Incident vs Reflected light and which type gives you better photos :: Digital Photo Secrets

Incident vs Reflected light and which type gives you better photos

by David Peterson 1 comment

Advanced Successful photography has everything to do with understanding light. Light comes from many different sources ranging from natural, such as the sun, and forced, such as flashes and studio and other indoor lighting. By understanding light and its influence on your images, you can better control the outcome of your photo shoots.

There are two essential forms of light: Incident and Reflective. They work both together to create light and apart in their own separate ways. Understanding the difference between the two is a big start to mastering light.


I’ll preface the following by pointing out that this lighting is often what counts in portrait photography, but certainly fine art and photographing objects would qualify.

Incident Light

Simply put, incident light is the light that falls on a subject, whether it comes from a direct or indirect source.

Incident light that comes from direct sources is light such as the sun or a flash or studio light that is targeted at the subject. Indirect sources of incident illumination redirects the light onto the subject. Examples of redirected might be a wall or snow or water from which sunlight bounces back onto the subject. It can also come from a reflector, which also redirects, or bounces, light onto the subject.

Reflected Light

Reflected light is a light source that initiates from the presence of incident light. In other words, it’s the light that bounces, or reflects, off the presence of reflective materials in your scene. Whether they’re in the actual shot or not doesn’t matter. The key is that it’s reflecting light onto your subject.

This means that the light being reflected from surrounding areas, such as walls, water, or other objects that have a reflective quality, has a lighting impact on your image. For example, a white room will reflect more light than a room with dark walls, altering the actual subject brightness and contrast ratio.

In the two images above, there is a lot of reflective light. The top one has reflective light surrounding the woman leaning against a bright, white wall. It also has direct, incident light coming from the sun on her face. The image of the woman on the beach has side incident light, but also reflective light off the water, which has kept the potential high contrast to a minimum.

In summary, an incident meter measures the light that is illuminating your subject, whereas a reflected light meter measures the light that is reflecting from your subject. That’s the lowdown on Incident and Reflected light. With that knowledge, we can now look at how direction and intensity impact your images.

Direction

If you made sense of the above, you’ve figured out that the placement of the direct, or main, light source has a huge impact on your final photo. If you turn on a flashlight, you know that light travels in a straight line. Aim that flashlight at a reflective surface, and the angle of incidence is equal to the angle of reflectance. What does that mean? With direct lighting, the light is hitting the subject either straight at or straight behind the camera. That means it has a zero-degree angle of incidence and, therefore, a zero-degree angle of reflectance. The end result is flat, and often unflattering, lighting.

However, if the light source is moved to the left or right at any degree, it will reflect off other sources and back at that same degree angle. This concept is important to understand so that when you position your light, you can modify it to create depth on your subject and thereby avoiding the flat light.

Intensity

Whatever your light source is, the intensity of the light speaks to the amount of light illuminating from the source and onto your subject. When I talk about intensity, it isn’t limited to just the direct light, it also means the reflective light. Traditionally, intensity is measured with a light meter and controlled with the various techniques, such as diffusors and reflectors.

Sources of Reflected Light

Wrapped your head around the concepts of incident and reflected light? Good! We can move on and discuss the best sources of reflected light.

A white wall. These are quite readily available in any building and come in handy for portraits. Using a bright white wall can balance out the light on the side of your subject’s face if the incident, direct, light is aimed at the right angle.

Water is another source of reflective light. It can be less predictable since it moves, such as with waves. But, it still creates a reflection and needs to be factored into your shot.

Snow, like water, is a strong reflective light. Since it naturally doesn’t move, it’s a little more predictable, but can also have much more intensity to deal with, which brings up its own issues. Even with its intensity, it’s hard to think of a better scenario than a snowy landscape since it’s known to reflect its light to surrounds the subject in all directions.

Each of these scenarios will present their own variety of situations. Not every wall will make for the best reflection or subject position. Water varies in brightness... from rivers and ponds to darker oceans to light blue seas. Snow is the most predictable, but can be uncompromising in its brightness, which means having to work around it or with it in a handful of ways.

Natural light often comes from several directions. Whether from shores or snow-covered landscapes, reflected light can be very useful because it helps reduce the shadowed areas.

Metering the Light

No matter the type or source of light you’re working with, in order to accurately meter the scene to obtain the correct exposure you’ll have to understand two metering techniques that tie into what we’ve been discussing: reflected-light metering and incident-light metering. Until you really know what you are doing with a reflected light meter, an incident meter will generally be a more reliable tool.

Reflected-Light Metering

Reflected-light meters measure the amount of light that is reflected in your scene. It’s the built-in meter that your camera comes with. At the same time, reflected-lighting meters are also available as a feature on many handheld light meters. Reflected light metering is not ideal because it reads from the entire scene and uses an averaged reading based on an 18-percent gray (also known as middle gray). This gray is a standard value designed to provide a safe and predictable exposure for average subjects.

Since these meters assume the subject has a reflectance of about 18% (the same as neutral gray), it sets the exposure accordingly. That's good for a typical landscape in daylight, but not if something lighter or darker is predominant. As we all know, subjects simply aren’t all average.

High contrast includes light and dark extremes that can throw any photographer for a loop. For example, a wedding will be one event that will instantly throw off your reflected-light meter! A bride in her wedding dress being photographed with her husband’s black tux is a scenario that makes it difficult to meter. The problem is, the light meter sees a lot of light in the wedding dress. As a result, the image will be underexposed and the dress will look gray. Conversely, if the reflected-light meter is reading the groom in his black tuxedo, the light meter would see very little light being reflected by the tuxedo and, to balance it to middle gray, recommend a higher exposure than is needed. As a result, the image will be overexposed and the tuxedo will come out looking muddy. These two results will be disastrous to that wedding photographer’s results if they’re not aware of how to handle it.

Both of these issues are the result of measuring the reflected light from the subject instead of the actual light falling on the subject.

Reflected meters are for setting the tonality of a specific spot or small area of the subject. This is a technique that requires a lot of practice, and why we’re lucky to have incident-light meters to turn to.

Incident-Light Metering

A better and more accurate metering method to go with is an incident-light meter. This is a handheld light meter that more adequately measures the amount of light falling on the subject. When you read light before it hits the subject, you will achieve better results every time. Because your reading is independent of the subject, the bride’s wedding dress will record as white and the groom’s tuxedo will record as black ( that is unless he’s wearing a purple one)!

So, how do you use an incident light meter? Start by setting the meter to the ambient metering mode. Next, place the handheld meter at your subject’s position and then aim the dome back at your camera, which is likely on a tripod. Note that most of these meters have a 180-degree angle of view.

After you take your reading, you have the settings so that you can adjust your camera’s shutter speed and f-stop to the idea results indicated by the meter. In cases where you would rather go with a shallower depth of field (i.e. going with a larger aperture), the meter will give you the corresponding shutter speed. This is why an incident meter will give you more consistent results with needing less skill than reflected readings. It sounds like cheating, but it’s quite simply a very handy tool!

Given the choice, most professional photographers would choose an incident meter over a reflected meter 99% of the time. If you're getting tired of the inbuilt (reflected) light meter not working correctly for you, try an external incident meter.

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Comments

  1. Wolf says:

    I'm probably not the only amateur who's using these photo lamps with the cute little white umbrellas for indoor portraits, but I'm really just guessing how to apply them correctly. Perhaps you could make a session for "How to effectively use studio lighting"? "How to place lamps"? "What's the difference between Fluorescent Lamps and Tungsten lamps?", etc.

    I'm sure that many of your 'followers' would appreciate your input on studio lighting. If I have missed an existing article on that, please tell me where I can find it.

    Wolf

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About David Peterson
David Peterson is the creator of Digital Photo Secrets, and the Photography Dash and loves teaching photography to fellow photographers all around the world. You can follow him on Twitter at @dphotosecrets or on Google+.