Paul C. Buff, Inc. Technical Forum

I apologize in advance for posting this because I am sure it must have been discussed before on this forum, but at the same time, after trying, I have been unable to find that discussion.

The Paul C Buff interview on Studiolighting.net (http://www.studiolighting.net/studio-ph ... episode-1/) was great and my wife and I listened to it three times. But in one section, Paul likens a one-second 600 watt hot light exposure to a 600 watt second strobe. While I realize the point he was trying to make, my question goes to the point of further clarifying the efficiency issue.

Some of the energy in a watt-second, coulomb-volt, or joule, is transformed into light and some of is transformed into heat. In a xenon flash tube, while the temperature of the gas is raised to megadegrees momemtarily, I would think the specific heat is relatively low so that the proportion of light producing energy is equal to or greater than that of heat producing energy. In an incandescent or halogen lamp, on the other hand, I would think that the balance is shifted far more toward the generation of heat; "More heat than light", as the old saying goes.

While Paul C Buff does discuss the issue of efficiency in his truly fascinating interview, I am left wondering if somehow I might be missing something due to his comparison of a 600 watt bulb for one second with a 600 Ws Alien Bee lamp for 1/1000 second.

Again, I apologize for posting this as I am sure it has been discussed before; I just couldn't find it conveniently.

Let me refine this. A typical tungsten lamp produces 15 to 20 lumens per watt (lumens being light). Well designed monoflash units produce from 40 to 45 Lumenseconds per wattseconds. Thus the flash is a little better that twice as efficient in converting electrical energy to visible light (more light/less heat).

Now, if the voltage on the tungsten lamp is raised such that it burns "hotter" and approaches the 5600°K range of the flash, it's efficiency will approach the same 40-45 Lumens per watt range, but the bulb will burn out in a matter of seconds. This is why high power video and projector lamps produce on the order of 3200 - 3400°K and burn out in 3 to 50 hours and achieve efficiencies on the order of up to 25-28 lumens per watt . . . more light, less heat, shorter burn life. If a replacement could be found for the tungsten filiament . . . one that could tolerate say 5600°K temperatures without disintegrating, highly efficient filament lamps would be practical.

So in reality, it would take about 1200 watts of typical tungsten light exposed at 1 second to equal the exposure value of a single 600WS flash. If the flash duration is 1/1000 second, the actual instantaneous intensity of the flash is on the order of 2000 times the intensity of the incandescent for an equal W/WS input. Shorter duration flash units produce even higher peak intensities for a shorter period of time - hence better action stopping.

Luap:

Upon reflection, this makes sense -- the closer one would get to literally vaporizing a filament, the more light and the less heat loss. Practically speaking, the gap won't likely soon be breached.

Any thoughts on the photographic potential of LED technology where lumens (light) per watt levels are much higher as long as heat dissipation can be mananaged (e.g., pipes)?

PS - Thanks so much for the wonderful products (-: ;-)

Jabberwocky

LEDs are absolutely the light source of the future, but we have a few years to go yet. The 200 lumens per watt threshold has already been crossed, but these are entirely too expensive to be commercially practical at this point. Commercial LEDs are achieving 35 to 55 lumens per watt. But unlike tungsten lamps, the LEDs cannot withstand the heat they generate at reasonable illumination levels for photography. At 50 lpw it takes about 40W of heat dissipation to equal a 100W tungsten. 40 watts in a concentrated are the size of a modeling lamp requires heat sinks and fan cooling to keep the LEDs in their maximum 125°C operating range. And the cost is waaaaay higher than incandescents.

To me, compact fluorescent is a dead end technology for many reasons.