Fig. 1: Fluorescence reporting for retrieving light intensity.

a, First protocol with a fluorescent actinometer. A jump of constant light I is applied onto the actinometer. The time evolution of its fluorescence signal F is recorded and fit with a monoexponential curve to extract its characteristic time τ. I is retrieved from τ by using the photoconversion cross section σ of the actinometer. b, Five fluorescent actinometers covering the UV-vis range in action. Monoexponential fit of the time evolution of the normalized fluorescence signal F(t)/F(0) provides τ (Supplementary Table 3). c, Second protocol with a fluorophore to transfer information on light intensity from one wavelength to another. Lights at wavelengths λ₁ (with intensity I₁, known) and λ₂ (with intensity I₂, to be measured) are successively applied onto the fluorophore and the associated fluorescence signals F₁ and F₂ are recorded at a same emission wavelength. I₂ is extracted from F₁ and F₂ by using I₁ and the tabulated fluorescence excitation spectrum ϵ(λ) of the fluorophore. d, Absorption (ε(λ); dotted line) and normalized fluorescence excitation (ϵ(λ); solid line) spectra of DDAO. ε(λ₁) and ε(λ₂) indicated by blue and green disks, respectively, are used to retrieve I(λ₂) in c (text and Supplementary Tables 1–3).