WATT-SECONDS VS. GUIDE NUMBER
Unlike a guide number (GN), the watt-second rating isn’t affected by any devices that shape or modify the light. So a 300 watt-second monolight remains a 300 watt-second monolight, even with an umbrella or softbox attached, whereas the effective GN would be reduced. Purchase a monolight based on the watt-second rating, not the GN.
A monolight’s controls are often found at the rear, but may be on the side of the unit instead. You can dial down the amount of juice that goes to the flashtube. Why? To reduce recycling times, or to use larger ƒ-stops, or to just lessen the impact of this light without otherwise modifying the lighting. That literally can be done with a dial or digitally, sometimes with a switch. Ideally, the range should be at least 3 stops, but preferably 4 or 5 (or more), stepless/continuous or in 1/10 increments. As a rule, the greater the range, the more expensive the monolight.
As you decrease output, you’re decreasing voltage supplied to the flashtube, and that will produce a cooler (bluer) light. To counter this effect, many microprocessor-controlled studio strobe systems boast a “constant color temperature” so color balance is maintained at all output settings. There’s also an alternative option to hardwire sync in the control panel on many monolights. It may involve a photocell, infrared trigger or even a radio remote receiver—all of which require an optional external triggering device.
Let’s Take a Closer Look
The monolight has a housing that’s usually metal or high-impact polycarbonate, or a mixture of the two. The housing terminates at the front end in a metal reflector, or dish. By the way it’s designed, the reflector shapes the light, giving that light a harder or softer edge while controlling the light’s throw. The standard reflector is fine for starters. You may not have a choice if it’s permanently attached. The reflector should be slotted to hold a photographic umbrella or, alternatively, there should be some provision for an umbrella attached to the housing.
The flashtube is visibly the most important part of the monolight. While it does last quite a long time, eventually a flashtube goes bad or gets damaged. We suggest you choose a monolight that accepts user-replaceable flashtubes so the unit doesn’t have to be sent to a service center. You also may want to replace the supplied flashtube with a UV-coated or color-corrected flashtube so that it produces a more neutral-colored light that’s closer to true daylight balance. Select monolights already come with this type of flashtube.
Other Things You Should Know
Studio strobe output, whether monolight or powerpack, is rated in watt-seconds (sometimes incorrectly referred to as “watts” or “watts per second”). Many monolights are rated in the neighborhood of 300 watt-seconds to 500 watt-seconds at the low end, but more powerful units may go to 800 watt-seconds or more. This is actually a measure of the stored energy inside the capacitor that’s available to light your subject. Usually, the higher the energy rating, the more expensive the monolight—and the bigger and heavier it is.
The modeling light, my friends, is perhaps the biggest selling point for choosing a studio flash over a speedlight. This is a constant light source that helps you visualize the lighting. It’s not perfect, but comes awfully close to replicating the pattern of light from the strobe. That said, once the lighting has been established, feel free to turn off the modeling light. If you leave it on, it should automatically quench or dim each time the strobe is fired so as not to contribute to the exposure.
The modeling light should be proportional to the strobe output to give you a truer sense of the lighting, or manually dimmable if you need a light while working. Incandescent bulbs make for poor modeling lights. If possible, opt for 3200K halogen bulbs, which last longer—and they can be used as primary lights on occasion. Wattages in the neighborhood of 60W to 150W are popular with low watt-second monolights, but low-wattage bulbs are difficult to use in bright ambient settings. Higher wattages of 250W or more come with more powerful strobes. That said, use only the wattage, shape and type of modeling lamp recommended for that unit. (Note: Don’t handle a halogen bulb with bare hands, as the oils on your skin may damage the casing, causing it to shatter.)