Portrait Lighting For Beginners: Laws of Light
This article is part of the ‘Portrait Lighting For Beginners’ series. This series is meant to help you go from a beginning photographer to making beautiful portraits.
I wonder how many of my readers ran like the wind when they read the title of this post. “Oh crap, here he goes talking about laws of the universe and physics, I’m outta here!” Not to worry, I’ll keep this short, to the point, and most importantly, simple. So here we go.
The Basic Laws (In no particular order)
- Large light sources give you soft light, and small light sources give you hard light.
- The closer a light source is to the subject the softer the light, and the farther away the light source is, the harder the light.
- The closer a light source is to an object, the brighter it is.
Law 1. Size and Softness
This one seems pretty straight forward. The larger the light source is, the softer and more diffuse (or fuzzy) any edges of light and shadow will be. A tiny pinpoint light source will give you hard shadows. For portraiture, larger light sources to achieve softer lighting is traditional. This is accomplished using umbrellas, softboxes, and other tools which we’ll talk about shortly. That’s not to say that soft light is best, it’s just traditional.
To see this rule in action, try a little test. Sit your significant other down on the couch next to a table lamp. No significant other? Try holding your foot out, but keep an eye out for the neighbors, because believe me you look foolish. Good. Now take off the lampshade and observe the hard, bare bulb light that comes from the small light bulb. Put the shade back on and observe how the light becomes soft because the shade is now the light source, and it’s a lot bigger than the bulb. Doesn’t your foot look nicer in soft light? Or maybe that hard light was hiding something you didn’t want seen in the shadows. There you go, that’s why you shouldn’t be afraid to break the rules. But I digress.
Easy enough, right? Big = soft and small = hard. On to law 2.
Law 2. Distance and Softness
After reading the first law, you might ask “Hey, but the sun is as big a light source as we know here on planet Earth. Why is the light from the sun so hard?” That’s a good question, and any book on lighting uses this example when explaining the laws of light.
The sun may be huge, but the distance is so great, that its apparent size to us is tiny. So this one really just flows right into the first law. If you were to take a one inch light up close and a ten inch light ten feet away, when looking at them, they would appear to be the same size. They would have the same lighting effect (as far as softness, intensity comes next).
So while a Speedlight flash might seem small and give hard lighting when taking a picture of your girlfriend, that same light would give you very soft light when it’s positioned right up next to a ladybug. The close position makes it seem enormous, and thus softer.
Law 3: Distance and Intensity
Okay, if you’re still reading, you know that this stuff is really easy. Don’t fail me now. This is the hardest part, but still really simple.
Light diminishes rapidly, and not in a linear way. This is known as the inverse square law. Now, if this were a physics class, I’d go ahead and explain it, but since we’re photographers, and thus creative beings, I’ll leave that alone. Math? Screw that.
Here’s the meat of it: the further away a light gets from an object, the less light falls on that object. The key here is that changes in distance have a bigger effect the closer the light is to an object. If you have a light set up ten feet from an object and you move it five feet back, it’s going to have a much bigger effect than if you moved it from 100 feet to 105 feet. The first move would be dramatic, while the second would have nearly no effect whatsoever.
The key here is that light increases and decreases in a very predictable way, and now that you know the law, making adjustments with your lighting will be much easier and less hit and miss. Sometimes when taking pictures, it’s easier to just move the light than to adjust the power setting because it’s quicker, and because you know exactly what the effect will be thanks to the inverse square law.
Most explanations of the inverse square law involve a bunch of math and trying to wrap your head around concepts. The way I look at it, if you spend more time trying to figure out numbers than actually taking pictures, you’re doing yourself an injustice.
Exercise
What? Homework? Yeah yeah, I put that there for fun. But there are a couple of things you can do before we start the next section to help you understand light better.
- Try the lamp shade trick above.
- Try some pictures with different size light sources and observe the effects.
- Try taking some pictures in a dark room with nothing but a single lamp. Take a picture, then have the subject move double the distance from the lamp. Take another picture. Observe the effect on the intensity of light. Have the subject move again and take another picture. Now, start over, but at each step, change the camera’s exposure (use manual exposure mode) to allow one more stop of light to enter. This means the shutter speed is slower or the aperture is wider (or a combination). If the subject moved the right distance, the exposure on that image and the previous step should be the same, with no drop off in light.
Got questions or comments about this post? Why not post them in the discussion thread dedicated to this series of articles? I promise, there are no stupid questions, only stupid people. Just kidding, none of those people read this blog…
It just so happens that David Hobby over at Strobist wrote a post about this very same topic at the same time I did. He did a great job of explaining this concept, but with a little different twist on it. I highly recommend you read it. It can only do you good.
EDIT (7/9/2007): Mr. Strobist created a new post today that explains in depth the idea of apparent light size. I give it a thumbs up, and recommend you check it out.
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July 3rd, 2007 at 10:06 am
great info, simply put
July 12th, 2007 at 4:31 pm
Agree with Luis – feel free to submit to http://www.photographyvoter.com
July 12th, 2007 at 4:35 pm
Thanks to both of your for the compliments. I really appreciate it! Feel free to spread the word that I’m out here doing this!
Cheers!
July 17th, 2007 at 6:29 pm
thanks for sharing
July 31st, 2007 at 10:36 pm
thanks man..finally i understand it
October 30th, 2007 at 10:08 pm
Doesn’t the inverse square rule say double the distance, quarter the light?
December 31st, 2007 at 1:43 pm
Great description. doubling or halving distance now allows me to move subj or light if locked in by shutter speed or aperture limits and get close to correct exposure quickly.
January 11th, 2008 at 6:31 am
John lowe’s right, you know – the article is good, but it’s misleading. Light intensity decreases according to the inverse square law, therefore to decrease the light falling on an object by one stop, you have to move the light root 2 (about 1.4) times as far away, and vice versa. Moving it twice as far away will decrease the light by two stops, not one.
Love your pages on portrait lighting techniques, by the way – I’m just being picky here!
January 21st, 2008 at 6:59 am
These are some great articles perfect for any dSLR Dad on the principles of lighting and lighting setup. Great work Tim.
http://www.dslrdad.com
December 9th, 2008 at 8:09 am
Butter gun! My physics teacher used the butter gun analogy to explain inverse square.
Think of a … wait, lets google…aha…
http://www.youtube.com/watch?v=JW3tT0L2gpc
I can’t believe it, the actually made a butter gun to demonstrate. I love the internet.
February 2nd, 2009 at 7:37 pm
“The closer a light source is to an object, the brighter it is.”
So if watch a lamp towards a white wall, we’ll see the spot on the wall get brighter? For sure. We also observe the bright spot on the wall getting smaller at the same time it gets brighter.
So if we watch the reflection of a lamp in a mirror, as the lamp is moved towards the mirror we see its reflection get brighter? Well, no. The image of the lamp in the mirror gets bigger, while it stays the same brightness. (More total area, hence more light, but the same light density.)
Thus closer does not necessarily mean brighter. Whether one is observing mostly diffuse reflections or mostly direct reflections from an object will impact whether the observed object gets significantly brighter or stays basically the same brightness as a lamp is moved closer to it.
March 23rd, 2009 at 8:17 pm
i’m still not understand how to setup for low key portrait shoot. Any drawing where is the speed light, camera and object placed? Kindly please provide also the aparture , shutter speed and also speed light meter setting and the xample of potrait with the setting. Thanks
July 14th, 2009 at 6:50 pm
@Wayne VanWeerthuizen
I’m not entirely sure I agree with you. I do film lighting, so I understand the principles if lighting quite well. The idea that and object doesn’t appear brighter because it’s a diffused or bounced source is quite confusing to me.
Lets say we have a polystyrene board that has a light source directed on it which is then bouncing at the subject. If the DoP told me the subject needs to be brighter, one of the first things I do is move the move the light source closer to the polystyrene board. D.o.P. is usually happy with the change.
Maybe I just misunderstood what you meant.
July 15th, 2009 at 4:10 pm
I meant to say “If we watch a lamp move towards a white painted wall” (or in your case a sheet of polystyrene), “we will see the spot on the wall get brighter.” With the light far away, we get a spread out, but dim, spot. When the light is moved right next to the wall, we see a much more concentrated spot on the wall: smaller and brighter.
When we put a mirror where the wall is and move the lamp in the same manner as before, this time the brightness of the spot we see in the mirror does NOT change, although we still see the image of the lamp in the mirror get bigger, which results in increased *total* light getting to us from the lamp. But the image of the lamp in the mirror is the same brightness whether it is close to the mirror or far away – it’s the same brightness as the lamp itself.
Total light is not the same thing as brightness – brightness is rather a measure of light density, that is, the amount of light *per unit area*.
Walls, and your polystyrene boards, exhibit mostly diffuse reflection, which means light hitting them from one direction is reflected in multiple directions. In the case of a mirror or shiny metal, the light hitting it from one direction is all reflected in a single direction – that’s a direct (also known as specular) reflection.
Another way to think of the same effect, if you are taking a photo of several identical candles viewed in a mirror, where some candles are significantly closer to the mirror than other candles – the spots from all the candles will be the same brightness! But the closest candle casts a much larger image. (Same as if the candles were photographed directly, without the mirror.) But if there is a painted wall behind the candles, how far each candle is from the wall will affect how bright a spot the candle casts upon it.
This also applies when photographing metals. If the lighting creates a highlight that is unacceptable due to being too bright – moving the light in a straight line further away from the metal won’t fix it. Rather, one has to actually dim the light itself or put something in front of it, or move the light so it’s at a different angle where it doesn’t create the unacceptable highlight at all. (Another option may be to use a dulling spray on the metal, making its reflection less specular and more diffuse.)
The book “Light: Science and Magic” by Hunter, Biver, and Fuqua explains all this in even more detail.
March 1st, 2010 at 8:47 am
I may be misinterpreting your interpretations…
It seems to me the Law number 2 above is reversed.
The same intensity of light farther away seems softer the when moved in closer to the subject.
If it is farther away it would spread out more, making it softer.
March 1st, 2010 at 1:34 pm
John,
When a light get further away, it does indeed spread out. However, most of that spread out light doesn’t hit the subject, so no, it’s not softer.
However, when a light is up close, it’s hitting the subject from more angles, thus wrapping around the object more and making the lighting softer.
Try it! Get a light and umbrella (or just a lamp and a lamp shade). Move it super close to an object in a dark room. Now move it ten feet away. Ignoring the difference in brightness, you’ll see that indeed the lighting is harder when it’s further away.
March 27th, 2010 at 7:06 pm
I am mildly amused by the responses here. The series is called “Portrait Lighting for Beginners.” Tim Solley explains basic lighting principles in a way that the BEGINNER can easily understand them. But people who are obviously NOT beginners have to have their say and get into the technical aspects of lighting.
Tim, you’re doing a great job explaining this stuff in a way that we can understand it. All you professionals, you are also doing a great job NOT explaining the stuff in a way that’s easily understood. Remember, this “Portrait Lighting FOR BEGINNERS”! Again, Tim, thanks for explaining the concept in an easily understood manner.
April 14th, 2010 at 4:58 am
Tim this is an outstanding article and a great site. I conduct a workshop and I will be using some of your stuff. Actually I just gave this lesson last night. Photoman022 it is true that pros are coming and making something simple so complicated however it is the nature of the beast. This is my first visit to this spot, but I am sure I will be returning.
May 17th, 2010 at 10:27 am
WOW! thank you for keeping it simple…I was just hateing the idea spending my day inside reading artical after artical about light meaters ratios to get a better understanding… You have made it so EASY now I can go practice…once more THANK YOU!!!