A flat light source including a first substrate, a second substrate, a sealant, several sets of dielectric pattern and a phosphor layer is provided. The first substrate has electrodes thereon. The sealant is disposed between the first and second substrates to form a space between the first and second substrates and the sealant. These sets of dielectric pattern are formed in the space between the first and second substrates. Each set of dielectric pattern has at least two dielectric strips, and each dielectric strip covers one of the electrodes correspondingly. Each dielectric strip has a top surface and two side surfaces, and the top surface has an uneven contour. The phosphor layer is disposed between the two dielectric strips of each set of dielectric pattern, and the phosphor layer is further disposed on the top surface of the dielectric strips.