Slim T5 lamps new industry standard
Slim T5 lamps new industry standard
Starting in Europe, Philips and Osram have taken the lead in introducing a new lighting industry standard for fluorescent lamps. Tomorrow's standard fluorescents are likely to be efficient 16-mm diameter T5 lamps, which will replace today's 26-mm T8 lamps in new installations. GE Lighting has followed this trend by introducing the T5 lamps in some of the wattage classes.
The new T5 lamps are designed for operating exclusively with electronic ballasts (dimming will be possible), and the most efficient lamp (35 watt) offers a 10-15% improvement in system efficacy compared with electronically ballasted T8 lamps. All three manufacturers use internal protective shield technology to minimize light depreciation to ~5% over the life of the lamp. This technology has also made it possible to reduce the mercury content of lamps to about 3 mg. Previous lamps typically contained 15 mg. (See Mercury-cut increases efficiency, IAEEL Newsletter 4/94).
NEW DIMENSIONS AND RATINGS
The new lamps reflect industry attempts to radically change lamp dimension standards: they changed the lamp diameter, and the lamp-length standard will no longer be based on multiples of a foot. The length of the lamps has been reduced by 50 mm for each "footage class", so that a standard recessed luminaire can fit exactly within the European standard building module dimensions of 600 and 1200 mm.
Due to their shorter lengths and higher efficiencies, the new lamps are offered in new wattage packages. Both Philips' and Osram's product lines will have lamps with 14-, 21-, 28-, and 35-W ratings, whereas GE has chosen to offer 18- and 36-W lamps.
The lumen packages do not correspond exactly with that of the T8 lamps: For instance, a T8 36-W lamp with electronic ballast rated at 3 250 lumens must be compared with the new 28-W lamp with a nominal lumen output of 2900 lumens. The efficacy of the lamp, including ballast, is ~87 lm/W which is about 10% higher than that of the T8 system (~74 lm/W).
The increase in system efficacy has been achieved by optimizing all parts in the lamp- and ballast system. For example, the new lamps are optimized for maximum light output at a more realistic ambient temperature of 35° C, instead of ~25° which is typical for fluorescent lamps. Moreover, the T5 system allows for the higher lamp current that follows as a consequence of combining the more efficient argon filling and the thinner lamp diameter.
APPLYING T5 LAMPS
Manufacturers argue that the new T5 system can further improve the efficiency of a new lighting installation based on their claim that the new lumen packages better reflect current room size and illumination standards. However, this is a questionable argument. If, for instance, an open office solution is chosen as an example where the luminaires simply produce uniform light levels, it is easy to reach a very high installation efficacy. But when dealing with rooms for one or two persons, the installed power will depend on how well the room size and lumen package match.
Still, due to the small diameter of the lamps, reflector designs can be developed that are more efficient than those used with T8 lamps. This will likely add to the total system efficacy; however, the extent of the improvement will depend on the skill of the luminaire manufacturers. It should be noted that some lighting designers have raised a warning flag: The new lamps are much brighter than the older ones, their surface luminance ranging somewhere between that of an efficient compact fluorescent lamp and those of the T8 lamps; thus there is a risk that glare problems will increase. In cases where the new lamps are used for direct lighting, demands on luminaire designers will be high, especially if luminaires are made very shallow.
The small lamp diameter also allows more compact luminaires to be used. In a quite optimistic sales pitch by lamp manufacturers, the compact size is claimed to help reduce the space needed between the ceiling and the floor of the next story in new office buildings, thus allowing structures to be built more compactly.
Although luminaire manufacturers don't seem to be too impressed with the "more-floors-per-building" argument, they do point out that more compact luminaires should help reduce the costs of new lighting systems. The new electronic ballasts for these lamps are also more compact than previous ballast models.
At least one manufacturer (Philips) has designed its new T5 ballasts to extend from 30MHz to 1000 MHz for radiated interference; this enables the ballast to be used in areas where sensitive electrical apparatus, such as medical or communications equipment, is located.
Will the lamp succeed on the market? A large number of European luminaire manufacturers presented new luminaires for the lamp at the Hannover lighting fair, so the lamp seems to be here to stay.
Nils Borg