Photometry with a unique form of spectrophotometer devised by the Dutch astronomer Theodore Walraven (1916–2008) and his wife Johanna Helena Walraven, née Terlinden (1920–89). There are no filters; instead, the wavelength ranges are defined by quartz lenses and prisms. The names of the wavebands with their wavelengths and bandwidths are W, 325 and 14 nm; U, 363 and 24 nm; L, 384 and 23 nm; B, 432 and 45 nm; and V, 547 and 72 nm. All five bands are observed simultaneously.