Disclosed is an assembly of light-emitting units, which is applicable to a lighting device that comprises a plurality of light-emitting elements respectively mounted to heat dissipation units. The light-emitting elements give off light beams that project outward through a light-transmitting hood. One surface of the light-transmitting hood is provided with a light diffusion layer featuring light refraction. As such, the light beams emitting from the light-emitting elements are made converging on a light incidence area, which, together with the feature of light spreading of the light-transmitting hood, can spread off and thus homogenize the light beams to form a surface source, and can also concentrate the light energy of the lighting device to enhance the brightness. The lighting device can be applied to any lighting facility.