Candela (cd)

The candela is the SI unit of luminous intensity — luminous flux emitted per unit solid angle in a specific direction. Where lumens describe total output, candela describes how strongly light is concentrated in a direction: a narrow-beam floodlight and a wide diffuse fixture can emit identical lumens with radically different peak candela. Luminaire photometric files (IES/LDT) are essentially tables of candela values across angles, which is what lighting-design software uses to predict illuminance point by point. Peak candela matters for aiming sports floodlights and for glare assessment, where high intensity toward the eye drives discomfort.