The L-90 magnetic electric guitar pickup was released by Lawrence Sound Research (LSR) in 1976, the precursor to the L-500.

From the ad pictured below "L-90XL  Replacement pickup developed and built in Germany in 1968 by Bill Lawrence and reissued in 1977 ".  I guess Bill developed this while at Lawrence Electro-sound?

Advertisement/photos as they appeared in Guitar Player magazine, July 1979.

Photo of Aerosmiths Joe Perry and Brad Whitford credited to Ron Pownall Boston

The coils of the L-90 were approximately one quarter inch apart, unlike typical humbucking pickups and the latter L-500, and more like two single coils in one package.

The "holy grail" of "Bill Lawrence" electric guitar pickups, the L-90 is still highly sought after and considered by many to be superior to the L-500. One reason for this may be the L-90s superior ability articulating chords/strumming. The up and down strokes on a L-500 equipped instrument is known to produce a slightly different sounds, whereas the L-90s tone is consistent.

There have been some enquiries as to the differance between white/cream and black L-90s. It seems that quite commonly a white L-90 will appear in the bridge postition with a black on in the neck position. I can only guess at this time that the white ones are L-90XL and black ones art standard L-90 or L-90R (if such a thing excisted). Let me know if you have more info on this.

The L-90XL was replaced by the L-500 in 1979.