Candela (cd) is the SI unit of luminous intensity. It describes the amount of visible light emitted in a particular direction per unit solid angle. Candela is useful for comparing the reach and directional intensity of different light patterns. Unlike lumens, which describe total luminous flux, candela is directional. A lamp can have moderate total output but high candela if its optics concentrate the light into a narrow pattern. Candela values are therefore useful for assessing long-range performance, but the full intensity distribution or isolux diagram is needed to understand coverage outside the peak direction.