The magnitude of a star as measured through the infrared L filter of the Johnson photometry system. The L filter has an effective wavelength of 3450 nm and a bandwidth of 472 nm. More recent observers have redefined the L filter to avoid the worst of the absorption bands in the Earth’s atmosphere. The new filter has a longer central wavelength of 3830 nm, bandwidth 510 nm, and is called L′. There is also an L magnitude in Walraven photometry, but the context should make clear whichever is intended.