Large enhancement in electroluminescence efficiency and brightness of light-emitting diodes fabricated from binary blends of conjugated polyquinolines was observed compared to devices made from the homopolymers. Blends of poly(2,2'-(2,5-thienylene)-6,6'-bis(4-phenylquinoline)) (PTPQ) and poly(2,2'-(biphenylene)-6,6'-bis(4-phenylquinoline)) (PBPQ), for example, had EL efficiency and luminance of up to a factor of 30 enhancement. Energy transfer was negligible in all four binary blend systems investigated, The electrical proper-ties of the diodes and electric-field-modulated photoluminescence spectroscopy results confirmed that the enhancement of electroluminescence in the blends originated from spatial confinement of excitons which leads to increased exciton stability and electron-hole recombination efficiency. Voltage-tunable and composition-tunable multicolor electroluminescence was observed in the polymer blend devices. The observed composition-dependent new emission bands and enhanced fluorescence lifetimes in the blends were suggested to originate from exciplex formation and molecular miscibility between the blend components. These results demonstrate new phenomena in the electroluminescence and photo-physics of multicomponent conjugated polymers.