that is getting most of the dominant light.

It sounds like it doesn't matter which way you go. However, it seems the WhiBal or similar solution is simpler. I think I'd rather just stick with gels as lighting effects.

April 28, 2008 7:54 PM  
Blogger Vincent said...

@Jon
True, but the Expodisc is my personal choice, due to the way it "filters" all light entering the lens into one uniform hue--even flash. I usually meter in camera (P/Av), then set my flash to balance (as per Lighting 101), then switch my lens to manual focus and shoot the scene through the Expodisc to get an overall WB (including the flash), and wrap up with a fairly consistent color to my light.

April 28, 2008 11:03 PM  
Anonymous Anonymous said...

I remember shooting chromes and using a Minolta color temperature meter, carrying a box full of 3" Kodak gels for the lens. Color neg was a life saver. Did I mention I LOVE digital.

April 28, 2008 11:55 PM  
Blogger Emmett Photography said...

@Nald - I also live in the Philippines and have created a set of gels for flashes. You can email me for further information at emmett.photography[at]gmail.com

April 29, 2008 1:36 AM  
Blogger focusfinder said...

Please could you explain the word "chimp" in the context of screen?

April 29, 2008 4:13 AM  
Blogger Jon Senior said...

@lenny: Imagine the following:

You are in a room which has a two equally strong light sources, one from each side. To the left is a tungsten lamp, to the right a window. You put your WhiBal where the subject will stand and set your white-balance. The WhiBal gives you a perfect mixture of the two sources.

Now place your subject. Unless your subject is a cardboard cut out, they are going to have tungsten light on the right of their face, and daylight on their left. Which will not look at all like the colour you balanced for.

These are not different solutions to the same problem, they are different problems. If that is the effect that you're after then it's fine, but don't convince yourself that a flat card mimics the contours of a person (Even Keanu Reeves has 3D!).

@vincent: If that works for you, that's great, but as I said above, it's not doing the same thing and is not a comparable solution.

April 29, 2008 5:32 AM  
Blogger Michael Sink Photography said...

Alright guys, some great discussions here...

Sort of... to those of you claiming an Expodisc or whiBal card is all you need, think again. That will set the WB in camera to be correct based on the ambient light in the scene, so your tungsten lights are no longer orange, but a nice neutral color. Great! Add flash (ungelled) at 5500K (color temp), and your scene looks great, but your subject is now blue! Now, gel your flash with a CTO and WOW, it all matches.

I love my WhiBal! Super accurate, smarter than AutoWB, compact, awesome. Will it balance (and have all the skin tones correct) from multiple light sources? No.

April 29, 2008 7:01 AM  
Anonymous Anonymous said...

If I could add one point: It also depends on what level of contribution the continuous sources make to the overall exposure. Is it equal, one stop, two stops , etc, compared to the strobe? Are the sources themselves actually in the composition? Do your tests for the ratio you like first.

April 29, 2008 11:47 AM  
Blogger ej haas said...

Window green gels CC30G are appropriate for cool white fluorescent in North America. In Thailand the cool white bulbs are less green. I've found that a 1/8 or 1/4 green gel works well here. Other countries may vary, but Lao Myanmar and Malaysia seem to be the same. Often I add a 1/8 or 1/4 CTO gel to warm up the subject, although it will have little effect on the background.
The Fuji color neg film that could handle cool white was Realia and NPS.
Those in Indonesia and the Phillipines who have trouble obtaining gels might try buying online from B&H or Adorama in NY USA.

April 29, 2008 9:40 PM  
Blogger Daniel said...

Recently I shot a video and I used tungsten continous lights along with my own DIY fixture made with four warm CFL bulbs inside an IKEA paper china ball.

I know this site doesn't deal with video but this is where I learn the most about lightning anyway.
The difference matters for flashes but not for color temps.

I had used the warm CFL's before but I hadn't mixed them with anything else. I was surprised to find that they had a green cast when I white balanced for the pro tungsten lights. Maybe I shouldn't have bought the cheapest brand.

Do you people have any suggestion on covering for that? Can I gel the bulbs inside the china ball? Should I buy "better" warm CFL's or are they all the same?

Also I've been thinking about buying some "daylight" fluorescent tubes... are they worth the effort, or will they also have strange casts that won't mix well with genuine lights?

Thanks for you comments and for this site. Incredible resource.

April 30, 2008 4:14 PM  
Anonymous Tobiah said...

I like the part where you say about chimping to find out if it looks more green or more orangey...

What white balance would the cam have to be on to do this? Because auto will adjust itself right? thanks

April 30, 2008 5:03 PM  
Anonymous Anonymous said...

I Noticed while shooting if there is a problem with getting the colors to match just right some post production is in order. If you shoot digital, make sure it is in Raw format. Color balance once for the foreground and once for the background. Make two copies of it and sandwich them together, create a mask to put the together and call it a day. The in camera exposure is still most important and it will save you this step, but when you are in a jam it'll seal the deal.

Of course Photojournalism can't do this, but any other situation works fine.

May 01, 2008 2:51 PM  
Anonymous Anonymous said...

Its amazing how many people completely missed teh point of this topic.

May 14, 2008 12:41 PM  
Anonymous Anonymous said...

Please help:

Got FULL window green filter, but on fluorescent setting on my camera (Canon 30D), using a 580EX, it has a distinct colour cast. Any suggestions? Thank you.

May 15, 2008 10:31 PM  
Anonymous Anonymous said...

Please help:

Got FULL window green filter, but on fluorescent setting on my camera (Canon 30D), using a 580EX, it has a distinct colour cast. Any suggestions? Thank you.

Sorry, should have specified, a distinct BLUE colour cast.

May 16, 2008 7:39 PM  
Blogger My Nikon D300 And My Opinions said...

I have been shooting D300, with two green gel-ed strobes, but when I look close, there still stron green strains in sections of the pictures.
When I went back to the room, (a large office) I realised that the CFL bulbs are actually different brands in different areas of the really large room. Each brand has a different shade of green that it it contributing to the photo, and me with my very good relationship with my client will still have some difficulty leveraging them to replace 120 bulbs of one brand with another...
My present work-around involves not pointing to those sections with mixed CFL brands, instead doing one section at a time...

Thanks, David for all your contributions.

Regards,
Ronnie
http://www.propix.in

June 03, 2008 8:19 AM  
Blogger Petteri said...

I have been looking this information since I got Lee filters sample pack. I didn't had any cluw what gel would be suitable for fluorescents, until now. Thanks also for all these informative comments. Great work!

June 12, 2008 5:03 PM  
Blogger Liquid Rhino said...

That 1/2 Green & 1/2 SunCTO stacked tip is awesome. Works like a champ! Thanks D! =]

October 18, 2009 12:31 PM  
Blogger Eduard said...

I fully support last post 1/2gree+1/2CTO is the answer. Why? I did my homework.
In Canon 50D I can see histograms for each color channel, so it was easy.
First I shoot gray projector screen in fluorescent ambient in fluorescent setting - very good balance, all channels aligned, I was surprised.
Second I put 1/4 green over my Vivitar and kill ambient (250/F8) on same "fluorescent" setting -- result is ugly, all channels was off from each other.
Then I tried 1/2 green, full green - B and G are close, by R is very low. So I decided to push it up and added CTO - bingo, it worked!! Well it was not perfect, by somewhat close, and defenetelly much much better than using just green.

December 13, 2009 10:06 PM  

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