They had some quality control problems with their first bulbs with bulbs burning out prematurely, but they have since fixed it and have made a lot of other improvements to the bulb and have inked a manufacturing deal with another manufacturer, a company call Huayi out of China. Huayi is the same company that did the lighting for China's Olympic Stadium, often referred to as the Bird's Nest. Previously, Vu1 was manufacturing their own bulbs at their plant in the Czech Republic.
Well there goes some of my motive to support the company - repurposing a CRT plant in Eastern Europe for the manufacture of these things. Yet another win for the Chinese I suppose...
They also have the highest Power Factor of any of the new lighting technologies coming in at >.99. This distinction from other lighting technologies actually makes Vu1's bulbs more energy efficient than the lumens to wattage ratio may suggest. 1.0 is a perfect power factor. Anything below that costs utility companies energy. So not only does a lower power factor waste energy, but the cost to the utility company is ultimately passed on to the consumer.
This is true of any non-resistive load. What I've yet to see is any real numbers on what the actual power factor is on CFL and LED bulbs. Whether it is so low as to negate the ~4x efficiency improvement that even cheap CFL's and LED bulbs offer over incandescent has yet to be shown.
It's my understanding that this technology is based somewhat on CRT's. I find it unlikely that they have achieved such a high power factor since high voltage and high frequency switching are required for regular CRT's - not exactly convenient to keeping your device's power return neatly aligned with the grid's delivery (unless additional power factor correction is built into the unit).
I'm not a lighting technician, but I was told by the folks at Vu1 that measuring ESL's "brightness" in lumens is as insufficient as measuring LEDs in watts. The new bulbs are rated at 500 lumens. That doesn't sound very bright, but the bulbs that I own were actually brighter than a 65 watt incandescent. (Perhaps the incandescent would have been equally as bright if it, too, was brand new like the ESL I compared them with.) But the ESL was clearly as bright as a 65 watt incandescent. I realize there are different ways of defining "brightness", which is why I stated that I'm not a lighting technician. This same discrepancy may help to explain how an LED bulb rated at 800 lumens is only as bright as a 40 watt incandescent.
Lumens are one of the better ways of measuring the output of a general-purpose lighting device since the lumen integrates the output of a device over the useful visible spectrum and comes up with a repeatable value. Combine that with other common lighting measurements such as CRI (Color Rendering Index) and CCT (Correlated Color Temperature) and you immediately know a lot about a light source. Take lumens, divide by input wattage, and you get a general measurement of the device's efficiency
as a light source in terms of lumens-per-watt.
Of course, total output is a different measure from intensity in a particular region. If I recall correctly, the simple definition of a lumen is a uniform 1 candella of output over the entirety of a sphere. More technically, a lumen is 1 candella per steradian over a sphere (there being 4*Pi steradians per sphere). So a directional light source producing 12-some-odd candella over a single steradian is the same as an omni-directional one producing a single candella over an entire sphere.
Intensity is a somewhat useful measurement for highly directional sources since one is typically quite interested in light within specific regions for flashlights, streetlights, outdoor floodlights, vehicle headlights within standardized reflectors, etc. It's less meaningful for general lighting applications where the fixture handles the distribution or the distribution is fairly general. Flashlight manufacturers have certainly used a number of widely varying performance metrics - somewhat useful peak beam candlepower in spotlights (typically inflated by huge factors), vague candlepower ratings for general-purpose flashlights, meaningless radiated power ratings (makes monochromatic undesirable narrow-spectrum or monochromatic light sources seem more efficient), and wildly varying "brightness ratings" with no meaning outside the manufacturer's product lineup.
Comparing the ESL lights - being designed for recessed usage, which are fairly directional in their output - to an A19 bulb which radiates in a fairly spherical pattern (and loses a great deal of its output within a recessed or flood fixture) isn't a good comparison. Comparing them to any other indoor floodlight with a similar pattern is.
Every CFL or LED I've seen from a reputable manufacturer that claims to be as bright as an X-watt incandescent has lived up to its promise as best I can tell without photometry equipment to know for sure.
I can see ESL's have some advantage in the sense that the light is radiated at the surface and (presumably) is almost completely radiated outward away from the phosphor screen, avoiding some of the reflector penalties that incandescent, CFL, and LED floodlights pay.