An alternative method utilizes photometry to measure the intensity of light passing through different filters. Each filter allows only a specific part of the spectrum of light to pass through while rejecting all others. A widely used photometric system is called the Johnson UBV system. It employs three bandpass filters: U ("Ultra-violet"), B ("Blue"), and V ("Visible"); each occupying different regions of the electromagnetic spectrum.
Un mètode alternatiu usa la fotometria per a mesurar la intensitat de la llum en passar per diferents filtres. Cada filtre sols permet passar una part específica de l' espectre de la llum, mentre que refusa tots els altres. Un sistema fotomètric molt usat és l' anomenat Johnson UBV system (sistema UBV Johnson). Empra tres filtres de pas de banda: Les regions U ("ultraviolat"), B ("blau") i V ("visible"); cadascun ocupa diferents regions de l' espectre electromagnètic.