<P> A complete spectrum of the absorption at all wavelengths of interest can often be produced directly by a more sophisticated spectrophotometer . In simpler instruments the absorption is determined one wavelength at a time and then compiled into a spectrum by the operator . By removing the concentration dependence, the extinction coefficient (ε) can be determined as a function of wavelength . </P> <P> UV - visible spectroscopy of microscopic samples is done by integrating an optical microscope with UV - visible optics, white light sources, a monochromator, and a sensitive detector such as a charge - coupled device (CCD) or photomultiplier tube (PMT). As only a single optical path is available, these are single beam instruments . Modern instruments are capable of measuring UV - visible spectra in both reflectance and transmission of micron - scale sampling areas . The advantages of using such instruments is that they are able to measure microscopic samples but are also able to measure the spectra of larger samples with high spatial resolution . As such, they are used in the forensic laboratory to analyze the dyes and pigments in individual textile fibers, microscopic paint chips and the color of glass fragments . They are also used in materials science and biological research and for determining the energy content of coal and petroleum source rock by measuring the vitrinite reflectance . Microspectrophotometers are used in the semiconductor and micro-optics industries for monitoring the thickness of thin films after they have been deposited . In the semiconductor industry, they are used because the critical dimensions of circuitry is microscopic . A typical test of a semiconductor wafer would entail the acquisition of spectra from many points on a patterned or unpatterned wafer . The thickness of the deposited films may be calculated from the interference pattern of the spectra . In addition, ultraviolet - visible spectrophotometry can be used to determine the thickness, along with the refractive index and extinction coefficient of thin films as described in Refractive index and extinction coefficient of thin film materials . A map of the film thickness across the entire wafer can then be generated and used for quality control purposes . </P> <P> UV / Vis can be applied to determine the kinetics or rate constant of a chemical reaction . The reaction, occurring in solution, must present color or brightness shifts from reactants to products in order to use UV / Vis for this application . For example, the molecule mercury dithizonate is a yellow - orange color in diluted solution (1 * 10 ^ - 5 M), and turns blue when subjected with particular wavelengths of visible light (and UV) via a conformational change, but this reaction is reversible back into the yellow "ground state". </P> <P> The rate constant of a particular reaction can be determined by measuring the UV / Vis absorbance spectrum at specific time intervals . Using mercury dithizonate again as an example, one can shine light on the sample to turn the solution blue, then run a UV / Vis test every 10 seconds (variable) to see the levels of absorbed and reflected wavelengths change over time in accordance with the solution turning back to yellow from the excited blue energy state . From these measurements, the concentration of the two species can be calculated . The mercury dithizonate reaction from one conformation to another is first order and would have the integral first order rate law: ln (A) (time t) = − kt + ln (A) (initial). Therefore, graphing the natural log (ln) of the concentration (A) versus time will graph a line with slope - k, or negative the rate constant . Different rate orders have different integrated rate laws depending on the mechanism of the reaction . </P>

If a solution is blue what color will it show the most response in terms of absorption