What are Continuous Lighting Sources?

Studio Lighting Basics, Part III

When photographing people I've never been 100 percent comfortable using studio flash units. They are a necessary evil for making portraits when available light isn't available. An alternative is hot lights, or continuous lighting.

Even though digital capture gives me the instant feedback formerly provided by expensive Polaroid proofs, I prefer continuous light sources, especially for portraits. Instead of the subject being distracted (and blinking) thanks to the repeated pop of electronic flash, continuous light sources let them relax.

Hot Lights

For years, photographers have used photoflood, tungsten, quartz, and all kinds of continuous light sources that fall under the general heading of "hot lights." These light sources have many advantages over flash: They can be inexpensive; they let you see the light as captured, allowing you to use your camera's in-camera meter; and they are generally smaller and lighter than electronic flash units.

On the downside, working with hot lights often creates problems because of their color temperature (See "Color Temperatures?") and they are, waddaya know, hot.

White Balancing Act

For digital photographers, dealing with mismatched color temperatures is a thing of the past. Most digital SLRs include settings for tungsten light and some will even let you dial in a specific color temperature in Kelvin. For the first shot, don't forget to try the camera's Auto White Balance (AWB) setting. Many times this setting will produce perfect color the first time without any color temperature gymnastics.

If all else fails, you can use the camera's built in controls to create a custom white balance for a specific lighting set-up. The key for doing this is having a dependable "white" color source that can be used to calibrate your camera.

My favorite white source for custom white balance is the flip side of the redoubtable Kodak Gray Card. One side of the card has the infamous 18-percent gray and the other has 90-percent reflection aka "white."

Hot lights come is several flavors including Photofloods, HMI, and Quartz. Each system has its own unique characteristics as well as pros and cons.

Photofloods are physically a simple combination of a housing, light stand bracket, and reflector. They use incandescent bulbs that are not all that different from the bulbs in your lamps at home, and are almost as inexpensive. As with all bulbs used in hot light systems, they are relatively fragile and should be handled with care. Always have a few back-up bulbs in case one breaks before or during a photo session.

Studio lighting doesn't get much cheaper than this Smith Victor Adapta-Light that has a 10-inch reflector. It costs around $35 and that includes the bulb. Extra bulbs cost approx. $4 so when you buy an Adapta-Light be sure to buy a few spares.

HMI (Hydrargyrum Medium arc Iodide) lights have several advantages over standard incandescent or quartz lights. When compared to incandescent lights they deliver five times the light output per watt and generate less heat. Unlike quartz the color temperature of HMI lights is the same as sunlight and doesn't require an on-camera filter or a tungsten color balance setting inside the camera. Originally designed for the film and video industry, HMI is a flicker-free light source that's also recommended for digital still photographs that require long exposures. The bad news? They're pricey.

The Arri Compact 1200 HMI Fresnel Light with 6.89-inch Lens, 1,200 Watt, 100 Volt Supply Voltage, 6000°K output costs approximately $2,270.

In between Photofloods and HMI is the Goldilocks of continuous lighting, the quartz light. It's available in sizes, shapes, and prices to suit almost everyone's lighting budget. Quartz lighting fixtures use high-pressure incandescent lamps containing halogen gases whose filaments burn at higher temperatures with higher efficiency, producing more lumens per watt than an incandescent lamp. Quartz does not darken with age but get extremely hot so be careful to avoid burnt fingers and let them cool off before touching one of them.

The Lowel DP is a long time quartz lighting workhorse. A $290 kit includes, 1000-Watt bulb, barndoors, and light stand. Get a spare lamp too. They only cost around $19.

Cold Lights

The only problem with traditional "hot lights" is that they are, well, hot. They're not all that comfortable to work under for subject and photographer alike. Welcome to a new world of continuous light sources powered by fluorescent bulbs. I know what you're thinking: Aren't fluorescent lights those thingies that produce horrible green light when shooting slide film?

Yes...but: As it turns out, daylight-balanced fluorescents also happen to be the perfect light source for digital photography. Tungsten lights produce 93 percent heat and only seven percent red light. By comparison, fluorescent light is cooler, brighter, and comes out the winner for color balance.

(Here's the technical explanation; skip it if you're not technical: Fluorescent-based lights used for photography are daylight-balanced and their RGB output spikes closely match the receptive RGB spikes of a CCD or CMOS imaging chip. A CCD is least sensitive in its blue channel and tungsten light has the least output in the blue and when combined with infrared output (that's the heat) it can overcome the chip's spectral response. Here's a look at three different kinds of cold "hot" lights.)

F.J. Westcott's (approximately $364) Spiderlite TD5 is designed for still or video image-makers. It has a built-in speed ring for attaching a lightbank and three separate switches that permit multiple combinations of the lamps to be turned off and on to vary the output quantity. A handle allows for quick and easy rotation for a head that accepts either Halogen or Fluorescent Lamps. Halogen lamps produce a consistent but hot 3200 degrees Kelvin and the fluorescent lamps are rated at 5100 degrees Kelvin, although that seems to vary as the lights warm up.

The Spiderlite's fluorescent lamps provide smooth continuous light. By looking at each image file's histogram, you can use your digital SLR's Exposure Compensation feature to gradually increase exposure in one-third stop increments to make sure exposure is balanced.

The Sunpak MDL-600 AC Digit Lite 600 uses fluorescent tubes that are balanced for daylight and does a good job of emulating the real thing. I often use the it as a main light or sometimes as a beauty light placed below a model's face the way I formerly used a reflector back in the old film days. There are some who shoot with available light, but what they really mean is "every light that's available." I hate to schlep all that stuff. That's why the Sunpak works so well for my "shoot and scoot" style of photography.

The Sunpak MDL-600 AC Digit Lite is a 600-Watt continuous fluorescent soft light unit that has a color Temperature 5600 degrees K.

Ego Trip for eBay shooters

Lowell's Ego is a tabletop sized fluorescent light that a breeze to setup: Attach it to a lightstand and turn it on. The Ego includes two 27-Watt screw-in daylight fluorescent lamps that have a 5,000 – 10,000 hour rating. Lowel also includes a small white card that can be used as a reflector. When using the Ego as a main light for portraits, be sure to place the light as close as possible to the subject without getting it in the shot.

A single Lowell Ego ($100) sets up quickly and when used with a reflector is placed close to the subject whether it's a portrait subject or still life. A $200 two-light kit (see it in action at the top of this article) is perfect for photographing products for sale on eBay!


Who is this Kelvin guy, and what's his deal with color temperatures?

In the nineteenth century, Lord Kelvin (right) urged the elimination of negative values when measuring temperatures and suggested that an absolute zero temperature should be the basis for the scale. Higher Kelvin color temperatures are at the cool (blue) end of the spectrum. On the lower side, light sources are on the warmer (red) end of the spectrum. On a clear day at noon, the sun measures 5500 degrees Kelvin (Kelvin is often shortened to "K"). On an overcast day, the temperature rises to 6700 degrees Kelvin, while you'll experience 9000 degrees Kelvin in open shade on a clear day. Traditional hot lights have a temperature about 3200 degrees Kelvin while household light bulbs usually measure about 2600 degrees.

Joe Farace is the author of a new book called "Getting Started in Digital Imaging" published by Focal Press (ISBN 024080838X.) It's available in all the best bookstores as well as Amazon.com.



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