Figure 2.

FRET efficiency distribution constructed from the fluorescence bursts containing >30 photons in free diffusion experiments. Due to fluorescence quenching in the folded state, bursts from the folded state are rarely observed. (Purple-dashed curves) Expected distributions arising from shot noise for n_A + n_D = 30 photons ($\sigma =\sqrt{E(1-E)/(n_{\mathrm{A}}+n_{\mathrm{D}})}$). Shot noise only accounts for 50% of the variance of the distribution. (Orange lines) Center of the distribution from a single Gaussian fit.