new "Electron Stimiluted Luminescence" light bulb technology

[Anders Hoveland]

ESL is an acronym for "Electron Stimulated Luminescence". Although the technology is basically the same as the old cathode-ray televission tubes, it is a new technology in the sense that it has never been applied to general lighting purposes before. Right now there is only one version of this new bulb available, a directional 65-Watt equivalent. The price is 15 dollars each.
 
The quality of light from this new bulb is claimed to be better than that from both fluorescent and common white LED's, although still not quite as good as halogen incandescents. Here is a spectral graph of the wavelength distribution from this type of light source:




One of the major selling points of the ESL bulbs are that it does not contain any mercury, and so its improper disposal does not lead to any environmental hazard.

The other major claimed advantage of ESL better quality of light, better than standard LEDs. They can also achieve a CRI of 90+. If you compare current price differences between ESL and high CRI LEDs, a strong financial argument can be made in favor of ESL.

Another plus, ESL bulbs are also fully dimmable. A dimmable CFL is typically substantially more expensive than a regular CFL, so this helps narrow the price difference.

I hope the ESL technology has not entered the market too late. While ESL's have their own unique advantages, it is really sort of a specialty niche. The CFL technology has already been more developed, and LED's have already come into mass production. The ESL's may be squeezed out of the market by the other available technologies, since they were developed first.

 The problem is that these first ESL bulbs consume just slightly more power than CFL's. If someone wants "efficiency", they are more likely to go with CFL's, where as if someone wants quality of light they are more likely to go with incandescent bulbs. Few people will be willing to pay more for bulbs that are almost as efficient as CFL and have almost the good quality of light as incandescents, especially when LED's are available that are both much more efficient and have a quality of light somewhere between CFL's and ESL's. Although, like I mentioned, ESL's do not cost much more than dimmable CFL's, so if ESL's make sense anywhere, they would best replace dimmable CFL floodlights. The problem is most consumers do not think about all the subtle advantages and disadvantages of lighting, and are unaware what the optimal choices are for each particular situation. From what I have seen, most people do not like to think very much when buying light bulbs. The vast array of different lighting options now available has mostly resulted in consumer confusion. Most consumers only care about two things: initial price and light output. That is, until they get home and realise they are not happy with the new lights.



 I want to emphasise the ESL's are still the best choice of technology in certain very specific situations.

 1. If you want increased efficiency but still want a quality of light better than CFL's or current LED's

 2. If you want more efficient lighting, the UV radiation from CFL's is a concern, but you do not want to pay the higher initial price for LED's
 (or perhaps you are concerned that someone may steal the more expensive LED)

 3. If you are one of those people that are irrationally obsessed with the environment and do not want to buy an energy efficient bulb that contains mercury, but you need a retrofit bulb that can go into an enclosed fixture and are concerned about the higher power LED not functioning well because of overheating.


In terms of ideas to increase efficiency, I think the efficiency of an ESL lamp could be significantly raised if it used red LED emitters instead of the europium phosphor. I am not sure how practical this would be in terms of added cost, but the red LED chips could be located behind the glass vacuum housing and shine through behind the phosphor screen, which would act as a diffusor, evenly mixing the light.

Again, I am not really sure how much the incorporation of red LED chips would raise the cost of an ESL, but I think it could be a major selling point to "environmentally conscious" consumers if they could get the efficiency even slightly above CFLs. From a marketing perspective: better than CFL, lower cost than LED but better light. A regular 60 watt equivalent LED retrofit downlight sells for 25 dollars and is not even dimmable. I think an ESL with some low-power (1-2 w) red LED enhancement could be sold for a similar price or slightly less than this.


http://www.mnn.com/your-home/at-home/blogs/the-esl-a-light-bulb-that-speaks-the-language-of-energy-efficiency

http://www.greenprophet.com/2012/03/esl-cfl-mercury-lights/


Spiral Compact Fluorescent (CFL) bulbs typically do not last as long as they claim, and that seriously undermines the argument that they have a net benefit for the environment. The ESL has a rated lifespan of lifespan of 11,000 hour, longer than most CFL's (most CFL's have rated lifespans of 5000-6000 hours, but a consumer report found the average much lower, around 3000 hours under realistic operating conditions)
http://www.freerepublic.com/focus/f-news/2833134/posts

Here is site explaining why CFL's are actually worse for the environment, despite all that is claimed:
http://www.greenmuze.com/blogs/guest-bloggers/1031-the-dark-side-of-cfls.html



Here's a review of the ESL bulb:

The bulb is a little heavy, but not extremely so. Considering it is basically a big glass vacuum tube and has to contain a 5000 volt power supply, it is fairly light.
 When it is first turned on there is definitely electrostatic charge that builds up on the surface, just like the old cathode ray TV screens. The glass can get really hot if left on for a long time.

The light feels somewhat similar to fluorescent or CFL, and has a pinkish tint? though without the unpleasant purplish cast characteristic of fluorescent. I looked at the light through a diffraction grating (a CD) and there is a strong orangish-red line, a broad band of coverage from green to blue, but there is also a distinct green line overlapping this. (There seems to be very little yellow light in the spectrum)

 Skin tones look okay, but a little more orange colored than natural. Skin tones do not look the most vibrant, but they are not greyish dead either. Somewhere between a low CRI LED and a high CRI LED, if that gives some reference comparison. The illumination feels "hollow" and washes over everything, not "filling" and warm. Blue color rendering is good though, blue objects are not all rendered deep royal blue/indigo like they are under LED. Plenty of soft dull blues and greenish-blues.

 You know what the light really reminds me of ? Ceramic metal halide (CMH). And I say this as a complement. Ceramic metal halide is used in high end department stores, I'm not talking about ordinary metal halide here.

The light from ESL bulbs feels like a three-way mix between incandescent, CFL, and CMH, that's the best way I can describe it.

The ESL bulbs do not appear to have any flicker, which is an issue for many CFL and some cheap LED bulbs.

It's difficult to describe the quality of a light source if you have not seen it yourself. Paradoxically, although in one way the light from the ESL feels like the ghastly unnatural glow of a CFL, in another way the quality of light feels very "natural". Or at least high definition. The illumination feels "real", and not "digital" like LED light feels. The light also feels just a little harsher (on my eyes at least), however I doubt the light from a 3200K halogen would be all that different (3200K halogen is not commonly encountered because the filament lifespan is much shorter)

Here's another review:
https://psproefrock.wordpress.com/2012/02/14/review-of-the-vu1-esl-light-bulb/

[Anders Hoveland]

If I can note one more thing about these ESL bulbs, the light they emit is indeed very diffuse. Much more diffuse than a comparable LED flood, even one covered with a frosted plastic diffusor (Those opaque plastic covers over LED bulbs seem to only diffuse some of the light, most of the LED light seems to go right through without changing direction much from its narrow beam angle, there is still a lot of glare if you stare directly into the LED). ESL bulbs definitely do not produce a "beam" of light. The diffuse nature of light coming from the surface of the ESL is very comparable to the diffuse distribution light from a fluorescent tube, not really surprising considering they are basically both glass tubes coated with fluorescent phosphor. I can definitely see what they meant by "Lambertian light distribution". This is another big difference with LED floods on the market, the light distribution, which could potentially be either a good thing or bad thing, depending on the situation.

The thing I notice about almost all LED flood lamps that have frosted plastic diffusor covers is that most of the light still tends to be very directional. It is as if the plastic diffusor cover simply skews the path of each light ray just enough so that the inside is not clearly transparent. But the beam of light from the LED emitters inside is still basically traveling in the same general direction. It's not truly diffuse. Looking directly at the surface of the bulb from the front end, there is a high level of glare, but viewing the surface from the side the glare is much less. Only a fraction of the light is actually being diffused, most of it is traveling straight through the plastic cover. Even frosted incandescent PAR lamps are not like this. If you need a bulb for recessed ceiling fixtures, and you do not want all the light pointing directly straight down, the Vu1 bulb is a great option here.

 It's not "omnidirectional", but it does send light in all directions from a flat surface. This is a unique effect, inherent to ESL technology.

 I suppose it would be possible for LED bulbs to achieve this too, but it would require a very heavy degree of diffusion, and in practice few of them do this because it would result in a substantial decrease in light output efficiency.
 I also think frosted glass does a much better job of light diffusion than opaque plastic, one can see the difference between a Cree glass globe LED bulb and a regular plastic globed LED bulb, for example.

Do these CRT bulbs make a high-pitched sound like full-sized CRT TVs?

The bulbs do not emit any noise. I was listening very carefully and could not hear anything. The only noise whatsoever is a tiny bit of static discharge/crackling on the glass when the bulb is first turned on, and then the interior filament jingles just a little when the bulb is turned off. It's not even audible unless your ear was right up against it. I am really sensitive at hearing low-level noises, and there was no high-pitch sound or any humming.

the real question is... Does it flicker?

 If it works like a CRT then it probably flickers...

There is absolutely no flicker either, and this has to do with the nature of the technology. The Cockcroft-Walton multiplier (which is a series of capacitors and diodes) empties into a cathode ray vacuum tube. There is an inherent limit to how much current can pass through the vacuum, from the cathode to anode collector grid, at any one time. Because free electrons are naturally repulsive to eachother, and a vacuum is not a true conductor, so the current density is low. It's almost equivalent to a capacitor emptying through a resistor, very gradual. When the tube is turned off, it quickly fades out, just like an incandescent bulb, which indicates that when the power is cut, the cathode ray probably continues to discharge at full current for a fraction of a second afterwards, eliminating any flicker. CRT televisions do have some flicker, but only because the cathode ray is in the form of a focused beam that sweeps across the screen. In the Vu1 tube, the cathode ray is not focused and does not sweep back and forth across the screen.

What about the start up time?

They are not slow to start up, it is just that they do not suddenly flash on. When the ESL lamp is first turned on, the center lights up first, as the cathode beam expands, and the glow moves outwards. Within 1 second after being switched on, they put out plenty of light. It takes about 2? seconds for them to reach full light output. It's a unique effect, and I kind of like it actually. It gives your eyes just a second to adjust when you switch on the lights. And reading through the reviews, several other people commented the exact same thing.

 The effect is really nothing like CFL bulbs. When you turn on a CFL bulb, it suddenly comes on, but initially is rather dim (about 30% of light output). Then it takes another 20-40 seconds to reach full light output. This is really frustrating to many consumers when they are walking down the hall, flip on the light switch, and there is not enough light to see.
 [/quote]

How is the light quality?

One thing I've observed though, the light output from these really *is* quite pleasant in ways that I can't quite stick my finger on. That's the main draw of these bulbs: the different quality of light.
 I'm not saying the color rendering looks perfectly natural, but there is something pleasant about the light (or at least more "pleasant" than CFL or LED). That's why I compared it to ceramic metal halide, if you have ever taken the time to notice them in high end department stores. Seems very sharp and high definition. Or maybe I should say the light seems like some sort of hybrid between CFL, ceramic metal halide, and incandescent all mixed together.

What about the color rendering?

The color rendering of the Vu1 bulb to me seems to be at a similar level to a Cree TrueWhite LED fixture (92 CRI). Unlike under LED lighting, the Vu1 bulb has really good blue color rendering. I have a tie with two colors of blue. Under the LED lighting both colors look like the same hue of blue, just different shades, but under the Vu1 bulb one of the blues looks more azure-colored, contrasting to the dark royal indigo of the other color. It's not a huge noticeable difference, but I think it looks better.

Does anybody know what phosphors are used in the ESL bulb?

I believe the "electron stimulated luminescence" phosphor is Zinc Sulfide (ZnS) based, with some Europium (to achieve the reddish-orange spectral line). Basically not that different from regular cathode ray tubes like your old TV. However, I believe in the latest run of bulbs Vu1 has also added terbium phosphor, at least judging from the spectral lines I am seeing through a diffraction grating. Tri-color fluorescent tubes also use these same rare earth Europium and Terbium phosphors.

Also to clarify, the zinc sulfide phosphor they are using is probably ZnS:Ag, doped with silver (in the form of silver sulfide, to be exact, I think). This is the most efficient of the ZnS phosphors, and emits a blue color. I believe the first version of the Vu1 bulb used a green/yellow ZnS phosphor too, but the use of terbium phosphor in the second version of the Vu1 bulb made this unnecessary. I say this because what I actually see through a diffraction grating does not match up with the spectral graph originally provided by Vu1, they modified their phosphor composition somewhat.

If this bulb makes very good light with the phosphors, couldn't a CFL make good light with the same phosphors too?  

That is a good question, and the answer is yes and no. I am not an expert in phosphors, but I do not think zinc sulfide phosphors can be used in fluorescent tubes. Or they may degrade much faster. And I suspect the efficiency of getting zinc sulfide to glow using UV radiation may be substantially lower than using cathode rays, but I could be wrong here. Another important factor is the prominent 436nm blue-violet line emitted from mercury discharge, this constitutes a substantial part of the spectrum from a fluorescent tube.

 To make matters more complex, there are different types of phosphor compositions being used in some fluorescent tubes. Standard tri-color fluorescent tubes only use europium and terbium phosphors, which primarily emit at 611nm and 546nm, respectively, with a smaller bluish-cyan peak at 490nm from the terbium. A few special fluorescent tubes use a slightly different blend of phosphors, employing a phosphor that has wide spectral coverage in the blue-green part of the spectrum, unfortunately I am not sure what the chemical composition of this particular phosphor is. The spectrum of this type of fluorescent phosphor blend does appear very similar to the ESL phosphors (what I can see through a diffraction grating held up to a Vu1 bulb). However, there is still a very prominent 436nm and 405nm mercury lines, and that limits how much blue-green phosphor can be used. So I would still say that the spectrum of light from ESL is superior because it does not contain those mercury lines.

[Chris W. Millinship]

Edit from Anders Hoveland: I am very sorry, I accidentally modified your post  
And I do not know how to bring it back. Could you please retype it here, sorry and thanks.

I did not realize it was possible to modify someone else's post in this forum.

[Anders Hoveland]

The big question from this particular collector is where I can get one from?

http://www.lowes.com/pd_377410-34246-R30-101D_0__?productId=3558760
http://www.destinationlighting.com/item/r30-energy-efficient-light-bulb-watts/346884


You might want to use a voltage converter, I am not sure how the bulb will operate on 230v (european outlet)

[Chris W. Millinship]

Thanks for the info. I have transformers, so unless frequency is important I could light one without problems.

Unfortunately the Lowes link states no longer stocked, and the other one led me all the way to the end of the order process (and wanted to charge me ?60 with shipping, etc - the lamp was only ?12!) only to fail on submission and state "unable to process due to security restrictions". The Paypal option didn`t seem to work either, so I hope my credit card number is now not floating around somewhere it can end up in the wrong hands.

Disappointing, but thanks for your assistance. Maybe one will show up on Ebay or somewhere I can actually buy from in the future, or they might end up being marketed outside of the US.

-

As for the edit thing - paging Tim - what`s that about then? It certainly should not be possible to modify other users posts. Is there a setting that needs to be amended somewhere? I don`t recall exactly what I wrote, but it was basically a big-up for the review, a comment on CFL and LED, and that quoted question on where I could get one of these ESL lamps.