Ratio imaging of intracellular calcium has long been an important technique in cell biology, neuroscience and related fields. Excitation ratio imaging compensates for variations of indicator dye concentration within cells and between cells that might otherwise be interpreted as calcium level changes. The preferred indicator dyes for Ca2+ ratio imaging are typically fura-2 and the recently developed red-shifted analog fura-8. Excitation ratio imaging is conventionally implemented using a white light source in combination with mechanically alternated filters to select the desired excitation wavelengths (340 and 380 nm for fura-2, 360 and 400 nm for fura-8). Lumencor’s AURA Light Engine generates these excitation outputs from two discrete electronically controlled solid-state light sources. The AURA Light Engine can accommodate up to five sources, providing additional outputs for optogenetics or GFP/mCherry excitation. Our RETRA Light Engine can be configured with 360/28 nm and 395/25 nm outputs for customers requiring a dedicated two-channel excitation source. Electronic alternation of excitation wavelengths provided by AURA or RETRA Light Engines is faster and more reproducible than mechanical methods. In turn, this allows higher-speed data acquisition, providing increased temporal resolution for recording elementary processes in cell physiology.