Table 1. Summary of Variables.

Variable	Description
$t$	Time of photon emission (in s)
$r$	Distance between the donor and acceptor (in Å)
$Decay\left(t\right)$	Time-dependent decay of the donor fluorescence (in counts)
$DecayB\left(t\right)$	Time-dependent decay of the buffer-only fluorescence (in counts)
$I_{DA}\left(t\right)$	Model estimate of the fluorescence lifetime of the donor in the presence of the acceptor (in counts)
$I_B\left(t\right)$	Model estimate of the fluorescence lifetime of a buffer-only sample (in counts)
$IRF\left(t\right)$	Measured instrument response function (in counts)
${bkgr}_{dec}$	Time-independent decay background (in counts)
${bkgr}_{irf}$	Time-independent background of the instrument response function (in counts)
${shift}_{irf}$	Time shift between the instrument response function and the measured decay (in ps)
$f_B$	Scaling of the buffer fluorescence
$A_0$	Amplitude of the model estimate of the fluorescence lifetime of the donor (in counts)
$f_D$	Fraction of donor-only fluorescence in the sample
${\alpha }_{Di}$	Fraction of the ith component of the donor-only fluorescence (in counts)
${\tau }_{Di}$	Time constant of the ith component of the donor-only fluorescence (in s)
${\alpha }_{Bi}$	Amplitude of the ith component of the buffer fluorescence (in counts)
${\tau }_{Bi}$	Time constant of the ith component of the buffer fluorescence (in s)
$R_0$	Characteristic distance between donor and acceptor producing 50% FRET efficiency
$\rho \left(r\right)$	Probability distance distribution of the donor and acceptor distances
$f_{Ai}$	Fraction of the ith component of the probability distance distribution
${\overline{r}}_i$	Average distance of the ith component of the donor-only fluorescence (in Å)
${\sigma }_i$	Standard deviation of the ith component of the donor-only fluorescence (in Å)