Photolytic damage is expected to be mainly a function of "dosage", i.e., the amount of radiation remaining in the specimen as sunlight or similar radiation is incident on the specimen. Photolytic damage is expected to be wavelength specific, partly because different wavelengths contain different amounts of energy per photon and partly because the chromophore changes as the wavelength of the incident radiation is varied over tens of nanometers. Photolytic damage is to a first approximation independent of time.

     Hydrolysis is attainment of an equilibrium specified by the concentrations of hydrolysable groups and water in the material (typically expressed in moles/Liter) and of the temperature of exposure. Because hydrolysis is a relatively slow process, it, unlike photolytic damage, is a function of time.

     In the experiments carried out to date, damage has been monitored quantitatively by changes in IR spectra. This is certainly adequate for the purposes, but other quantitative evidence of damage could be used.

     The dosage was estimated from UV spectra of the lamps and the filters (used to isolate a particular wavelength range), and from the UV absorption of the specimens themselves. These quantities were observed to change with time. For example, the lamps aged. The experimental procedure is therefore to monitor the changes (using the appropriate UV spectra) over short ranges of time over which any change is presumed to be linear. Once the output of the lamp and the transmission of the filter are known, the amount of radiation incident on a specimen can be estimated. From the specimen absorbance, the transmission of the specimen is known. Radiation incident on the specimen but which does not emerge at the other side of the specimen is presumed to have been absorbed by the specimen and is taken as being the apparent dosage. Whether to consider that all the absorbed radiation leads to degradation or whether some radiation is considered to be "harmlessly" absorbed by degradation products rather than by the original coating material is a choice offered by the programs.

     A model must successfully account for effects seen in the experiments before it can be used to generate prophesies. But before a model can be proposed, the effects must be visible, i.e., above the noise. The noise levels in the measurements are very important, first in determining whether or not the effects of the experiments are discernible and second in determining the applicable range (in time or radiation level or hydrolysis level) of any prophesy.