Designed for laboratory use by bioanalytical researchers and/or developers of bio-optical instrumentation. The RETRA incorporates two individually controllable solid state light sources with associated bandpass filters, producing spectrally discrete outputs. Spectral outputs can be situated from the ultraviolet through the visible to the near-infrared, according to application-specific requirements. For example, the RETRA FURA light engine provides 340 nm and 380 nm outputs for fura-2 ratio calcium imaging. The RETRA light engine can be controlled by serial commands for on/off switching and intensity control or by TTL triggering for source selection and on/off switching.