The most commonly used red (i.e. 600–1100 nm) photometric system with two filters, called R and I, of effective wavelengths and bandwidths 641 and 158 nm, and 798 and 154 nm, respectively. R − I is more sensitive to temperature than B − V for cool stars because of the number of lines and molecular bands in the B and V passbands. It was originated by the American astronomer Gerald Edward Kron (1913–2012) and modified by the South African Alan William James Cousins (1903–2001).