This four-filter BrightLine fluorescence set is specially designed to achieve high-performance fast ratiometric imaging of Ca2+ using Fura-2 as an indicator. The carefully optimized excitation filters provide superb balance of free and saturated Ca2+ signals, while minimizing the crosstalk and noise, resulting in the most accurate ratiometric measurements. The high signal throughput of the filter set permits reliable Fura-2 (Ca2+) measurements, even when using light sources of relatively limited ultraviolet output. Independent laboratories have measured this set to have 2-4X the free and saturated signals as compared with filters from the leading competitor.