  Throughout the year 2011, the Large Hadron Collider (LHC) has operated with
an instantaneous luminosity that has risen continually to around 4x10^33cm-2
s-1. With this prodigious high-energy proton collisions rate, efficient
triggering on electrons and photons has become a major challenge for the LHC
experiments. The Compact Muon Solenoid (CMS) experiment implements a
sophisticated two-level online selection system that achieves a rejection
factor of nearly 106. The first level (L1) is based on coarse information
coming from the calorimeters and the muon detectors while the High-Level
Trigger (HLT) combines fine-grain information from all sub-detectors. In this
intense hadronic environment, the L1 electron/photon trigger provides a
powerful tool to select interesting events. It is based upon information from
the Electromagnetic Calorimeter (ECAL), a high-resolution detector comprising
75848 lead tungstate (PbWO4) crystals in a "barrel" and two "endcaps". The
performance as well as the optimization of the electron/photon trigger are
presented
