An assembly block (20) including an LED element (51), a control unit (52) that controls the LED element (51), and a housing (30) that holds the LED element (51) and the control unit (52) is provided. The housing (30) includes mechanical interfaces (32, 33) for mechanically connecting to the outside and is at least partially translucent. The control unit (52) includes a first functional unit (111) that stores, on receiving first data sets (D1) that include data for controlling the color of light to be outputted from the LED element (51) and a transfer command via the first electrical interface (79a) associated with the first mechanical interface (32), the first data set (D1) in a buffer (121) and outputs the stored first data set (DS1) in the buffer (121) together with the transfer command via a second electrical interface (79b) associated with the mechanical interface (33) on the second side.