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view all articles in:
The Reference Room
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Let There Be Lighting: Andy Ciddor
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| Specious Specifications: Works of Fiction |
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| by Andy Ciddor, May 4, 2005 |
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I was recently checking over the list of equipment that a rental company proposed to supply for a project. The rental specification was rather loose, having originated from the production manager, as the LD hadn't started when the spec was written. As the rental company's itinerant lighting consultant, I was asked to review the list to make sure that the equipment they were purchasing and the subhiring for the project would do the job properly.
What I discovered was a mistaken assumption that the model number for a luminaire actually reflected its performance characteristics. Perhaps, when lighting was simply about building and using luminaires to create the best pictures possible, it was acceptable to call a spot "20-35" because its beam varied from 20 to 35 degrees.
However, lighting equipment has become a line of products that require marketing with stylish product brochures and names that evoke power, coolness or technological innovation. As a result, model numbers are just numbers and spec sheets have tended to become works of speculative fiction.
POETIC LICENSING
A couple of years ago when the price of hard disk space became trivial, I ripped my entire CD collection to the hard drive of one of my computers so I could listen to continuous music while I worked.
I also invested in a moderately decent pair of desktop loudspeakers that can output a peak of about 8 W per channel. Up until that time, I had a cheap (sub-$10) pair of powered speakers that were quite adequate for reproducing the squeaks and beeps that let you know that your printer is out of paper or that you have received a new e-mail.
These speakers, which were barely capable of a couple of hundred milliwatts at around 10 percent total harmonic distortion, came in a box that claimed "Total music output 80 W."
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Now, while I realize that the claimed 80 W is the combined power of both channels, I'm utterly bewildered how it's possible to massage a few hundred milliwatts onto a few tens of watts. I have long been aware of that remarkable audio equipment marketing tool, peak momentary performance output, or PMPO. My reading on the definition of PMPO indicates that even this formula is only capable of exaggerating power output by two to 10 times, not the thousands printed on the box.
Although marketing hype in the lighting business has yet to attain these levels of sophistication, a few strategies are still in common use to embellish the capabilities of luminaires. The most prevalent of these is to exaggerate the flood/spot range of the optics, by mixing measurements of beam angle and field angle, through the use of phrases such as "beam size" or "beam range."
FUN WITH NUMBERS
The two commonly used measures of beam size--beam angle and field angle--are clearly and unambiguously defined. Beam angle is the angle that encompasses the part of the beam that varies from peak brightness down to half of the peak brightness. Hence its alternate name, the one-half peak angle. In video terms, this is the area in which the beam varies by up to one f-stop and is seen as the main, bright portion of a luminaire's beam.
Field angle is defined as the angle that encompasses that part of the beam that varies from peak brightness down to one-tenth of that intensity. Unsurprisingly, its alternative title is the one-tenth peak angle. In video term, this covers the area in which the beam varies by approximately 3.3 f-stops and is the majority of the luminaire's beam.
In addition, the beam quality of many luminaires can be tweaked from a "peaky field" setup, where the light is concentrated into a hot spot (used to highlight a particular point of interest in a picture), to a "flat field" setup, where the light is spread as evenly as possible for consistent illumination of a working area.
The marketers' sleight of hand with these numbers involves quoting the narrowest beam angle in peaky configuration as the low number in the beam range, and the widest field angle in flat-field setup as the high number.
Light output figures are another favorite area for information enhancement. Output is often quoted for the luminaire fitted with the brightest lamp that can be shoehorned into the luminaire, even if its objective life, voltage or color temperature makes it impractical for general use.
Light output figures can be enhanced by using terms such as "total lumens" or just "lumens," (which can entail all light coming from the luminaire--including the stuff leaking out of the back), rather than the standard measure of "beam lumens" or "total beam lumens," which measures only that light contained within the half-peak component of the beam.
Thankfully, the marketing of lighting equipment hasn't quite reached the level of nonsense associated with audio products, where terms such as natural, warm, soft, bright, round, digital and analog are wielded with great precision to describe the (possibly nonexistent) differences in sound quality between microphones, compressors, consoles, delays, loudspeakers and even cables, patchbays and batteries.
Nevertheless, a quick look through the equipment catalogs on your shelves or on the Web will reveal that even the most respected brands of luminaires have specification sheets that omit the words "beam angle" or "half-peak angle" from their graphs, or only use "lumens" for the output figures.
While these may turn out to be perfectly innocent omissions, the injunction caveat emptor (let the buyer beware) is at least as important in lighting as anywhere.
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Andy Ciddor has been involved in lighting for more than three decades as a practitioner, teacher and writer.
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