Watts per what !?

[jared_b.]

I have 3 studio strobes, But I think it's time for me to upgrade.

 

I have a few questions...

 

I read about all these lights, and they say "500WS" and "1250WS", or

what ever the light may be. What exactly is this. The strenght of

the output, yea. What number is considered a strong powered one.

 

 

I want to upgrade so something that has a very strong output, and

something I can have complete control of the output, so I could set

it anywhere between 1/10'th strenght, to full power. Does anyone

have any suggestions or answers ?!

 

Thanks alot :)

 

Jared

[jbq]

Those are not watts per anything. Those are Watt-seconds, i.e. Joules, and that's a measurement of energy. The exact way to write it is Ws (there was a Mr Watt, but not a Mr Second, so Watt is written with a capital letter, but not second).

 

500Ws is what you get if you have a flash that averages a power of a million Watts for a duration of 1/2000s. It's the same amount of energy as you'd get with a 100W bulb and an exposure of 5s.

 

Those are all measurements of electrical energy, not of light output. Depending on how efficient your tubes are, 500Ws might be a lot of light, or not much. A long time ago, all flash tubes had approximately the same efficiency, so that you could compare the electrical energy and have an reasonably accurate comparison on light output. Some tubes are now a lot more efficient than others, but the photography world still insists on using Ws as a pseudo-unit of light output, which led some manufacturers to use "effective Ws" as a measurement of light output. As an example, the low-end Alien Bee has a light output of "400 effective Ws", i.e. it outputs approximately as much light as an old 400Ws tube would; it does it by using only 160Ws of electrical energy.

 

500Ws (500J) is quite a big amount of energy. It's enough to lift a weight of 37 pounds to a height of 10ft, or to increase the temperature of a fl oz of water by 7.3 degrees F.

 

Lots of people here recommend Alien Bees, the biggest one is 1600 "effective Ws", and can be set to 1/32 power.

[phoneguy]

Look <a href="http://alienbees.com/flash.html">Here</a> and clink on the "AlienBees specs" button at the bottom of the page. They have a great info page on what you are looking for. To top it off, you'll already be at a website that has great lights.

 

Mike

[Ed_Ingold]

Watt as a proper noun (i.e., Sir James Watt) is capitalized. Watt as a unit of energy is not. A watt-second is an obsolete term. The proper term is "joules" (with apologies to Mssr. Joule). The units represent power times time (e.g., watts times seconds), or energy. In a capacitative discharge (e.g., an electronic flash), the energy in joules is equal to the capacitance in farads (sorry Mr. Faraday) times the voltage (Mssr. Voltair had nothing to do with this - pity).

 

All else being equal, the exposure value is proportional to the energy in joules. A 1000 joule flash would give 1 stop more exposure than a 500 joule flash. The actual exposure depends much more on the reflector and any modifiers - a fact used to exaggerate guide numbers.

 

How much is enough? In a studio, 500 joules is probably OK. 1000-2000 joules might be needed for a big soft box. 4800 joules might be marginal for a basketball game.

[msitaraman]

<i>"500Ws (500J) is quite a big amount of energy. It's enough to lift a weight of 37 pounds to a height of 10ft..."</i>

<br><p>

 

Or a 185 pound human to a height of 2 feet!

;-)

It doesn't work exactly that way, but its a very good reason to treat studio flash with respect, and be sure of quality before you buy used. Or new.

<br><p>

IMHO, only. I'm not a studio flash guy...

[ellis_vener_photography]

<I>I read about all these lights, and they say "500WS" and "1250WS", or what ever the light may be. What exactly is this. The strenght of the output, yea. What number is considered a strong powered one.</I><P>

Waat-second (or joules) is ameasure of energy stored in the capacitors of the flash or monolight. But it is not directly a measure of how much light the flash has the capacity to produce. That wil ldepend on the efficiency of the design of the flash and the reflector or diffusion or light modifier being used. "Strong" is a relative term. For a small subject like a head and shouders portrait being lit by medium sized softboxes or umbrellas used close to the subject a maximum capacity 500 w-s per light is usually plenty. For larger subjects (full length or group portraits) lit with larger softboxes 1200 w-s would be the minimum maximum power I'd want and I'd be a lot

mopre comfortable with 2400 w-s packs.

 

Brand recommendations (in no particular order): Broncolor; Elinchrom; White Lightning; Alien Bees; Speedotron (Blackline); Profoto Acute 2; Profoto D4; or Dyna-Light.

 

Softboxes; Chimera; Calumet Illumina; Westcott, or Plume Wafer.

 

Umbrellas: Photek, or Westcott.

[gluteal cleft]

"Or a 185 pound human to a height of 2 feet! ;-) It doesn't work exactly that way, but its a very good reason to treat studio flash with respect,"

 

Hey, it'll send them a lot farther than that if they get zapped. But of course, that's cheating, the flash's energy is just triggering a release of chemical energy already stored in the vitim's body. =)

 

steve

[Jeremy Stein]

Just a correction to the physics statements above: a watt is a unit of power (energy delivered per unit time) and is equal to one joule per second. The energy stored in a capacitor is NOT CV (farads times volts), but is (CV^2)/2, and may be expressed in joules. To repeat: energy stored in a capacitor is 1/2 times capacitance (in farads) times the square of the voltage the capacitor is charged to. Oh, and one more thing: while we're pointing out who things are named for, let's not forget Alessandro Volta, for whom the volt is named.

[ilkka]

Yes, and Watt is actually VA (Volt Ampere), and Ampere was of course named after Andre Ampere.

[luis alvarez torres]

Did I miss my science class or what?

[kelly_flanigan1]

rE <i>Yes, and Watt is actually VA (Volt Ampere),</i><br><br>Volt Amperes and watts are different. With volt amperes they voltage and current can be out of phase; and thus not watts at all!<BR><BR>Connect pure inductor or pure inductor to an AC line and there will be current, but no WATTS, no power. In lay non EE terms it is like some drunk fools trying to push or pull a car; from the side the doors are on.<BR><br>Watt Seconds has been used for Xenon strobes for many many decades. The capacitance of the cap is measured, the DC voltage is measured too; and the 1/2 CV**2 equation cranked. Watt seconds to actual USEFULL light output on your subject has ALOT of variables. With a strobotach for high speed photography, the data is often given for bare bulbs and with say 2 reflectors, and for firing rate of the strobe, temperature of the bulb, bulb age etc. There is no exact conversion of 400 watt seconds to Guide number. My neighbors 400 cc motorcycle is also a HELL of alot quicker in the 1/4 mile than my 400cc riding mower.