Electron Stimulated Luminescence (ESL) lighting is an interesting alternative to compact fluorescent lights. It is a bit less energy efficient that a good CFL (but far better than an incandescent, like a CFL)**, and its expected lifespan is only about 2/3 that of a CFL, but it has a better color-rendering index (CRI), which addresses one of the biggest complaints many people have about CFLs.

About a month ago, I received a sample ESL bulb from Vu1, the company which has brought these bulbs out, and I have been trying it out in my (basement) office space since then. This bulb is meant as a replacement for a 65 watt incandescent R-30 bulb and, like CFLs, it has a standard screw base to allow it to be used to replace other kinds of bulbs.

My first impression of the light, as soon as I first turned it on, was that it was producing incredibly even illumination. Since then, I have found that this is explained by the company as being “a lightbulb that operates as a Lambert Radiator, meaning the light appears brighter than the Lumens would indicate approaching Lambertian perfection.” It’s a subtle quality of the light, but it’s something I noticed immediately, and that some clients of mine noticed, as well, when I took the bulb to show them for a demonstration.

The CRI of the Vu1 bulb is rated at 90+, which makes it better than most CFLs (which tend to have a CRI around 80), but not quite that of an incandescent (which has a CRI of 100).

As a replacement for an overhead CFL, for my purposes, I like the Vu1 bulb very much. The bulb is directional, with the majority of the light directed downward. The unfinished ceiling of the space is not as lit up as it used to be (which was not a very efficient way to light the space, anyhow), and the work surface is as well lit as before. The increased CRI is subtle; the difference in color temperature between the CFL I had and the Vu1 is the more dramatic change in the space.

(I should note that I have mixed lighting in my office space. When I first tried out the Vu1 bulb, I turned off the other lights in order to judge it by itself. But typically I have a strip fluorescent fixture with daylight color balanced tubes, as well as the Vu1 bulb.)

The Vu1 ESL bulb is also mercury-free, which is one of the company’s major selling points with the bulb. While I appreciate not having any mercury in the bulb, I’m not a mercury alarmist, and I have most of the light fixtures throughout my house fitted with CFLs. The bulb I replaced with the Vu1 bulb was a CFL.

The bulb is surprisingly heavy. The bulb is a vaccuum tube, much like an old television or CRT, and it has a similarly robust envelope. It also works in essentially the same manner as a CRT, using electrons to stimulate a phosphor coated front surface, which glows to produce the illumination (which is why the bulb is best as a directional downlight, rather than as a wide-area illuminator).

My impression is that the Vu1 bulb is best suited for directional uses, like ceiling mounted downlights, rather than for wide area illumination such as table lamps. It is also advertised as being dimmable with a standard dimmer, though I haven’t tried that out yet.

Reviewers like Lloyd Alter at Treehugger and Tristan Roberts at Building Green have criticized the bulb on various counts. I think some of the criticisms levelled at the ESL are reminiscent of those against the CFL. Early CFLs were expensive, but production has ramped up enormously, and they are now available at very low prices.

ESL suffers from being the second incandescent replacement technology to come along. A lot of the investment and development that might have gone into ramping up the ESL has already been spent in developing production and markets for CFLs, and I think that CFLs will (or already have) become as entrenched and difficult to overcome as the incandescents that preceded the ESL. And, at the same time, LEDs are improving in quality and decreasing in cost. With other alternatives out there, and the shifting cost/quality/efficacy landscape, the ESL has a tough road if it is going to become the predominant replacement for the incandescent; I think it’s too late into the game and not enough benefit. But I think there are uses where it will fit in, and it could well develop a niche for itself.

Street pricing for the Vu1 is about $15 (for now*). That’s more expensive than a CFL these days, but that’s in the range of what CFLs were a decade ago. I don’t know if ESL bulbs will see a similar trajectory with price as CFLs experienced. If the Vu1 bulb reaches a point where it is not several times as expensive as the alternative, there may be a real market for the better quality light.

For now, I’m keeping the ESL bulb in my office instead of putting back the CFL. I plan on showing it to other clients of mine on upcoming projects as an alternative to CFL downlights.

[Disclaimer: Vu1 provided the sample bulb to me at no charge for my review.]

[* 15 Feb - Edit to add: After posting this yesterday, I got a call from William Smith, the chairman of Vu1. One thing he wanted to emphasize is that the company expects the price for this bulb to be less than $10 within 18 months, as production ramps up and they start making their own electronics for the bulb and so forth. This isn't going to match the cheap, commodity CFLs in price, but it's certainly in the range of other dimmable bulbs (as another commenter also pointed out). They are also going to have A19 version (more of a standard bulb) coming out later this year, which I'm looking forward to seeing, as well.]

[**19 Feb - first paragraph edited for clarity to add the words "a bit" and insert the parenthetical comment.]