John Guild (1889–1979) was a British physicist specialized in optics, later transferred his focus on other studies.

Guild worked at the National Physical Laboratory (NPL) at Teddington in England.

He was essential to the creation of the Colour Group in the United Kingdom.

He is best known for collecting the data based on empirical evidence on the light sensitivity of the receptors and cones of the human eye.

[1] This work and the experiment of William David Wright is the foundation of the international standardization of color measurement, the CIE 1931 Standard Colorimetric Observer.