The use of light-emitting diodes (LEDs) as photonic reporters of electrochemical reactions is examined and compared to an electron-to-photon conversion strategy involving electrogenerated chemiluminescence (ECL). The results indicate that it is possible to evaluate the rate of electrochemical reactions photonically without making direct current measurements. Compared to ECL, LED reporting has the following performance benefits: lower threshold current for photon emission, more efficient and stable electron-to-photon conversion, and larger dynamic range. Electrochemical reactions occurring in an array of ten thin-layer electrochemical cells are simultaneously evaluated using a corresponding array of LEDs. (c) 2005 The Electrochemical Society. All rights reserved.