BULB DISCUSSION BOARDS > Modern Electric Lighting

Power Groove fluorescent tubes

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Ed Covington:
The POWERGROOVE fluorescent lamp first appeared in 1956. It was developed by Eugene Lemmers and John Aicher at Nela Park, the lighting headquarters of GE, in E. Cleveland, Ohio.

Max:
Hi All,

     quote:Originally posted by M?nico Gonz?lez:

The main purpose to mould these enigmatic holes onto the glass wall was primarily intended to obtain an assymetrical axial light distribution around the tube, giving two maximum light lobes emerging each one from opposite sides of the tube. So, the light distribution around the tube on a plane that were perpendicular to the axis, are noticeably "eight" shaped.

This is not what I have read on this particular subject, and what would be the benefit of a general lighting lamp with such emission pattern beside a slightly better light control in specially designed optics?

By the 1950's, companies such as GE or Sylvania wanted to make high-power (>80W) fluorescent tubes for large area lighting. The problem to solve was that increasing the power loading of standard F lamps (T12/Argon-mercury filling) had the effect of severely decreasing their efficacy.. so was lost in the process most of the benefits originally attributed to those kind of lamps.
The reasons for this phenomenon are two-fold. First, increasing the lamp power loading increases its cold-spot temperature. So does the partial pressure of mercury in the discharge, which make the medium prone to reabsorbing its own resonance radiation.
The second reason is that increasing the lamp current results in an increased electron density while the electron energy remains quite the same. This leads to an emission of mercury resonant radiation (185 & 254nm) that saturates above a certain dissipated power, which was below the target of these companies at this time.
 
So the solutions to both problems lied in finding a way of keeping the lamp cold-spot around 40C for optimum mercury partial pressure, and an other way of increasing the discharge electron temperature. There were many approaches that depended on the manufacturers ...

GE: found that increasing the surface contact of the mercury-argon discharge with the bulb would increase the electron temperature. Since the tube diameter could not be too large (it would decrease the lamp efficacy due to mercury resonance reabsorption), GE chose to use non-circular cross section tubing, such as already used for LPS lamps.
Crescent-shaped tubes were chosen because they were the least expensive of most designs. It had also the benefit of increasing the discharge path-length for a given lamp dimension, hence the "9 feet of light in a 8 foot lamp" motto. However, this had the inconvenience of increasing the striking voltage of the lamp.
As for the cold spot, the extremities of the crescent cross-section were devoid of plasma (discharge) and were the lamp cold spots.

Sylvania: preferred to choose a different approach as Corning was their supplier of glass tubing. Sylvania did not want to finance Corning's development of non-circular cross section tubing, primarily because of the high cost of these tubes compared to standard tubing, and also because it would pave the way for Corning to sell these kind of tubes to competitors.
So, the solution of Sylvania was to employ a neon-mercury filling instead of the standard argon-mercury mixture. This is the change of buffer gas which led to an increased electron temperature.
This way, they still could commercialise straight HO and VHO lamps. The cold-spot problem was solved with the use of longer electrode stems fitted with thermal shields (metal disks), which shield each lamp extremities from the heat from the discharge.
Anyway, Sylvania offered also crescent-moulded lamps on the market as to offer a "equivalent" of GE's product.

Philips: used almost the same approach as Sylvania's at the exception of the cold-spot. Philips solved this latter problem either with a single dimple in the middle of the lamp, or by fitting a heat sink on the lamp, usually a metal rod affixed to the lamp and the fixture via a spring.

This problem of cold-spot is also recurrent in today's T5 lamps and compact fluorescent. In both case the solution is either the use of mercuyr-indium amalgam (introduced by Osram in 1961), longer stem length, or bulb appendices away from the plasma (like in Philips PL lamps).
 
Worth of mention, is that an alternative way of increasing the electron temperature was found in approximately the same time HO and VHO lamps were developped. The use of standard lamps filled with glass wool (called "recombination structure" because ions and electrons recombine there) increases tremendously the surface contact between the discharge and a "wall". As you might guess, this solution was never put on the market due to manufacturing problems.

Best regards

Max

[This message has been edited by Max (edited January 14, 2004).]

Stan:
Max is right with "cold spot", but is one reason again. Optimal dimensions for greatest luminous flux is, if the tube is "obling cross-section" 1:3. But it is very difficult technologicaly and the air pressure around is very inequaly, was selected this cross-section. Power Groove was made also for much more lower wattage than 215 watts. Many years ago I saw a sample of POWER GROOVE with EXTERNAL phosphor (red lighting organic composition eosine or fuchsine- the base of red inks!), giving deluxe slight pink color of light.
Stan

Max:
Hi Stan!

That's right that a elliptical cross section is simpler than the crescent design, but the force exerted by air along the shorter axis would have prompted for a thick-walled lamps. Actually I find that Power-groove lamps have much thicker walls than T18 tubes used in VHO lamps from other manufacturers.
I also believe there is two other problems which prevented the use of the elliptical design:
-1: its strong heterogeneous light distribution, which would require dedicated optics
-2: a reduced bulb strength which I think would break easily under its own weight if held by only one of its extremities.

quote:Originally posted by Stan:

Many years ago I saw a sample of POWER GROOVE with EXTERNAL phosphor (red lighting organic composition eosine or fuchsine- the base of red inks!), giving deluxe slight pink color of light.

Are you certain it was a fluorescent coating and not just an external coat intended to filter the light generated by the fluorescent layer inside the lamp?
If it was really an external fluorescent coat, it had to stick very well on the lamps, otherwise we would experience a recrudescence of skin cancer LOL


Regards.

Max

Stan:
It was really thin layer of phosphor. I don?t remember, that it was perhaps 30years ago, if it was (e.g.) gelatine layer or so. I know only, that it was originaly from GE, received in inland work Tesla from USA. The sample was losted, never from formerly workers are not able remind it. Moreover if I ment air pressure, I ment difficulties of right-angle cross section. One sample of POWER-GROOVE (broken, part around electrodes and about half meter of tube) in my collection has the wall lucidly more thick than usual fluorescent lamp tube! Stan

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