It has traditionally been hard to beat gas discharge lighting (HMI, MSR) and fluorescent lights (Kino-Flo, etc) in terms of lumens per watt, especially if we want workable color rendering. Both types can achieve 80 to 90lm/W, with LEDs only slightly behind. A low-pressure sodium vapor street light can easily exceed 150lm/W, but of course it’s bright, screaming orange and of scant use in photography. Also, two of the three efficient daylight emitters – LED and fluorescent – are not capable of producing a point source with real punch and throw.
Now, there’s new technology on the horizon – light emitting plasma, which is automatically great because it sounds like a system they’d use on the starship Enterprise. It’s also a pretty unspecific term, because the glowing gas in an HMI or Xenon is also plasma. Usually, though, LEP refers to an electrodeless design, where there is no metal penetrating the quartz envelope containing the plasma, and energy is applied as microwaves. Researchers claim up to 170lm/W of 5300K light with a CRI of 94.
Ok, you have my attention.
The Underlying Technology
There have been related technologies around for a while, mainly involving a glass sphere full of sulfur bombarded with radio waves until it emits light. Efficiency and color rendering are great, but it’s necessary to keep the sphere rotating to avoid hotspots that would cause failure, and it doesn’t work very well below a kilowatt or two. There’s now a slightly more practical design involving a tiny vitreous bubble half an inch long filled with the sort of things you’d find in any metal halide device. Significant advances have been made to make this happen, with some clever thinking involving solid ceramic waveguides to pipe the microwave radiation from the driver electronics into the emitter.
Efficiency approaches twice that of an HMI, with color rendering as good or slightly better, depending on whether you prefer a smooth but lumpy spectral output (HMI) or a jagged but more evenly-distributed one (LEP). Color temperature is about 5300K, drifting to 6100K at 10,000 hours, which as a life-determining factor is many times better than an HMI. It’s flicker free, because most LEP designs use microwave energy at around 900MHz, so it won’t be a problem until you’re shooting any significant fraction of nine hundred million frames per second – only it won’t, because the plasma won’t decay fast enough to pulsate between cycles anyway.
Most current LEP products are fresnels, but presumably, the small light emitting area would make focused beam devices feasible.
Non-Ionizing Radiation
There are two ways to create microwave energy: either with a cavity magnetron, a descendant of World War 2 radar technology that’s found in every microwave oven, or with solid state electronics. The solid state approach is more expensive, but by default a magnetron will produce output modulated with the mains frequency, causing flicker.
The other issue is the need to contain the radio energy. Microwave energy is non-ionizing radiation and cannot give you cancer. However, it can certainly interfere with radio mics, video links, wireless ethernet, bluetooth and cellphones. Since microwave ovens have the same potential and generally don’t cause these problems, the art of shielding this sort of emission is clearly well established.
So that’s the technology.
Hive Lighting (www.hivelighting.com) offers several new products based around Luxim’s 275W LEP device. This would, given normal LEP numbers, equate to a 575W HMI or 1kW tungsten. They have a spacelight, the “Bumblebee 540” at $5,000, with three drivers consuming 825W in total. There’s also a single-emitter fresnel, the “Hornet 180” at $5,600, which competes with things like 575W HMI fresnels. Shipping of the currently-advertised range, plus the “Honeybee” softlight, “Wasp” PAR and “Worker Bee” open-face is estimated for later this year, while a larger 2K fresnel is due in early 2012. The current line use ballasts which are passively cooled and are thus completely silent, and small and light enough to integrate into the lamp head, avoiding an external ballast and head cable.
Brilliantly, they’re also offering a retrofit service, which for $3,200 will take “almost any” 1K or 2K fresnel and put a 275W LEP emitter in it. People have been putting HMI or MSR lamps and ballasts in old tungsten shells for a while, though it’s necessary to replace the fresnel optics to use a conductive-glass version, to allow shielding of radio energy leaked by the LEP emitter, in this case.
The only downside is that the restrike time is up to two minutes. This is less than ideal, given the variable perception of time extant on a film set, and may be tough to fix. HMI and other discharge ballasts capable of hot restrikes do it simply by firing ever higher voltages into the lamp until the gas finally breaks down, and even this is not always completely reliable. LEPs don’t have this option, and it remains to be seen how this works out. Otherwise, they’re fairly price-competitive with HMI, and the consumables are considerably cheaper on a per-hour basis ($500 for 10,000 hours on LEP; probably $200 for 500 hours on HMI) even before you factor in electricity and HVAC costs. Other factors, like robustness and the veracity of those life and color rendering claims, will emerge when people start using them.
I’m not sure about the bee theme, though.
