Multi-color Reference Standards are highly uniform microspheres which fluoresce over a broad range of the spectrum to provide several reference positions in multi-detector analysis. This standard is used to properly align your flow cytometer excited from UV to near IR; this standard emits over the entire spectrum.
A test requires one drop (50μl) of particle suspension, which is equivalent to ~100,000 particles. Bangs Flow Cytometry Standards are 7-9μm in diameter to approximate the size of human lymphocytes.