are relatively uncommon asteroids
with a strongly reddish spectrum shortwards of 0.75 μm, and a featureless flat spectrum longwards of this. In comparison with the K-type
, they exhibit a more reddish spectrum at visible wavelengths and a flat spectrum in the infrared.
These asteroids were described as "featureless" S-types in the Tholen classification. The L-type was formally introduced in the SMASS classification, although previous studies had noted the unusual spectra of two of its members 387 Aquitania and 980 Anacostia.
A grouping proposed in the SMASS classification for asteroids with an L-like flat spectrum longwards of 0.75 μm, but even redder in visible wavelengths, like the D-type
. An example may be 728 Leonisis
, although it has also been classified as an A-type