| F | SK | MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING |
| F21 | USK | LIGHTING; HEATING |
| F21 | KL | LIGHTING (electric aspects or elements, see section H, e.g. electric light sources H01J , H01K , H05B) |
| F21H | UKL | INCANDESCENT MANTLES; OTHER INCANDESCENT BODIES HEATED BY COMBUSTION (arrangements thereof F21V 36/00; burners F23D) |
| F21K | UKL | LIGHT SOURCES NOT OTHERWISE PROVIDED FOR |
| F21L | UKL | LIGHTING DEVICES OR SYSTEMS THEREOF, BEING PORTABLE OR SPECIALLY ADAPTED FOR TRANSPORTATION [1, 7] |
| F21M | GEL | (transferred to F21S; F21V) |
| F21P | GEL | (transferred to F21S; F21V) |
| F21Q | GEL | (transferred to F21S) |
| F21S | UKL | NON-PORTABLE LIGHTING DEVICES OR SYSTEMS THEREOF [1, 7] |
| F21V | UKL | FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR [1, 7] |
| F21W | UKL | INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21L , F21S and F21V , RELATING TO USES OR APPLICATIONS OF LIGHTING DEVICES OR SYSTEMS [7] |
| F21Y | UKL | INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21L , F21S and F21V , RELATING TO THE FORM OF THE LIGHT SOURCES [7] |