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<blockquote data-quote="WayneF" data-source="post: 533697" data-attributes="member: 12496"><p>The overall energy is computed as watt seconds (like kilowatt hours on our electric bill, just a much larger unit of kilowatts and hours). One watt second is numerically same as one joule of energy, if that helps at all.</p><p></p><p>This energy aspect is computed like this:</p><p></p><p>Continuous light... can only be useful to a camera when the shutter is open.</p><p></p><p>Let's say 85 watts. </p><p></p><p>If a one second shutter, then 85 watts x 1 second = 85 watt seconds of energy.</p><p></p><p>If a 1/200 second shutter, then 85 watts x 1/200 second = 0.42 watt seconds</p><p></p><p></p><p>CFL efficiency might be 4x greater than incandescent (of light output).</p><p></p><p>So let's say 4x85 is 340 watts incandescent.</p><p></p><p>340 watts x 1 second = 340 watt seconds.</p><p></p><p>340 watts x 1/200 second = 1.7 watt seconds.</p><p></p><p>But since fluorescent is about 4x more efficient than incandescent, really, the output of these two are about the same as the CFL. The greater Incandescent watts number merely creates heat instead of light. That's why we say the CFL light is "equivalent" (as 4x incandescent).</p><p></p><p>A regular size (full powered) speedlight flash is typically about 75 watt seconds. A smaller version maybe 60 watt seconds. </p><p></p><p>Watt seconds is about electrical energy input. Output depends on efficiency. Flashes have efficiencies of creating light too, flashes being similarly efficient as fluorescent (both are ionized gas, instead of heated incandescent filaments).</p><p></p><p>For a light bulb, watts is computed as voltage x amps.... which is a rate of power. then muiitplied by seconds for watt seconds of energy.</p><p></p><p>For flash, watt seconds is computed as 1/2 CV², C is flash capacitor capacitance, farads, and V is the charge voltage of the capacitor (electrical input energy).</p><p>A Nikon SB-800 flash is 1400 ufd at 325 volts, or 73.9 watt seconds (there always is a slight tolerance).</p><p></p><p>Making up numbers, but if we imagine the flash duration was 1/1000 second, then this implies 75,000 watts at 1/1000 second duration. Flashes put out a lot of light.</p><p></p><p>So the regular size speedlight flash can be 75 watt seconds, capable of full output at any usable shutter speed, like 1/200 second (because the flash is faster than the shutter... the shutter merely needs to be open). Larger studio flash can be of course much larger.</p><p></p><p>The 85 watt CFL at 1/200 second is maybe 0.4 watt seconds.</p><p></p><p>This is a pretty large difference, almost defying comparison. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile :)" loading="lazy" data-shortname=":)" /> But because the efficiency is similar, the 85 watt CFL could compete with the flash if the bulb used a 1 second shutter speed (the flash duration is still very fast, regardless of how long the shutter is open). To me, this suggests that 200 85 watt CFL bulbs at 1/200 second could compete with the speedlight. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile :)" loading="lazy" data-shortname=":)" /></p><p></p><p></p><p>There are major differences in use. We can see continuous light, to set it up as we like. And the camera can meter continuous light. Neither is true of flash, but we learn to use it, it is not hard.</p></blockquote><p></p>
[QUOTE="WayneF, post: 533697, member: 12496"] The overall energy is computed as watt seconds (like kilowatt hours on our electric bill, just a much larger unit of kilowatts and hours). One watt second is numerically same as one joule of energy, if that helps at all. This energy aspect is computed like this: Continuous light... can only be useful to a camera when the shutter is open. Let's say 85 watts. If a one second shutter, then 85 watts x 1 second = 85 watt seconds of energy. If a 1/200 second shutter, then 85 watts x 1/200 second = 0.42 watt seconds CFL efficiency might be 4x greater than incandescent (of light output). So let's say 4x85 is 340 watts incandescent. 340 watts x 1 second = 340 watt seconds. 340 watts x 1/200 second = 1.7 watt seconds. But since fluorescent is about 4x more efficient than incandescent, really, the output of these two are about the same as the CFL. The greater Incandescent watts number merely creates heat instead of light. That's why we say the CFL light is "equivalent" (as 4x incandescent). A regular size (full powered) speedlight flash is typically about 75 watt seconds. A smaller version maybe 60 watt seconds. Watt seconds is about electrical energy input. Output depends on efficiency. Flashes have efficiencies of creating light too, flashes being similarly efficient as fluorescent (both are ionized gas, instead of heated incandescent filaments). For a light bulb, watts is computed as voltage x amps.... which is a rate of power. then muiitplied by seconds for watt seconds of energy. For flash, watt seconds is computed as 1/2 CV², C is flash capacitor capacitance, farads, and V is the charge voltage of the capacitor (electrical input energy). A Nikon SB-800 flash is 1400 ufd at 325 volts, or 73.9 watt seconds (there always is a slight tolerance). Making up numbers, but if we imagine the flash duration was 1/1000 second, then this implies 75,000 watts at 1/1000 second duration. Flashes put out a lot of light. So the regular size speedlight flash can be 75 watt seconds, capable of full output at any usable shutter speed, like 1/200 second (because the flash is faster than the shutter... the shutter merely needs to be open). Larger studio flash can be of course much larger. The 85 watt CFL at 1/200 second is maybe 0.4 watt seconds. This is a pretty large difference, almost defying comparison. :) But because the efficiency is similar, the 85 watt CFL could compete with the flash if the bulb used a 1 second shutter speed (the flash duration is still very fast, regardless of how long the shutter is open). To me, this suggests that 200 85 watt CFL bulbs at 1/200 second could compete with the speedlight. :) There are major differences in use. We can see continuous light, to set it up as we like. And the camera can meter continuous light. Neither is true of flash, but we learn to use it, it is not hard. [/QUOTE]
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