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Lighting Glossary

Ambient Light

Ambient light, or available light, refers to the light that already is present in the location where you plan to shoot. This light could be sunlight or indoor overhead lighting. Typically, when using studio flash units indoors, the ambient light will be overpowered by the direct flash. However, it is important to factor in any ambient light in your flash meter readings to ensure a proper exposure.


The aperture is the physical lens opening on your camera. It is adjusted to open and close in f-stop increments, allowing more or less light in with a larger or smaller opening. The iris diaphragm inside the lens of your camera is adjusted to alter the quantity of light that will reach your film. Each aperture opening, or whole f-stop, lets in twice as much light as the smaller whole f-stop before it, and half as much light as the larger whole f-stop after it. For example, f5.6 will let in twice as much light as f8, and half as much light as f4.

Automatic Mode/Automatic Exposure

The automatic mode is a setting on your camera that allows the camera to use its internal meter to automatically adjust the aperture and shutter speed for a shot based on the ISO and the available light. When using studio flash units, you cannot leave your camera in automatic mode, as its internal meter will not be able to detect the light that will be emitted by your flash units, and will thus be set to an inaccurate shutter speed and aperture opening, causing your picture to be overexposed. When looking at your camera’s settings, settings such as P, S, Tv, A, and Av are ALL automatic modes; M is the setting for the manual mode (refer to your camera manual for more info). Note that ISO can be set to Auto as well and must be set manually when used with studio flash units. Auto Focus, however, does not affect exposure and is okay to use.

Average Current

Einstein™ units draw an average current of 5 amps during recycle and AlienBees™ and White Lightning™ flash units draw an average current of 6 amps. This means that if a light were fired every time it recycled, the average current draw would be 5 or 6 amps. At the beginning of each recycle, the lights draw a peak current of about 16 to 18 amps for about 200 milliseconds. This is well tolerated by household circuits and breakers. A typical circuit breaker will tolerate three flash units in normal use. When the lights are idle and not being fired, the current draw is essentially that of the modeling lamp - 1 to 2 amps per unit.

Beam Candle Power Seconds (BCPS)

Beam Candle Power Seconds is the measure of effective intensity of a light source when it is focused into a beam by a reflector or lens. It is the effective intensity for a period of one second - a function of actual light output (candle power, or CP) as well as the modifier used (which is what turns it into a focused beam), very much like guide numbers. Modifiers can focus a light from almost omni-directional to an incredibly small point of light. A 100 CP light source and 100,000 CP light source can produce the same amount of light on a given point from the same distance, depending on how the light is spread. For example, if you take one AlienBees™ B400 unit with our 7AB/R 7-inch reflector (which spreads light 80 degrees) and another B400 with our 11LTR 11-inch reflector (which spreads the light 45 degrees), you will get two different BCPS measurements, even though the same amount of light (lumenseconds) is used. If you take our B400 with the 11LTR and a B1600 with the 7AB/R, you will get the same BCPS (at least closer), but you are emitting more light (lumenseconds) from the 1600 to do so. Lumens can be converted to candle power (1CP = 12.566 Lumens), though comparing the two different measurements is much like comparing kilograms to pounds per square inch. To illustrate this comparison, consider a 1 ton elephant (weighing 906 kg). Place the elephant on a cone, which focuses the weight to 1 square inch, you have 2,000 pounds per square inch (or 906 kg per square inch). Place the same elephant on a 2,000 square inch piece of plywood and you now have 1 pound per square inch (or .43 kg per square inch). The elephant weights the same. See also Lumenseconds.

Bounce Lighting

Bounced light is an indirect light source, where the actual light is pointed away from that which you wish to illuminate, and bounced off of a reflective surface back towards your subject. This can be achieved in flash photography with reflector panels, umbrellas, and even reflective surfaces such as a wall or ceiling. Bounced light is used when you desire a softer, less harsh light quality than is produced with direct lighting.


When shooting, bracketing is taking several photographs of the exact same scene and setup with different exposure settings both above and below the target setting indicated by the flashmeter. As different brands of flashmeter vary in their readings for a “correct” exposure, bracketing both above and below the indicated settings will ensure that you get a properly exposed picture. If, for example, the indicated exposure for a setup is f5.6 with a shutter speed of 1/60 second, you can bracket for one stop less at f8, and one stop more at f4. When using the Cyber Commander™, the FLASH EXPOSURE BRACKETING option allows you to leave the camera settings the same, but change the flash output in the “BRACKET FLASH” screen.

Color Balance / Color Temperature

The color temperature refers to the color of a light source, measured in Kelvin. The color balance refers to the relationship between the color of light and the film. See also Kelvin.


The contrast is the degree of difference between the dark and the light areas of a scene or photograph. High contrast photographs are a result of high contrast lighting, where there are sharp differences in the dark and light, and less in between. High contrast lighting can be achieved with both direct and bounced light that is not softened or diffused, but often reflected from a bright silver surface.

Depth of Field

The depth of field refers to the nearest and farthest points in your photograph that are in focus in your shot. A lens can only focus on one single distance fully, but with a wide depth of field, areas both closer and further from that one point are relatively in focus as well. Stopping down to a smaller aperture increases the depth of field, and will result in more of the photograph being in focus.

Diffused Light

Diffused light is softened light, with less shadows and more even coverage. A diffused light source is most commonly achieved by directing light through a translucent material, such as a diffusion shoot-through umbrella, a softbox, or a diffusion reflector panel.

Effective Wattseconds

This terminology was originally used in 1985 by Inverse Square Systems in conjunction with their "Stroblox" series of high-efficiency self-contained flash units. The term was created because most manufacturers of flash equipment (as well as the press) insisted on the incorrect use of the term "wattsecond" as a definition of light output (in such wrong statements as "This system puts out 800 Ws of light"). Since the Stroblox system produced on the order of twice the amount of light per wattsecond as did the average "box-and-cable" system at the time, Inverse Square Systems chose to employ the rating "2400 effective wattseconds" as a means of saying "our system puts out an amount of light equal to the average 2400 Ws system,” even though the actual stored energy of the Stroblox 2400 was only 1200 joules or wattseconds. Indeed, this terminology gave the user a more clear idea of what to expect from the unit than he would have gotten had they simply stated that it was a 1200 Ws system. See Wattseconds.

Fill Light

In a lighting setup, the fill light refers to the light source which is used to “fill-in” the shadows cast by the main light. This source can be a flash unit, or simply a reflector that is directed on the subject to illuminate the shadowed areas and lessen the contrast.


A filter or gel for a flash unit is a thin piece of tinted or colored gelatin placed directly over the light source to alter the quality of the light’s output. Gels will physically change the color of the light, whereas filters will modify its quality. We offer color gels, warming filters, diffusion filters, UV filters, and neutral density filters.

Flash Duration (t.1 and t.5)

When a typical variable voltage flash system fires, although it may appear so to humans, the light emitted does not come on and go off instantaneously. In reality, the flashtube "turns on" very quickly and then dims gradually as the flash capacitors discharge. When the tube is fired there is a rapid ionization period as the tube output rises to maximum brightness. This is followed by an exponential decline in tube current, voltage and light as the capacitors are discharged to zero. The standard engineering term for stating flash duration is t.5. This describes the time that it takes for 50% of the total flashpower to be dissipated. Whenever the simple designation Flash Duration is specified, it can be assumed to be the t.5 specification. However, the t.5 specification doesn’t adequately predict the actual motion freezing capability of a flash. There is a much longer trailing edge that continues to emit the remaining 50% of the light. This causes considerably more motion blur than the t.5 specification implies. In order to better compare flash duration specs to an equivalent shutter speed, the term t.1 was introduced by the photo industry. The t.1 specification indicates the amount of time that it takes for 90% of the total flash to be emitted. But even following the t.1 time there is still light being emitted at sufficient intensity to cause some ghosting or motion trails. Flash units using variable voltage power control (including the Paul C. Buff™ AlienBees™, White Lightning™ X-Series and Zeus™ flash systems) typically exhibit an increase in flash duration roughly equal to 20% of the full power flash duration being added for each full f-stop in power reduction. Conversely, flash systems using IGBT control (including the Paul C. Buff™ Einstein™) offer faster flash durations as the power is decreased. In an IGBT flash, the voltage and current remain constant as power is reduced and that power is reduced by abruptly shutting the tube off once the desired amount of light has been emitted. This results in flash durations that become shorter and shorter as power is reduced, as well as the virtual elimination of the exponential flash tail that is responsible for motion blur. This is illustrated in the figures below.


An f-stop is a designation to indicate a camera’s aperture opening. It is also used to describe a change in exposure (from changes in aperture, shutter speed, ISO, flash output, etc.) equivalent to one f-stop change in the lens. Each f-stop (shown on the back panel of our flash units) lets in twice as much light as the f-stop before it, and half as much light as the f-stop after it. For f-stops in relation to your camera’s lens opening, see Aperture. For f-stops in relation to flash adjustment, see Power Variability.

Guide Number

The Guide Number (GN) is a standard measurement serving to indicate a flash unit's output by calculating the distance times the f-stop, with respect to the film speed, relating the film speed to the actual flash output. A guide number is determined by placing the flash unit at a desired distance from the subject (usually 10 feet) and metering with an accurate flash meter. The guide number can be calculated from the distance and the f/stop (GN = f/number x flash-to-subject distance). The term is not wholly reliable for comparing flash units because it relates more to the angle of the reflector than to the actual amount of light produced. For example, a flash unit with a given amount of light output will register a much higher guide number (f-stop at 10') if it has a narrow angle reflector (for a telephoto lens) than if it has a wide angle reflector. The actual amount of light is the same in both cases, it just covers more area with the wide angle reflector (at a lower guide number). In comparing flash units, the max GN of a flash unit is usually given for ISO 100 film. When it comes to choosing a flash unit, you have to be careful, as these measurements can be altered. It is common practice within the flash unit industry (for marketing reasons) to provide the max GN at the smallest coverage, as this will provide the longest focal length. Such a focused flash unit is more powerful, which produces a higher guide number, implying a more powerful output. Therefore, the max GNs of different flash units are usually not directly comparable. Studio flash units are designed to be used in many different configurations with different accessories. The angle of coverage will be different in each case as will be the achieved guide number for a given amount of emitted light. As merely an indication of output, we publish the max guide numbers, noting that they are not true measurements of what you can do with our lights, as the real output will be determined by how you choose to modify the light.

Highlight / Hot Spot

Highlights or hot spots are very bright, well-lit and often overly lit areas in your setup. Hot spots appear when one area of your scene is overly lit, and can be avoided by diffusing or lowering the output of light on that area.

Hot Shoe

A hot shoe is a u-shaped mounting point, usually found on the top of SLR cameras. The shoe provides slide-in mounting of small, battery operated flash units. In addition, it provides an electrical circuit connection which fires the flash when the shutter is tripped. If your camera does not have the necessary PC-connection to wire our flash unit sync cord, you can purchase a hot shoe adaptor piece, which fits in your hot shoe, and allows the sync cord to be plugged into your camera.

IGBT Power Control

Essentially all low power camera flashes (speedlites) employ IGBT control of flash power instead of the variable voltage control that is used in most larger studio flash units (in, for example, the Paul C. Buff™ AlienBees™ units). IGBT technology is easily implemented in low power units, but only recently have IGBT devices become available with sufficient power handling capacity for use in higher powered studio flash, especially those offering fast flash durations. Flash systems using IGBT control (including the Paul C. Buff™ Einstein™ units) offer faster flash durations as the power is decreased. In an IGBT flash, the voltage and current remain constant as power is reduced and that power is reduced by abruptly shutting the tube off once the desired amount of light has been emitted. This results in flash durations that become shorter and shorter as power is reduced, as well as the complete elimination of the exponential flash tail that is responsible for motion blur in non-IGBT flash units. See also Flash Duration.

IEC Standard Connector

An IEC is a standard connector system for removable power cords on electronic equipment. These power cords are found on just about all computer equipment and are also widely used in electronic test equipment. This connector system is used on all Paul C. Buff™ flash unit power cords.

ISO (International Standards Organization)

The ISO established and promulgates standardized methods for measuring the “speed” of photographic film or its sensitivity to light. The results are commonly referred to as a film’s “ISO Number.” The higher the ISO number, the more sensitive the film or sensor is to light.


Quantity of electrical energy is measured in wattseconds, also known as joules. See Wattseconds.

Kelvin (K)

The Kelvin is a unit of temperature measurement starting from absolute zero at -273 Celsius. Degrees Kelvin (or color temperature) is used in color photography to indicate the color balance or spectrum of light emitted from a light source. If you were to heat a chunk of iron to 3000 Kelvin, the light emitted from the iron (a dull red glow) would be said to have a color temperature of 3000K for the purposes of color photography. Sunlight measures about 5500K and film balanced for sunlight (daylight film), will assure 'true' color rendition for objects reflecting the sun. Photographic, or Xenon, flash creates a light source with a color temperature of about 6000K. AlienBees™ flash units come with a standard flash tube which measures 5600K, and is daylight-balanced for film.

Lens Flare / Light Spill

With ambient and studio lighting, when light is directed or refracted into the camera's lens, this light is known as lens flare. Some photographers will allow light to be reflected in their camera's lens for an intended glowing effect, but normally light spill is undesired. When using studio lighting to illuminate your subject, you can eliminate light spill by positioning your flash unit and accessories to not direct light back into your camera. Lens flare can look like a light haze has washed across the image or it can appear in the form of lighter lines or circles.


A Lumen is a unit of measurement of light intensity emitted by a light source. A lumensecond refers to a light of 1 lumen intensity for a duration of one second, or the equivalent, such as 2 lumens for half a second. The absolute amount of light emitted each time a flash system is fired is correctly specified in lumenseconds. The number of lumenseconds produced by a particular flash system depends on the efficacy, how effectively the system turns electrical energy into light energy, or wattseconds into lumenseconds. The efficacies of commercial photoflash systems typically fall within the range of from 15 to 50 lumenseconds per wattsecond. What this implies is quite simple: a highly efficient 300 Ws system may produce as much actual light energy as an inefficient system rated at 1000 Ws.

Main Light

The main light in a lighting setup is the primary light used. This primary light source is typically the brightest in your setup, casting the most prominent shadows.

Manual Exposure

Manual exposure is a camera mode which is non-automatic, and requires the photographer to set their own aperture f-stop, shutter speed, and ISO for each shot. This mode does not rely on the camera’ s internal metering system, but requires you rather to take a reading with a separate flashmeter to determine correct settings. When using external flash units, your camera should be adjusted manually. Note that your focus mode does not affect exposure and either manual focus or automatic focus can be used. When looking at your camera’s settings, settings such as P, S, Tv, A, and Av are ALL automatic modes; M is the setting for the manual mode (refer to your camera manual for more info).

Modeling Lamp

In order for the photographer to be able to visualize what the scene is going to look like when the picture is taken, studio flash units contain modeling lamps. These are incandescent lamps of modest power that are placed in the studio flash in such a position as to mimic the light that will be emitted by the flash when the actual picture is taken. Modeling lamps help the photographer see where the light will fall on the subject and where shadows will form. With all Paul C. Buff™ flash units, photographers can use the modeling lamps to provide a What-You-See-Is-What-You-Get (“WYSIWYG”) preview of the actual shots as the lamps are capable of accurately tracking flashpower adjustments, providing a constant relationship of modeling Lumens to flash Lumenseconds, with errors no greater than 1/10 to 2/10f at any power setting. Additionally, the modeling lamps in all Paul C. Buff™ units are positioned so that they project similar beam patterns to the flash. Modeling lamps, like the flash, should be immune to variations in power line voltage in order to maintain consistent accuracy regardless of fluctuating power lines. In this regard, all Paul C. Buff™ studio flash systems employ high-precision voltage regulation of both modeling lamps and flash to provide consistent output at all power line voltages from 105 to 135 Vac.

Monolight / Self-Contained Flash Unit

The terms monolight and flash unit are often used interchangeably. A monolight is a self-contained flash system that incorporates the power supply and flash head in one package. This term is used to distinguish these systems from power pack systems where the power supply and flash head are separate and are connected using a heavy duty, custom cable. Monolights draw their power directly from standard wall outlets. The AlienBees™, White Lightning™ and Einstein™ flash systems are examples of self-contained flashes; the Zeus™ system is an example of a separated power pack and flash head system.

Power Variability

Power variability refers to the number of individual whole f-stop settings available on a studio flash. A flash that has 6 individual stops of adjustment (1/1, 1/2, 1/4, 1/8, 1/16, 1/32) has a 6 stop power variability and a 5 f-stop range, or 5 incremental settings away from the starting point (1/1, or full power). Some flash manufacturers incorrectly use the term “range” to indicate the number of individual settings on a given flash, i.e. the same flash with 6 stops of power variability would be advertised as having a “6 stop range”. Since they are including the starting point, this is incorrect. We use the term “power variability” to correctly state the number of full stop settings available on our flashes.

Proportional Modeling System

The modeling system aids the photographer in the composition of a shot by providing a continuously burning light source that imitates (models) the flash illumination. In order to be defined as proportional, the modeling light must imitate the flash in two important respects. First, it must provide the same pattern with various modifiers (reflectors, softboxes, barndoors). Secondly, it must accurately track the flashpower in order to show lighting ratios when two or more lights are used in a setup. The modeling lamps in Paul C. Buff™ units are designed to provide a What-You-See-Is-What-You-Get (“WYSIWYG”) preview of the actual shots as the lamps are capable of accurately tracking flashpower adjustments, providing a constant relationship of modeling Lumens to flash Lumenseconds, with errors no greater than 1/10 to 2/10f at any power setting. Additionally, the modeling lamps in all Paul C. Buff™ units are positioned so that they project similar beam patterns to the flash.Your multi-light setup may include different models of flash units with varying output. For example, your setup may include one AlienBees™ B1600 unit and two B800 units. As all three units arrive with the same 150 Watt modeling lamp, the preview will not accurately show the difference in output between them. The higher-powered B1600 model at full power produces more light than the lower-powered B800 model at full power, but using identical modeling lamps will make it seem that they are of equal brightness despite the output difference. To maintain an accurate, proportional preview with a multi-light setup that includes different output models, you can use the Cyber Commander™ as part of the CyberSync™ system or you can use modeling lamps of relatively lower wattage in the lower output flash unit models. With the CyberSync™ system, the Cyber Commander™ can compensate for setups containing flash units with different wattseconds ratings and modeling lamp wattages, maintaining accurate proportionality between the modeling preview and flash exposure. If you wish to achieve an accurate preview by physically changing modeling lamps, you can simply replace the supplied modeling lamps with lamps whose wattage ratings are relative to the flash power. For example, in a setup using AlienBees™ B1600 (640 Ws), B800 (320 Ws) and B400 (160 Ws) units, you could use a 150 Watt bulb in the B1600 unit, a 75 Watt bulb in the B800 unit and a 40 Watt bulb in the B400 unit.


When you fire your flash unit, it releases all of the energy stored in its flash capacitors in order to emit the flash of light. Before you can fire the unit again, the capacitors must have time to recycle, or build up enough energy in the capacitors in order to fire again. Fast recycle times are important for rapid shooting, as you can take shot after shot without pausing to wait for your flash unit to keep up.


A ringflash is a flash that can encircle the lens of a camera. This type of flash produces on-axis light that creates a unique "halo" shadow on the background, or can be shadow-free. A studio ringflash is an invaluable and instantly favorite tool of the professional photographer due to its ability to produce essentially shadow-free lighting, revealing unique catchlights in the eyes of subjects when used with fashion and portrait work. Paul C. Buff™ offers two ringflashes: the self-contained AlienBees™ ABR800 ringflash and the Zeus™ ZRM1 ringflash head (part of the Zeus™ system, requiring a power pack). Ringflashes are also popular as on-axis fill lights.

Shutter Speed

Shutter speed is a term which refers to the length of time your camera’s shutter is open. As the shutter opens and closes to expose your film, the shutter speed measures in seconds the length that light is reaching your film. Obviously, the longer the shutter speed, the more light you are letting in. Very fast shutter speeds will allow you to stop action, but require a great deal of light. With flash photography however, the flash duration dictates action-stopping. See also Flash Duration and Sync Speed.


A flash unit is said to be a slave flash when it is set to fire by detecting the flash from another (master) flash unit in a multi-light setup. This allows multiple flash units to be operated with only one light synchronized (hardwired) to the camera. As many slaves as necessary can be used in a setup. All studio flash units from Paul C. Buff™ have highly sensitive built-in slaves (which can be disabled if desired), allowing the units to be fired whenever they "see" the flash from another flash unit.


The sync connection in a flash system physically connects the flash unit to the camera body, either to a PC connector or through the hot shoe. This circuit is used by the camera to fire the flash at the precise moment that the shutter has fully opened and before it begins to close, to successfully capture the full light burst from a flash (or flashes). Each Paul C. Buff™ flash unit and power pack arrives with a PC-connection sync cord for syncing to your camera. The flash units can also be synced using remote controls, such as our CyberSync™ system and LG4X™ remote control. See also Sync Speed.

Sync Speed

The sync speed for your camera (identified by your camera manufacturer) indicates the fastest shutter speed that you can use with your flash unit in order to successfully capture the full light burst from a flash (or flashes) while the shutter is fully opened and before it begins to close. On most modern cameras this is typically between 1/160 and 1/250.

Sync Voltage

The sync voltage (or trigger voltage) rating refers to the voltage between the camera and the flash unit when connected by the supplied sync cord from the flash unit's sync jack to the camera's PC connection jack (or hot shoe). When using digital cameras, it is best to check the maximum sync voltage allowed for your specific camera. Many brands of flash units have sync voltages much higher than ours, some as high as 50-60V, but the sync voltage on all current Paul C. Buff™ flash units is under 6 volts, safe for use with digital cameras. The sync voltage on some of the older, retired White Lightning™ models was higher: 9.5 volts on the retired Ultra Series units, 12 volts on the retired ZAP 1000 units, and 24 volts or higher on on the retired WL5,000 and WL10,000 units. When using these units with a digital camera, you will want to use a safe sync adatper (such as the Wein Safe-Sync Hot Shoe to Hot Shoe High Voltage Sync Regulator, available from B&H and other similar photo equipment stores) to reduce the voltage to safer, lower levels. Alternately, you could use the CST CyberSync Transmitter and either the CSR or CSRB receiver to wirelessly fire the unit.

Through-The-Lens Meter (TTL)

A TTL meter is a light/exposure meter that is built into your camera and takes light readings through the lens to determine the correct settings when in automatic mode. It cannot be relied upon for determining the correct exposure settings with external flash units.


Quantity of electrical energy is measured in watt seconds, also known as joules (one watt second is equal to one joule). This rating defines the amount of electrical power discharged with each flash. This rating defines the amount of electrical power discharged with each flash. While the actual amount of light produced for a given number of wattseconds varies, depending on the unit's design, the term provides a reasonable guide to comparative light output, as long as real/true wattseconds are specified. In the conversion of watts to lumens, or wattseconds to lumenseconds, the efficacy of the system determines how much light will result from a given number of wattseconds. The poor efficiency in this conversion by manufacturers has given rise to the term Effective Wattseconds. If one flash system converts 400 wattseconds of energy into 16,000 lumenseconds of light, and another flash system converts 800 wattseconds of energy into 16,000 lumenseconds of light, then the first system could claim to have "800 Effective Wattseconds" as it is effectively producing the same amount of light as a system starting with 800 true wattseconds. The Effective Wattseconds rating, however, is rather arbitrary and cannot be easily proven true or untrue, as it is merely used as a basis for inflated comparison of different flash systems.