Watt second
Encyclopedia
A watt-second is a derived unit of energy
equivalent to the joule
. The watt-second is the energy equivalent to the power of one watt
sustained for one second
. While the watt-second is equivalent to the joule in both units and meaning, there are some contexts in which the watt-second is used instead of joule.
The kilowatt hour (kWh) is equivalent to 3,600,000 watt-seconds and is a unit used in the electricity market
, and by producers of electricity.
The distinction between joule and watt-second is not analogous to the usage of newton meter for torque
despite being an equivalent unit to the joule.
is the watt-second. A flash can be rated in watt-seconds (e.g., 300 Ws) or in joules, but historically the watt-second has been used and continues to be used. The energy rating a flash is given is more of a technicality than a true benchmark in terms of light output because there are numerous factors that affect the energy conversion efficiency. For example, the actual construction of the tube will vary the efficiency but also the use of reflectors and filters will change the usable light output at the subject. Some companies specify their products in "true" watt-seconds and some specify their products in "nominal" watt-seconds. http://www.imaginginfo.com/print/Studio-Photography/What-Is-A-Watt-Second/3$1043
Companies that use watt-seconds to describe their products:
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
equivalent to the joule
Joule
The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...
. The watt-second is the energy equivalent to the power of one watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
sustained for one second
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....
. While the watt-second is equivalent to the joule in both units and meaning, there are some contexts in which the watt-second is used instead of joule.
The kilowatt hour (kWh) is equivalent to 3,600,000 watt-seconds and is a unit used in the electricity market
Electricity market
In economic terms, electricity is a commodity capable of being bought, sold and traded. An electricity market is a system for effecting purchases, through bids to buy; sales, through offers to sell; and short-term trades, generally in the form of financial or obligation swaps. Bids and offers use...
, and by producers of electricity.
The distinction between joule and watt-second is not analogous to the usage of newton meter for torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
despite being an equivalent unit to the joule.
Photography
In photography, the unit for flashesFlash (photography)
A flash is a device used in photography producing a flash of artificial light at a color temperature of about 5500 K to help illuminate a scene. A major purpose of a flash is to illuminate a dark scene. Other uses are capturing quickly moving objects or changing the quality of light...
is the watt-second. A flash can be rated in watt-seconds (e.g., 300 Ws) or in joules, but historically the watt-second has been used and continues to be used. The energy rating a flash is given is more of a technicality than a true benchmark in terms of light output because there are numerous factors that affect the energy conversion efficiency. For example, the actual construction of the tube will vary the efficiency but also the use of reflectors and filters will change the usable light output at the subject. Some companies specify their products in "true" watt-seconds and some specify their products in "nominal" watt-seconds. http://www.imaginginfo.com/print/Studio-Photography/What-Is-A-Watt-Second/3$1043
Companies that use watt-seconds to describe their products:
- ElinchromElinchromElinca S.A. is a company based in Renens, Switzerland, which manufactures studio lighting systems under the brand name Elinchrom. Competitors include Bowens and Interfit.-Range:...
- Paul C. Buff/Alien Bees
- ProfotoProfotoProfoto is a photographic equipment maker that produces studio lighting systems mainly for photography purposes. In 2010, the company expanded its business into the movie/video lighting industry. Profoto was founded in 1968 by Eckhard Heine and Conny Dufgran...
See also
- Guide numberGuide numberThe guide number for an electronic flash measures its ability to illuminate the subject to be photographed at a specific film or sensor sensitivity and angle of view...
- Kilowatt hour, a scaled unit of the watt-second often used in the electrical energy industry