new type of fluorescent tube

[mr_big]

any one ever heard of the new sylvania pentron bulbs I have seen these before they look like the small lantern tubes only they are full size are they any different then regular tubes if so I would like to know the difference

[pSlawinski]

1) They are smaller.
2) They are more efficient.
3) They run hotter.
4)  The lamp is brighter.

http://www.sylvania.com/ConsumerProducts/LightingForHome/Products/BulbType/Fluorescent/Pentron/
http://www.sylvania.com/AboutUs/PressAndNews/FeatureStories/RT5withlithonia.htm

[Mónico González]

It's a well known phenomenon that stretching the tube diameter, efficiency are increased, mainly because the arc runs at a higher voltage and lower current, two favorable conditions for a lower percentage of losses due to cathodic fall. Furthermore, a smaller tube diameter helps to minimize the self-absorption of 2537 Angstroms line by the mercury vapour, giving as a result, a greater percentage of energy used to excite the phosphors.
Also, a reduced tube diameter means that the "arc axis" of vapour are closer to glass envelope than in greater tubings, giving as a result that tube walls works at a higher temperature, another favorable condition to increase the Lm/W.
As you have said, these same principle have been sucessfully applied from some years ago to miniature T5 (16 mm) tubes for lanterns and other handheld, car and solar powered applications where the energy consumption can be reduced at a minimum while the efficiency must be regarded or increased. This is specially important at 13w/T5 tubes, so, the great sucess gained by new 13 watts slim-line household (electronically ballasted) fixtures.
If tube lenght increases far away without any variation on tubing diameter and current remains the same, arc voltage must be raised almost lineally to preserve the potential gradient, regarding a close and quasi-proportionally ratio with its lenght, so, the efficiency grows much more. But I guess: where the limit is?
Another attempts have been done with smaller tube diameters, as did Osram some years ago with their FM lamps, which has a tubing as thin as 7 mm.
Any further information on this topic will be welcome.

Regards.
M. Gonz?lez.

[Max]

Hello,

Also, a reduced tube diameter means that the "arc axis" of vapour are closer to glass envelope than in greater tubings, giving as a result that tube walls works at a higher temperature, another favorable condition to increase the Lm/W.

That is not necessarily true. In standard lamps, the optimum of efficacy is reached for a cold spot temperature of 40C. Should the lamp have a lower or greater temperature, the lm/W would necessarily decrease. This is quite a problem in T5 lamps, because the high power density leads to walls that well exceed the 40C peak. As a countermeasure, one electrode stem was made longer than the other one; this way there is one location in the lamp (behind the longest electrode stem) where the temperature is about 40C. This location is recognizable by the condensed mercury.

As you have said, these same principle have been sucessfully applied from some years ago to miniature T5 (16 mm) tubes for lanterns and other handheld, car and solar powered applications where the energy consumption can be reduced at a minimum while the efficiency must be regarded or increased.

Not really in fact. These miniatures T5 exist since the 1950's and have a much lower efficacy that their T12 counterparts. The reason? The ratio between the electrode losses and the dissipated power in the positive column, as you properly said, but most importantly due to the nature of the fluorescent powder employed in the lamps. Today, those small 4, 6, 8 and 13W lamps still employ a binary mixture of halophosphates which, first of all, do not convert efficiently UV in to visible, and secondly, do not resist to high power loadings. Also, as you decrease the tube diameter, the flux of impinging mercuy ions increases and lead to rapid phosphor degradation -? a case particularly true with halophosphate materials.

What permitted de making of high-power / high-efficiency T5 lamps was aq different phosphor and the development of coatings protecting the phosphor from the mercury plasma. Also, some design changes concering the electrode symmetry (i.e. cold spot) and electrodes themselves (i.e. end blackening) had to be made.
Finally, if a given discharge is efficient for a large tube diameter, the efficiency will not necessarily increase as the tube diameter is reduced. The reason is that the energy balance of the discharge depends primarily on the ratio between surface area to volume. Hence, going from T8 to T5 required a change in the buffer pressure and maybe nature of gas in order to reach the best energy balance in the discharge. I am not aware that such measure was ever taken in those small lamtern fluorescent lamps, where the buffer is certainly the exact same as in T12 lamps.
So, in all, the modern T5 lamp is not just a merely longer version of these small coolwhite lamps found in camping lights.

Best regards

Max

[LEE NEWTON]

As a matter of fact the standard T5 lamps (4,6,8,13w) vary enormously in efficacy and lumen maintenance between manufacturers.

As a collector of the 8w size this has been studied in some detail. The European brands who continue to manufacture under controlled conditions (Osram in Italy, Sylvania in UK/Germany) have improved the lumen maintenance of halophosphate - particularly White 530 - by incorporating a small amount of the red banded triphosphor to upgrade the product. I have detected this since 1999. Where 310lumens was quite standard in the 1970s for these, 400lm is now the norm.

Impurities found in some of the cheaper Chinese brands (notably those of little known origin, usually unbranded with the legend etched INTERNALLY) appear to cause rapid degradation such that a lamp may appear to be faulty.

The standard T5s can work comparatively well alongside "long T5" when driven on electronic ballasts. It is this fact which has influenced the manufacturers and importers of luminaires for the 8w and 13w types here in the UK to now incorporate electronic hgh frequency circuits, even on domestic fittings.

Philips appear to have ceased Dutch standard T5 production which is a shame as they were amongst the better performers. They now supply a Chinese product identical to that used by GE, but re-badged, which is not only inconsistent in lumen maintenance, but often of substantially shorter life.

Crompton have enlisted a factory in China, however, that is continuously improving its lamps. Initial findings are that lumen maintenance has improved substantially over a manufacturing period of the last 2 years.