Here are the reasons I chose to purchase the Joker 800 Zoom over the M8...
Jokers are great lights, and have some very innovative accessories. The one drawback to Jokers is that their ballasts are not Power Factor Corrected. Their poor Power Factor causes them to use power inefficiently and the harmonic currents that they generate can have a severe adverse effect on the power waveform of portable generators. Since the poor Power Factor of Jokers is commonly overlooked because of their small size, I would like to take this opportunity to explain it in detail and show how it might impact Matthew’s decision.
If we look at the technical specifications for Joker Buglites, we see that the ballast of the Joker 800 draws 12.5 Amps rather than the 7 Amps you would think using Ohm’s Law (800W/115V=6.956A) This difference is between what is called “Apparent Power” and “True Power.” The ratio of “True Power” to “Apparent Power” is the “Power Factor” of the light. The Joker 800 then has a power factor of .56 (6.956A/12.5A=.556 )
Used on wall outlets, this relatively inefficient use of power is negligible because the power draw of the Joker 800 fits easily in a standard wall circuit. However, the greater Apparent Power of lights with a poor Power Factor must be factored when using portable generators. For instance, you would think that you could operate a Joker 800 on a 1000W. But, in fact, you would overload the generator because the “continuous load” rating of 1000W Generators is typically only 850W and the actual load of the Joker 800 is 1437W (12.5A x 115V = 1437W.)
The greater Apparent Power of Lights with a poor power factor is not the only consideration when operating them on a generator. When you use lights sources like HMIs, Kinos, CLF lamp banks, and even LEDs, on generators it matters not only what type of ballasts the light uses, but also what type of generator you use to power it. The harmonic currents that ballasts with poor Power Factor, like the Joker 800 electronic ballast, draw can have a severe adverse effect on the power waveform of some generators.
Normally, when you plug a HMI, Fluorescent, or LED light into a wall outlet you need not be concerned about the current harmonics generated producing voltage distortion. The impedance of the electrical path from the power plant is so low, the distortion of the original voltage waveform so small (1-3%), and the plant capacity so large, that inherently noisy loads placed upon it will not affect the voltage at the load bus.
Left: Waveform of grid power. Right: Waveform of conventional AVR Generator (Honda EX5500) operating non-linear lighting pkg. consisting of two Arri 1.2kw non-PFC ballasts and a Kino Flo Wall-o-Lite.
However, it is an all together different situation when plugging non-power factor corrected HMI, Fluorescent, or LED ballasts, into conventional portable generators. Given the large sub-transient impedance of conventional generators even a small degree of harmonic noise being fed back into the power stream will result in a large amount of distortion in its’ voltage. Add to that, the fact that the original supply voltage waveform of a conventional generator is appreciably distorted to begin with, and you have a situation where the return of any harmonic currents by an HMI, Fluorescent, or LED ballast will result in significant waveform distortion of the voltage at the power bus (see oscilloscope shots above.) The waveform distortion caused by these harmonic currents can have a severe adverse effect not only the generator, but also other electronic equipment operating on the same power.
The ballast of the Arri M8, on the other hand, has a power factor of .98 (near unity) and so draws less power (approx. 7A) and generates no harmful harmonic currents. When you consider that a Kino Parabeam 400 draws only 4A, the 5.5A difference between the power factor corrected M8 and non-power factor corrected Joker 800 can make a big difference in your production values when using a portable generator.
The poor Power Factor of HMIs, Kinos, CLF lamp banks, and even LEDs, have been vexing set electricians for years. Use this link for an article I wrote for our company newsletter that explains the electrical engineering principles behind these issues and how to resolve them.
This article is cited in the just released 4th Edition of Harry Box's "Set Lighting Technician's Handbook" and featured on the companion website
"Box Book Extras." Of the article Harry Box exclaims:
"Great work!... this is the kind of thing I think very few technician's ever get to see, and as a result many people have absolutely no idea why things stop working."
"Following the prescriptions contained in this article enables the operation of bigger lights, or more smaller lights, on portable generators than has ever been possible before."
The article is available online at http://www.screenlig...generators.html.
Guy Holt, Gaffer, ScreenLight & Grip, Lightng Rental and Sales in Boston