Half-Lambert
A shading trick that bends Lambert's diffuse model so surfaces never go fully black on the shadowed side.
Lambert's law takes diffuse brightness from the dot product of surface normal and light direction; anything past 90° clamps to zero and thus pitch black. Half-Lambert remaps that dot product into the 0–1 range (×0.5 + 0.5) and often squares the result, so light wraps around the object and the far side keeps a faint glow.
Valve introduced the trick in Half-Life (1998) to stop low-poly characters looking flat and harsh. It is physically wrong — energy appears from nowhere — but cheap and flattering, especially for skin and soft materials, and it survives as a stylised alternative to Phong and Blinn-Phong.