Strobe Lighting

Strobe Lighting

Written by  John Siskin

 

I find that many people decide to avoid working with strobes because they are frightened of them. In my experience most people cannot understand strobes until they work with them. Even in live classes where there is a demonstration in front of the students, many will not get strobes. But when someone sets up the strobes, for themselves, and does a shot, perfects the exposure, and creates a photograph all becomes clear. As with so many things in life the second time is easy! In the classes I teach there are still challenges with learning lighting, but because the classes are on-line, students have my help for a month. We can work through any problems.

There are two and a half important things about light, and this is any light, not just strobes. I usually start with color: if you mix light sources, say fluorescent and daylight, your shot won't have even color. You camera can, generally, balance to any one color, but not more than one. If you bounce a strobe off a blue ceiling, not only will you have less light, because the ceiling absorbs light, but the color of the light will be changed by the color of the ceiling. The second factor in lighting is the size of the light source: if you use an on camera strobe directly the size of your light source is about one inch by three inches, which is not very big. This will create hard shadows and bright small highlights (Hard light shot). When you bounce off the ceiling the light source is the size of the part of the ceiling you illuminate, probably somewhere between a circle five feet in diameter to a circle twelve feet in diameter. Since every part of your subject is illuminated by every part of this large light source there is generally little or no shadowing in the subject (Diagram 1). If you use an umbrella, or a soft box or a light panel, the light source is the size of this device.

The most important thing you can do with a single light source is to make it bigger. Bigger is softer, always. Getting your light source closer to the subject also makes it softer (light distance). I have seen photographers using small soft boxes at a distance from a subject and complaining about shadowing. If you get the light closer to the subject, or make it bigger, the light will have softer smoother shadows. A bigger light panel (Light Panel), umbrella or soft box is softer than a smaller one. It is the size of the device that matters, not the type of device. The size softens the highlights and reduces shadow, because the light is hitting the subject from more directions. If you are having a problem with shadow it is often better to use a bigger device than to add more lights.

Finally the half important thing: direction. Direction is half important because as your light source is gets bigger it becomes less critical. When the light is coming from more directions the position of the light just isn't as important. If you work with a small strobe mounted on the camera the position is important. Since it is mounted on the camera, the position is often wrong. A really big soft light source, like an overcast sky or a big light panel, does not really have direction. The light comes from many directions. But a small light source will change the photograph depending on direction. So you could place a strobe off to the side of a subject using it as hard light, and get a dramatic image. If you choose another angle the image might just be lousy. With a small light source direction is critical.

The most important consideration with a strobe is how much power it has (strobe power). It is hugely unfortunate that strobe power is measured in watt-seconds on big strobes and in guide numbers for on camera flashes. This adds to confusion unnecessarily. Actually the word flash adds to confusion since it makes the same kind of light, in the same way, a strobe does. Guide numbers are an actual measurement of light output by the flash. On camera units, like Nikon Speedlights, are measured in guide numbers. Larger strobes, including the Alien Bees and Calumet

Travelites are measured in watt seconds. Watt seconds are a measurement of power consumption not light output, however there is a direct relationship between watt-seconds and light. The problem is that the same watt-second rating, on two different brands of strobes, is not the same amount of light. One reason that strobe power is discussed in watt-seconds is that these strobes have interchangeable reflectors, and take accessories like umbrellas, all of which change the light output. Certain things can be said about watt seconds: first if you double the amount of watt seconds, on the same strobe, you have twice as much light, or 1 stop more light. So if you have a 200 watt-second light, and you are working at f5.6, and you double the output to 400 watt-seconds, you will be working at f8. Shutter speed doesn't affect strobes, so long as the shutter speed is at or under the sync speed for the camera. This is because the strobe is only on for about 1/1000th of a second. All the shutter has to be is open. On speeds higher than the sync speed the shutter is never completely open at one time. The duration of the strobe is faster than the shutter curtains.

When I think about strobe power I think about the way I use light. I very rarely use my main light directly, most of the time my main light source is bounced off an umbrella and/or filtered through a light panel (Light panel/Umbrella). This takes a lot of light, as the umbrella and the light panel both absorb some of the light. Consequently for the biggest light in my shot, I often use a 750 watt-second strobe. I know this by practice rather than by calculation. You could get by with a lower power strobe, if you wanted to work at a higher ISO. One thing to consider: a powerful strobe will be brighter than daylight, allowing you to make any ambient light less important in the shot. If you raise the ISO you also raise the sensitivity to ambient light. So if you have bright windows on an interior shot, you may not be able to control the brightness of the window, with a less powerful strobe. A powerful strobe is brighter than daylight. Most continuous lights, like quartz and CFLs are much less powerful than daylight, which really limits the way you can use them. You can use a strobe more efficiently: umbrellas, soft boxes and light panels absorb a lot of light. However a very large light source is not only flattering it is also easy to use. Because of the size, small changes in position of the subject or strobe do not have a large affect on the image. This makes shooting easier.

One of the most effective ways a photographer can use light is to mix hard light and soft light (Hard/Soft light). The soft light from a large light source can give an overall light to the face and reduce shadowing that defines wrinkles and other skin problems. The hard light can be used to give accents to the face or add sparkle to the hair and eyes. While lighting this way takes practice and attention to detail the results can be very effective.

Hard light shot: This uses a small light. You can see the direction of the light. The small light create texture and drama in a photograph.

Strobe power: The powerful strobes allowed me t balance the light inside the room with the light outdoors.

Hard/Soft light: This shot uses I large soft light and several smaller hard lights.
The Soft light creates the smooth light on the face and the hard light defines the cheek and hair.

Hard/Soft light: In this shot the hard light is dominant and the soft light, from a large light source is used for fill.
You can see the subject, but the hard light brings all the character to the shot.

Strobe power 2: Without a powerful strobe I wouldn't have had enough light to work with the bright daylight in this shot.

You can see how a light panel lights a subject from more angles.

Hard/Soft light: A large light source is used near the camera and a smaller one on camera left.
This gives definition to the face. Another light is used for the hair.

Light panel: This homemade panel is a simple way to make a large light source. You can buy these ready made.

Light panel/Umbrella: Here I'm using the light panel and the umbrella together to create a soft even light.

Light distance: The difference between these two images is that the light is much further away in the shot on the right.
So as a light moves back it becomes harder.

© John Siskin

John SiskinJohn Siskin is a commercial photographer who does architectural, industrial, product, and people photography for advertising and promotion. John Siskin shoots macro and micro images for industrial uses and jewelry images. He makes photographs for large and small clients. John Siskin photographs people! I provide photographic services through out Southern California and beyond.