| F | SK | MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING |
| F21 | USK | LIGHTING; HEATING |
| F21 | KL | LIGHTING |
| F21H | UKL | INCANDESCENT MANTLES; OTHER INCANDESCENT BODIES HEATED BY COMBUSTION |
| F21K | UKL | LIGHT SOURCES NOT OTHERWISE PROVIDED FOR |
| F21L | UKL | LIGHTING DEVICES OR SYSTEMS THEREOF, BEING PORTABLE OR SPECIALLY ADAPTED FOR TRANSPORTATION [1, 7] |
| F21S | UKL | NON-PORTABLE LIGHTING DEVICES; 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 F21K, F21L, F21S and F21V, RELATING TO USES OR APPLICATIONS OF LIGHTING DEVICES OR SYSTEMS [7] |
| F21Y | UKL | INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED [7] |