IEEE Light-emitting diode (LED) based visible light communication (VLC) has recently been promoted by lighting industry for providing services and information for consumers in shopping malls. Communication system designs require well defined signal-to-noise ratio (SNR). Being semiconductor devices, both of LEDs and photo-detectors are highly temperature-sensitive. This research explores the electrical and thermal sensitivities of LED and photo-detector together for VLC applications, and highlights the discoveries that the SNR of LED based VLC could vary substantially over the full operating power range of the LED lighting systems. A new analysis of the SNR based on the photo-electro-thermal theory has been developed. It can be used as the theoretical and design tool to predict such SNR variations. The validity of the new analysis has been confirmed with practical measurements that are consistent with theoretical predictions. The analytic approach can in principle be used as a design tool for LED based VLC.