Molecular photochemistry is an integral field in chemistry. Despite this, it is often difficult to demonstrate an effective hands-on experiment that offers a unique opportunity to students to observe photochemistry in action. Although simple laboratory experiments which use a UV-vis wavelength lamp do provide some photochemical information, the student does not have a first-hand visual account of the evolving excited state process. In this paper, we present a simple and cost-efficient laboratory apparatus that may be used in the undergraduate research and teaching laboratories to study the "in situ" photochemistry of several classes of chromophores. The technique is based on pump-probe transient absorption spectroscopy. A solution containing the organic molecules of choice is placed in a portable commercial UV-vis absorption spectrometer: oxybenzone (2-hydroxy-4-methoxybenzophenone) and phenol in hexane were chosen to test the setup. The sample is then continuously irradiated via a judiciously positioned high-power UV-vis light-emitting diode to initiate the electronic excitation. The sample absorption spectrum is manually recorded at various time delays. Photokinetic data is then obtained in order to quantify the excited state reaction. We also show how accompanying electronic structure calculations may be used to determine the various photoproducts formed during the photoreaction. This joint experimental and theoretical endeavor gives students a unique opportunity to observe the evolving chemistry of a light-induced reaction and allows them to gain experience in computational chemistry when characterizing their data using contemporary electronic structure methods.