Traditionally optical multichannel analyzers (OMAs) have been turnkey instruments. Controllers are now available which replace the OMA console with the users existing computer. The increased flexibility of this approach comes at the expense of increased involvement in the details of system operation. This is particularly the case for pulsed experiments where the detector is gated on for short periods. We report here implementation of an OMA controller hosted by an IBM personal computer using IEEE‐488 communication. A microchannel‐plate intensified detector is used in gated mode to collect spectra of intermediates formed by nanosecond laser photolysis. Three different pulsers for intensifier gating are compared. Both conventional absorbance measurements on transparent samples and diffuse reflectance measurements on opaque low‐temperature matrices are described. In both cases, however, the samples are sufficiently photostable that noise can be reduced by signal averaging using repeated photolysis of the same sample volume. A second paper describes the additional complexity required for high signal‐to‐noise measurements on small quantities of photolabile samples.