Abstract: A modular construction system light matrix comprising a housing having side walls, an end wall and a front edge encircling a front opening of said housing. The light matrix has an array of light emitting elements. The light matrix has a compartment grid, arranged in said housing and having compartment grid walls extending towards said front opening of the housing, one compartment for each light emitting element. The light matrix has a light diffusing element arranged at said opening of the housing having a plurality of diffuser tiles, each diffuser tile covering a compartment of the compartment grid. The diffusing element comprises a diffuser grid providing a barrier between mutually facing sidewalls of the diffuser tiles. The diffuser grid is formed in a different material from the diffuser tiles. A lower side of the diffuser grid adapted to abut an upper side of the compartment grid.