Lighting Ratios? But I Hate Math!
Sublime Light is a web site dedicated to teaching you to photograph people like a pro. For the latest articles, check out the home page.
Higher ratio (~7:1)
sebastian.yepes.in
Guess what…I hate it too!
As a photographer, sooner or later someone is going to use the term “lighting ratio” with you in a conversation. Many hobbiests don’t even know what this term means. In fact, many seasoned photographers still don’t have much of a grasp of what a lighting ratio is.
A lighting ratio is simply the difference in light level between the key (main) light and the fill light. Lighting ratios really only take into account two lights: the key light and the fill light. Any other lights you use in the image are simply accent lights that aren’t taken into account.
Here’s the simple formula:
Power output of first light divided by the second light times 1.695. That's it! So as long as you always keep a calculator in your camera bag, you're all set.
Now if you’re still with me, just forget that last paragraph of horse poo.
How To Determine The Ratio
The only way to accurately find out the lighting ratio is to use a light meter. Many of us don’t own them though. To get close, you can use your camera’s built in meter to determine the ratio. To get it good enough to be happy with your photo, you can even eyeball the light levels. Once you’ve gotten good at seeing the differences in light levels in terms of stops, figuring out a lighting ratio isn’t too difficult.
Lower ratio (1:1)
preciouslife
When a fellow photographer refers to a 2:1 ratio, they simply mean that one light is twice as bright as the other. If you read up on the laws of light, you know that a factor of two means that there’s a one stop difference. A 4:1 ratio means there’s a two stop difference. Did I leave out 3:1? That’s a 1 1/2 stop difference.
In the photo at the beginning of this article, there’s a pretty high ratio. The lit areas are quite a bit brighter than the shadows. I’m going to take a guess that it’s about a 3 1/2 to four stop difference. This puts the ratio at 7:1 or 8:1. The other photo is more evenly lit, with both strobes on equal power. This means the ratio is an even 1:1. It’s probably not exactly 1:1, because to get that the lights would have to be exactly the same distance away from the model.
If you really want some math, here it is, but it’s easy. Just multiply or divide by two. For a 5:1 ratio, simply divide five by 2. This gives you a 2 1/2 stop difference. Want to know the ratio for a photo with a difference of 3 stops? Just multiply three times 2. That’s a 6:1 ratio. Simple.
Does This Only Apply To Two Lights?
While lighting ratios typically apply to controllable lights, a lighting ratio can also be determined between a light and the sun, or a flash and ambient light. If you just have one light with you, different ratios can certainly be made by adjusting your single light.
Why Does All This Matter?
Subscribe
Quite honestly, it doesn’t unless you’re a hardcore photographer. If you just want to get out and take great photos, you don’t need to know this. You’re probably doing fine without it. But lighting ratios are an easy way to communicate lighting setups to other photographers, a universal language if you will. It also tells you the lighting setup irrespective of the key light’s power setting, where it could change depending on the conditions.
| Like this article? | |||
Bookmark it: |
 |
 |
 |
 |
 |
|
 Email It To A Friend |
||
|
Subscribe to feed: 
|
|||
If you like reading Sublime Light, check out the Sublime Light Forums!
| |||
August 21st, 2007 at 9:11 am
[…] Read More… […]
August 31st, 2007 at 9:17 am
Wow, I can’t believe I didn’t comment on this.
Great article. Lighting ratios used to drive me crazy until I learned that a stop doubles or halves the amount of light falling on the subject.
I’m gonna post something in the forums on this.
-Scott
August 31st, 2007 at 11:45 am
I was starting to worry about you Scott
September 4th, 2007 at 5:56 pm
Great article, Tim. I very much endorse the last paragraph, except you don’t even need the “unless you’re a hardcore photographer” part. I was a hardcore photographer for quite a few decades (national book covers and awards) and pretty well ignored lighting ratios. Get the main light right, then fill as much as you feel like, actually works pretty well.
Still, people really need the kind of explaination you’ve given here to make their own judgments about whether to pay attention to lighting ratio, rather than blindly take the advice of some lighting guru on faith.
If you really wanted to persuade people that it’s just not worth the worry, though, you’d have to add in the complication that, while the main light illuminates only the highlights, the fill light usually illuminates both the shadow AND the highlight, and that makes the math a little more complicated still! I could add in a few more complications, but I’ll stop while (I hope) I’m still ahead.
Just listen to Tim’s advice, folks!
September 4th, 2007 at 8:48 pm
Thanks for the input Fil, and the endorsement. You’re absolutely right in that even the hardcore photographers don’t really need to care about lighting ratios unless they really want to. Quite honestly I don’t. But this is a confusing subject for many, so I wrote an article.
And that’s a good point about the fill light illuminating both the shadow and the highlight. If any of you dear readers perked up reading Fil’s comment and wondered why he seems to have a pretty in-depth understanding of light, it’s because he does. Fil is the author of Light: Science and Magic and is the absolute guru of photographic lighting. If you don’t own a copy yet, you should get one. I kid you not it will change how you look at light forever.
September 4th, 2007 at 9:22 pm
Wow, Tim.
You’re getting some top-notch talent on here!
Fil, your book has been enthusiastically endorsed by Clif Hauser of the MAC group. He represents Profoto, Sekonic, and those guys here stateside. I took a seminar with him and he raves about the book. Heck, he said that he was writing a book until he came across yours. He stopped writing it and tipped his hat to you. I took the class twice: last year and this year. He endorsed it both times.
OK, now since you guys are so smart, I have a tough one for you. Your key is f/8. Fill f/5.6. We know that the fill spills. So…how do you compenssate? Do you dial each light down by a fraction of a stop? Leave ‘em as they are and hope no one notices? What? Tim, I was actualy going to put this in the forum a coupla weeks ago!
-Scott
September 4th, 2007 at 10:28 pm
(I’m not so smart; I simply had a good teacher. Ross Scroggs, Sr., chemist, one of the inventors of Ektachrome. He expained everything well, except for lighting. He lit absolutey beautifully, but couldn’t quite tell anyone how he did it. L-S&M is simply the last building block in Ross’s grand scheme; I did only that, he did the rest.)
You’ve pretty well answered your own question. Sure, dial down each light a bit, or leave ‘em the same and close the aperture a bit.
You could also calculate this, if you enjoy the itellectual exercise. The very best book ever on how to do this (although perfectly awful in many other ways) is Mitchell’s (a significant astronomer, a dynamite wine maker, and another of Ross’s disciples) “Photographic Science”. Long out of print, hard to find, but probably pretty cheap, if you can find it used.
Now, tell me how to contact Cliff Hauser. I want to do a new book, and if he’s got some good ideas, I want to talk to him.