Strobes & Flash
In a still photography world, strobes were the gold standard of professional lighting gear. Prized for their combination of power and performance and for their ability to freeze a subject for maximum apparent sharpness, strobes continue to be top-level tools for just about any photo situation.
Being a professional photographer often requires the ability to produce beautiful light on demand, whatever the subject,anytime, anyplace. Generations of proshad just two types of light sources—strobes and hot lights—but lately a third category has been making waves: continuous cool lights. Here’s a rundown of the nuts and bolts of light source options, including their strengths and weaknesses, to help you construct a more robust and versatile lighting arsenal.
When it comes to the maximum light output for still photography, nothing beats strobes. Their high output is ideal when you need small apertures for maximum depth of field, or when you need to throw light over long distances, or if you need to balance your light with other bright sources like the sun. The other benefit of a lot of light is that it’s easier to modify; when you start with a powerful source, you can scrim it, diffuse it and cut it without running out of light.
Portable Flash Vs. Studio Strobes
There are two main categories of strobes: portable flashes (the kind that can fit on the hot-shoe atop a DSLR) and studio-style strobes. Studio strobes can be further broken down into pack-and-head systems and monolights—the latter has all of the capacitors and controls built into each head, while the former relies on a central pack to control the output to each head.
Of these strobe options, pack-and-head systems offer the greatest output. Strobe power is measured in watt-seconds (Ws), which is equivalent to joules. A 400 Ws strobe is equivalent to a 100-watt light bulb illuminated for a four-second exposure. You can see, then, how a 1200 Ws or 2000 Ws light is all kinds of bright.
As for flashes, their output is measured by guide number. There’s a useful equation for calculating exposures based on guide number, and it’s also handy for comparing one flash to another: GN = F x D, or guide number equals ƒ-stop times distance. If a flash has a guide number of 80, at 10 feet from the subject, the correct exposure is ƒ/8. A guide number of 110 at 10 feet produces an ƒ/11 exposure, illustrating that the second flash produces twice the light—a full stop more.
TTL & Being Wired
Portable flashes have the benefit of optional TTL (through-the-lens) control. These flashes work in conjunction with DSLRs to read the amount of light reflecting off the subject and terminate the flash output at the appropriate moment. Strobe manufacturers, who for years produced equipment that required manual control, are starting to incorporate their own remote controls for triggering and output adjustment, as well as actual wireless TTL connectivity.
Speaking of connectivity, another benefit of small flashes is their compact size, low cost and battery power. Studio strobes can simply be plugged into an AC outlet and run indefinitely, but the ability to shun AC power and produce bright light in even remote locations gives portable flashes—and even battery-powered strobe systems—a distinct advantage. Pack-and-head systems allow you to plug in a single electrical outlet and power multiple lights—often, up to six or more heads from a single pack—while monolights are each powered individually. For working across great distances, a handful of monolights can be spread out as far as there’s electricity to reach them.
Because strobes have long been the de facto standard, there are tons of modifiers and accessories available for everything from small flashes to studio strobes. A single softbox can work with a variety of different brands and configurations with just the change of a speedring or mounting bracket.
Power: You Get What You Pay For
Compared to entry-level continuous light sources, strobes can be fairly expensive. But when you factor in the amount of light they deliver, the power-to-price ratio of all but the costliest studio strobes is favorable. Strobes and flashes can also improve the appearance of sharpness; because longer exposures aren’t necessary and because strobe durations are so short, they eliminate all but the most egregious camera shake and subject movement.
Strobes and flashes can also do something no other light source can do: Because of those extremely short durations (often, 1/1000th of a second and much faster), strobes can freeze fast action and allow the ambient exposure to be adjusted independently of the strobe exposure in the same click of the shutter. Adjusting the shutter speed from 1/60th to 1/125th has no effect on a strobe with a duration of 1/2000th, but it sure will change the ambient exposure. This opens up a whole world of creative possibilities no continuous light can replicate.
Continuous Hot Lights
In a still and motion world, these traditional movie lights have emerged as powerful options for hybrid shooters. Many photographers like the soft, warm look hot lights can give to a portrait. They aren’t suitable for all situations, but hot lights have some definite advantages.
The broad appeal of continuous lights is that, unlike strobes, they can also be used for video, as well. In this age of convergence, continuous lights are practically a necessity for the well-heeled professional.
See The Light
Continuous lights offer WYSIWYG convenience—what you see is what you get—and hot lights are perhaps the most economical lighting available. In their simplest form, they resemble hardware store work lights: a parabolic dish reflector, a socket and an incandescent bulb. Higher-end models incorporate high-output quartz tungsten lamps or daylight-balanced HMI lamps and often Fresnel lenses that focus the light from flood to spot. This style of hot light defined 20th-century movie and television production, partly because the Fresnel lens focuses the pinpoint source into a beam that more closely emulates the characteristics of sunlight better than any other type of artificial source. Some hot lights are known as PARs because, instead of a Fresnel lens, they utilize a parabolic reflector.
Hot lights are so named because not only do the units themselves get incredibly hot (too hot to touch, in fact, requiring the use of leather gloves), they send heat toward the subject. That’s an important distinction because hot lights can be uncomfortable for talent and heat up a set quickly, particularly in close quarters. This can be a challenge when working with food or other subjects that will wilt or melt. When used improperly or with low-grade accessories, hot lights becom
e downright dangerous. As such, there’s a robust offering of heat-resistant accessories and light modifiers, as well as barndoors and scrims to cut and shape the output. With tungsten hot lights, simple dimmer switches can be employed to provide stepless dimming from full power down to nothing.
Power & Price
HMI hot lights are more expensive than their tungsten counterparts, but they also put out considerably more light. Measured in lumens, or the actual amount of visible light emitted, a 400-watt HMI delivers an amount of light roughly equivalent to a 1200-watt tungsten lamp, and because the HMI lights use ballasts, they can be plugged into regular 110 outlets. (Old-style magnetic ballasts for HMIs are less expensive, but much bulkier and quirkier. For instance, once they’re turned off, they require a cool-down period of several minutes before they can be lit up again. Tungsten hot lights don’t have this issue.) If you’re trying to match daylight, gelling a tungsten light reduces its output even further, widening the gulf between tungsten and HMI.
Many tungsten kits include lights in the 150-watt to 650-watt range. For serious lighting power, though, and a source that delivers a lot of light (and heat), there are 1000-watt, 2000-watt and even 5000-watt (and higher) options. These are known as 1K, 2K and 5K, respectively, and whether they employ quartz tungsten bulbs or HMIs, they typically require very heavy-duty stands and accessories, and even could require a generator for power. These are the kind of lights used on movie sets to stand in for the sun.
Continuous Cold Lights
Fluorescent and LED lights have exploded in popularity alongside HDSLRs and the emergence of hybrid photography. Compact LEDs allow you to have extremely lightweight, battery-powered lights, and along with fluorescents, they give you easy color control, as well.
A decade ago, there wouldn’t have been much to write about continuous cool lights for photography, but the technology has boomed in recent years, partly because HDSLRs have turned many photographers into cinematographers, too. Improvements in sensor signal-to-noise ratios mean higher ISOs can be used, so less light is needed. Compared to hot lights, continuous cool lights—in the form of fluorescent tubes or light-emitting diodes (LEDs)—don’t deliver as much pure lighting power, but they’re considerably more compact, more energy-efficient and don’t get hot. They must also overcome the dreaded "green spike" that can cause sickly color shifts, though the best LED and fluorescent fixtures have largely eliminated the problem. They’re incredibly convenient light sources, but if sun-caliber power is what you need, other options probably will work better than LEDs and fluorescents.
Cool & Efficient
Unlike hot lights, continuous cool lights don’t give off much heat—at least not in the direction of the scene you’re photographing. This makes them safer and more comfortable since you can place them close to subjects and touch them without gloves.
In their most affordable form, fluorescent continuous lights use Edison base screw-in bulbs, albeit larger, higher-wattage versions than standard household CFLs. To increase output, many of these fixtures have multiple sockets—two, four, six, even as many as nine lamps fit in a single fixture that increases the amount of light. The bulbs are fairly inexpensive, available in a variety of color temperatures, and can be mixed and matched to subtly warm or cool the fixture’s output.
Beware Of Flicker
Pro-caliber fluorescent lights use biaxial (or biax) tubes and external ballasts to produce more consistent color temperatures and flicker-free output crucial for video. When dimmed, fluorescents are more likely to flicker, not a big problem with stills, but a huge problem for video. Technically, all light sources flicker, but the flicker is most pronounced with fluorescents. In addition to being brighter, the best of these lights are also considerably more expensive.
Because of their lower power consumption, continuous cool lights are less expensive to operate, and their bulbs last a very long time. With the compact size and ultra-low power needs of LEDs, they can easily run on batteries, so they’re extremely useful for remote locations where access to electricity is scarce.
Light Source Size & Color
LEDs are commonly sold as panel lights. Like most fluorescent fixtures, these produce inherently softer illumination than single-source hot lights or strobes. This is helpful with portraiture. The downside, though, is because each light consists of multiple sources, it can be difficult to shape the light, cut it or create a hard-edged shadow. (LEDs are also starting to show up as single-source-style Fresnel and PAR fixtures.) The big benefit of LED lights is that they can be varied from daylight to tungsten, with the best models allowing for specific Kelvin temperatures to be dialed in. Multiple panels can be mounted together to create a larger "light wall" source. This, though, is only for big spenders when you consider a 4×4 array of LED panels could easily cost upward of $10,000—remembering that it’s less than $500 for a professional hot light and a 4×4 silk.
For macro subjects and on-camera fill, LED lights are even available in small hot-shoe-mountable sizes that are extremely compact, and unlike Fresnel hot lights, LED panels are preset for flood or spot. Some less expensive LED lights have built-in cooling fans that can be a challenge for video applications where sound comes into play.
The dimensions of a panel and the quantity of LEDs are often delineated in a fixture’s specifications, but the actual light output is measured in lux, which is a quantity of lumens over a given dimension. The lux measurement makes it possible to compare lights and determine which will provide the greatest usable output.