 On the other hand, if the emission polarizer is horizontally polarized, two decay times will again be recovered the first one with a positive pre-exponential factor and will be equivalent to formula_7 but the second one will have a negative pre-exponential factor resulting from the introduction of excited molecules that were initially vertically polarized and became depolarized via Brownian motion.The fluorescence sum and difference can be constructed by addition of the decays and subtraction of the fluorescence decays respectively