My PhD programme of research with the Adaptive Information Cluster at the National Centre for Sensor Research has focussed on the development of low cost, low powered optical sensing devices. Part of this work was carried out in collaboration with Mitsubishi Electric Research Labs, Boston, USA and was funded by Science Foundation Ireland (SFI). The optical sensing devices were developed as alternative analytical tools for colorimetric based sensing. The main aim of this work was to design and develop these LED based devices, but some applications were also explored, including the use of the devices for the determination of the pH of a solution and the detection of Fe (II). Transmittance and reflectance based devices were developed and both configurations generated sensitive and reliable data. The circuitry used to operate the devices was simple (no A/D converter required) and inherently digital. All of the devices were operated using a 9 V battery. Overall it can be concluded that all of the LED based optical devices are inexpensive, portable and easy to operate.