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< Product Resources < Lighting Resources
Introduction to Packs & Heads
Part: 1 2
Choosing Electronic Flash Packs and Heads
Power packs are designed to accept and power a number of flash heads via extension cables, and are relatively transportable. Power pack systems are quite versatile – some allow asymmetrical -- or uneven distribution of power from each of their outlets to the flash heads.
Interchangeable reflectors and light modifying attachments for lamp heads allow you to determine where the light will fall, and how diffused or focused that light will be. The use of multiple heads with lights strategically placed and modified, is the key factor that differentiates professional from amateur images.
Power packs are rated a number of ways
Guide Number
Defined as the f/stop times the distance of a given ISO rating. For example a guide number of 110 will result in an exposure of f/11 at 10' with ISO 100. Guide numbers are usually specified for ISO 100 at 10 feet.
BCPS (Beam Candle Power Seconds)
Beam Candle Power Seconds. Used to measure light output of a flash unit. The flash head is aimed at a calibrated meter, usually at a distance of 10'. This rating will vary depending on the reflector used in the test.
Watt-Seconds
The term “Watt-Seconds” describes the amount of energy stored in the capacitors of an electronic flash power pack. Because of the great flexibility in modifying the lamp heads of most pack systems, “Watt-Seconds” cannot be used to determine the true light output that will be used to expose your subject.
Other factors effecting performance include: Efficiency of the electronic components, the design of the control circuitry, lamp head, the type of flash tube, the length of the cables, reflectors and other accessories used. When comparing units, consider power claims as only one of many factors in your decision-making process.
There are many aspects to consider before deciding on the lighting system that’s right for you. First, determine what the intended use of your flash purchase will be. Then, understand what the advantages and disadvantages of the various electronic flash systems are. Then, carefully compare the brands and as many features as possible that meet your requirements. No product or brand can do everything for all situations. However today’s electronic flash pack systems are extremely versatile and one will certainly be ideally suited for your special needs.
Light output is usually the major consideration when looking for electronic flash equipment. However this is only one of many factors that should govern your choices. Remember there are many factors that will determine the actual light level exposing your subject. The ratings of a power pack and flash head does not take into consideration the substantial effect reflectors, umbrellas, light boxes, room size, number of lights, ambient light condition, and subject matter have on the actual amount of light that will be needed to properly expose the subject.
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