Available light with no flashes at night.
In writing we use italics, bold, quote marks and other techniques to emphasize parts of the composition. In photography we use light to do the same thing.
Theater and movie directors many times use light to draw our attention to the main subject in a scene. This may be as dramatic as turning a spotlight on a character while everything else goes completely black. More often it is much more subtle. Without the light to guide us we might lose the lead actor on stage amidst all the other actors and scenery.
During a concert a spotlight is constantly on the main performer. So rarely are they not in that spotlight that the famous clown Emit Kelly did a comedy act where he tried to stay in the spotlight only to give up in the end and sweep the light up off the floor.
Another way to lead the viewer’s attention to a person or part of a scene in video photography is zooming in on that subject. In TV and film they use multiple cameras to help direct the audience. The director will cut from a camera with a wide view to one showing a close-up of the subject.
Still photographers don’t have the luxury of simultaneous shots zoomed in or out cutting from a wide to a close shot. The still photographer can do all of this, of course, but he or she ends up needing to tell the whole story in a single shot. Print advertising does this all the time.
The still shooter should do all that is reasonable and feasible to capture the image in as high a quality as the situation will allow. (More about that in a minute.)
There are two ways that you can help direct the attention to the main subject using light in photography. One is done in the camera and the other is done in post processing.
Getting it in the camera
Students are taking a test, so I used available light.
With today’s digital cameras it is relatively easy to work with the available light in almost any location.
If people are sitting at a table with poor light move them to a table in better light. After a few moments they’ll pick up on the conversation where they left off and you now have them in light that will work for the photos. In a photojournalistic coverage this is inappropriate, but for advertising or a corporate shoot it is perfectly fine to do.
Use a reflector to help improve the light. It is much less intrusive than flash and can work just as well. Have an assistant hold a reflector just out of the view of the camera and bounce the light back into the subjects face. This helps to draw attention to the main subject.
Used a flash to light his face inside of a furnace/air conditioner blower. No other lights in the room.
You can use either a constant light source or flash to light the subject. Use spotlight effect as much as possible rather than floodlight where everything is lit equally.
Another trick of the trade is to place a colored gel over a light used on the background. This will simplify a junky background by making it all one color. The orange extension cords and red tools hanging on the wall in the background no longer vie for attention with you subject. At least two lights are needed one on the subject and one on the background. The light on the subject should be brighter than the background light.
Using fill flash to capture it in the camera.
This is done so much today that a photo being “PhotoShopped” is now a verb and not just a noun. Before the days of PhotoShop, photographers would “burn” and “dodge” in the darkroom. A face could be lightened and the background darkened.
With digital today you can do even more than we did in the darkroom and with more precision. You can select only the subject, just a single color or anything one part of a photo and alter it in many ways. You can remove, change or add color. You can make objects lighter or darker. Parts of the photo can soften or blurred.
If all this can be done in post processing… why use lights?
Using colored gels to help the background and create a science look and feel.
The need for post processing disappears if you capture it in camera saving time and money.
A properly exposed subject contains information at its fullest value.
When should auxiliary lights be used and not used?
(Here’s the “more on” reasonable and feasible.)
In Hollywood everyone is being paid to produce a professional product people will be willing to pay to see. (Pardon the alteration; I got carried away as always – oops.)
In news coverage the only ones being paid are the news crew or maybe just a single photographer and they are being paid to get the story regardless of the quality. Sure, it should be as high a quality as is practical, but the story is the thing.
The colored carpet and chair colors distracted you now they don't with the gels.
When a photographer comes to do a job, particularly an event, what determines the approach? Can it be with all the lighting using multiple flashes (Hollywood) or will it need to be photographed using the available light (News coverage)?
What is the deciding factor? You need to consider the friction you may cause while capturing the moment.
Perhaps the subject or event can be moved to a more photogenic area that would not require much, if any, additional lighting. Perhaps reflectors can be used instead of flash thus reducing the interference with an event.
You need to explain to the client the choices (and the resulting photos) and together find a solution. (HINT: Whoever is paying for the project needs to decide or this maybe your last job with them.)
Use light to direct attention; it can improve the communication of the composition.