Emission Specturm: Lightning-Link Antibody Labeling Kit [Allophycocyanin/Cy5.5] [764-0015] - APC/Cy5.5 is a tandem conjugate. The APC is excited at 633nm and functions as an energy donor for the Cy5.5. Energy is transferred from the APC to the Cy5.5 via FRET (Fluorescence Resonance Energy Transfer). The Cy5.5 emits then the energy received from the APC in the form of long wavelength light at 694nm.