Most turbidity meters perform a nephelometric measurement, which means that the meter measures the amount of light scattered at a 90 angle. The light source of this nephelometric measurement is different between the ISO and the EPA compliant turbidity meter. To be ISO compliant (ISO standard 7027) the meter must be equipped with a light emitting diode (LED) with a wavelength of 860 nm and a spectral bandwidth of less than or equal to 60 nm. ISO standard 7027 is an international standard that is used frequently in Europe. The EPA method, on the other hand, requires a tungsten lamp, with a color temperature of 2,200 3,000 K, for the turbidity meter to be EPA compliant (EPA method 180.1). EPA method 180.1 is the regulated standard used for most drinking water applications in the USA and Canada.