20th Century Inventors:
Compact Fluorescent Lamps

S.I. Negative #99-68, © Philips

Johan B.J. van Overveld and Louis Vrenken (l-r)
testing compact fluorescent lamps at Philips around 1980

"The use of the new phosphors is not restricted to 40W T12 lamps."
-- Louis Vrenken, 1976 paper

Attempts to manufacture a practical compact fluorescent lamp (CFL) date to the beginning of commercial fluorescent technology in the 1930s. A major hurdle lay in the inability of phosphor coatings (materials that convert ultraviolet rays to visible light) to withstand close proximity to the electrical arc in a fluorescent lamp.

Conventional halophosphors, used since the early 1940s, simply would not emit light for more than about 100 hours when placed in a thin tube. While there were other physical and manufacturing difficulties facing CFL designers, the "lumen maintenance problem" seemed especially intractable.

During the early 1960s a new type of phosphor using rare-earths was introduced into the manufacture of color TV tubes. In 1978, Louis Vrenken and his colleagues at Philips (Eindhoven, The Netherlands) discovered that combining the rare-earths with an aluminate host-lattice (rather than the tungstate or silicate used previously) resulted in new phosphors that lasted for thousands of hours in thin tubes -- long enough to be commercially viable.

Philips' SL-18^® lamp, using the new phosphors, became available for purchase in 1980. The 18 watt CFLs with their 1/2" diameter folded tubes represented a radical change from then common 40 watt, 1-1/2" diameter linear tubes. (Fluorescent lamps are classed by diameter in 1/8" increments, so T12 in Vrenken's statement above refers to a Tubular, 12/8" diameter lamp.)

Incandescent lamp engineers use a technique called "force testing" to determine how a filament lamp will age. Increasing the voltage or current accelerates the deterioration of the light emitting filament in a predictable fashion. Fluorescent and other discharge lamps do not behave so predictably and cannot be force tested. To see how much light an experimental CFL will produce after 10,000 hours the lamp must actually burn for 10,000 hours -- over a year. In the photo above, Overveld and Vrenken are checking some of their experimental lamps.