A Pair of Light Emitting Diodes for Absorbance Measurement

an emitter and a photodiode. 14 In this report, a pair of LEDs was used to make absorbance measurement. The first LED was a light source as a solid-state light source (i.e. emitter LED) and the other was used as a photodiode (i.e. detector LED). When light illuminates the emitting chip of an LED, small amount of current (~nA level) can be produced. We were using an operational amplifier to amplify photocurrents registered on the detector LED directly. Compared to other light transducers like silicone based photodiodes, a LED is known to be more sensitive to the same wavelength which the LED emits. Bromothymol blue (BTB) was used as a test dye. The red LED’s emission spectra and relative sensitivity in terms of wavelength was also reported here. The test dye’s absorption spectra, linear range of the calibration curve, and limit of detection were also measured. Experimental