If different leaf absorption ratios are an issue, or they are an unwanted variable, then using Y ( II ) instead of ETR, may be the best choice.
12.
His principle, however, has endured : it was that for heat rays of the same wavelength, in equilibrium at a given temperature, the wavelength-specific ratio of emitting power to absorption ratio has one and the same common value for all bodies that emit and absorb at that wavelength.
