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LIGHT: THE INVERSE SQUARE LAW & COLOR TEMPERATURE

Hey FashionPhotographyBlog.com readers,

Welcome back and hang tight! Last time we are talked about the science behind lighting.

Today’s topic gets a little confusing.

The “Inverse Square Law” shapes EVERYTHING in photography.

What does that even mean?! When opening up a stop, the light doubles. When closing down a stop, the light halves. This is applicable to light as well as all aspects of your camera: aperture, shutter, ISO.

*DISCLAIMER* Before we get into this:

LEARN YOUR APERTURE AND SHUTTER VALUES! It’s the only way any of this will make sense.

As far as light goes, if you move a light x2 as close, it appears x4 larger. If a light is moved x2 away, it appears 1/4 of the original size. Surface Area = Distance ²

As far as the Inverse Square Law goes according to your camera (All numbers here are purely for example purposes)… If you have an aperture of f/11 and open up to f/8, the amount of light coming into your camera will double (same can be said of you change from ISO of 400 to 800 or a shutter speed of 1/60 to 1/30). If you have an aperture of f/11 and stop down to f/16 the amount of light coming into your camera will be cut in half (same can be said of you change from ISO of 400 to 200 or a shutter speed of 1/60 to 1/125.)

Real life example:

A light at 5′ with a meter reading of f/8 gives 100% (correct exposure)

A light at 10′ with a meter reading of f/4 gives 25% (2 stop difference. Your image is now underexposed.)

Basically… As you move away, the cone of light gets wider but weaker. Using the outer cone of light for weaker light output is called feathering and gives you a more diffused light.

Color Temperature

All lights have a different and specific color temperature, which is measured in Kelvins. The lower the number, the warmer the color is, the higher the number, the cooler the color the light gives off.

Be certain to set your own white balance based on the type of light you’re shooting in. White balance in camera makes up for changes in color based on the type of light you’re shooting with. Color shifts will occur when color temperature is not balanced correctly. If you don’t know what type of light you’re in, you can always use Auto White Balance (AWB)- when using AWB the camera figures out (approximately) what the color temperature is of the light source you’re shooting in and shifts colors in camera accordingly.

The most common types of light used in photography are continuous lights and flash.

Continuous lighting, such as hot lights, are.. You guessed it… A continuous form of light.  This type of light, with incandescent bulbs, are tungsten balanced.  There are special bulbs and special lights referred to as “HMI’s.” These lights have bulbs which are balanced to day-light. HMI’s are commonly used in the film industry.

Flashes (Strobes) are short bursts of light and are balanced to daylight. Types of flash include but are not limited to speed lights, mono-lights (single flash units), pack lights (generator and flash head units), ring lights, etc.

Now that you have dealt with all of the boring stuff, check in tomorrow to see how everything from the past two days applies to real life and shooting.

See you tomorrow –

Alana

IMAGE SOURCE:

Feature image & image 1: photography by Alana Tyler Slutsky from her Surrealia series. To view the rest of the photos from this series visit her website.

Image 2, 3, 4 & 5: Alana Tyler Slutsky

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