A spectrum splitter is an optical device designed to separate light or other forms of electromagnetic energy into its component wavelengths. This process is fundamentally different from a simple power divider, which merely reduces signal strength across multiple outputs. Combining two or more solar cells with different bandgaps into a multi-junction tandem solar cell lowers thermalization losses and increases the power conversion efficiency. Infrared radiation interacts with molecules by changing their. Spectral splitters, as well as solar concentrators, are commonly designed and optimized using numerical methods.