A system of intermediate-band photometry in which the names, wavelengths, and bandwidths of the filters are: u, 352 and 31 nm; v, 410 and 17 nm; b, 469 and 18 nm; and y, 548 and 23 nm. Strömgren photometry is often supplemented by two interference filters to measure the strength of the Ηβ‎ line (see hydrogen spectrum). They share the same central wavelength of 486 nm, but have different bandwidths of 15 and 3 nm. The difference in the two magnitudes is the Ηβ‎ index, symbol β‎. The different colours can be combined to determine the temperature, luminosity, and reddening of stars of spectral types O and B. The metallicity can also be determined for stars of spectral types A and F. The system is named after its originator, B. G. D. Strömgren.