Sonic Transmitter Module RT-EL/PX for L-858D-U Speed master light meter. Used to trigger Lunchroom(Sky port) and Phot tix (Strata) enabled lighting and receivers. When used with Lunchroom provides Triggering and controlling the power level of the light •Triggering and controlling the power level of modeling lamp with ON/OFF •For more information on Lunchroom, When used with Phot tix Selecting the groups and triggering a flash for measurement requires using a Phot tix Indre, Metros+ set for Stratum II reception or flash attached to Phot tix receiver with Stratum II protocol. •For more information about Phot tix and the Stratum II protocol, see the website of Phot tix