I noticed a strange phenomenia last summer while I was working on an infrared encoding/decoding project.
I had just programmed the both devices and powered up their breadboards while I searched for a clear-lens infrared LED. Since I also had visible clear-lens LEDs at the time, so I wound up inserting many of those first as I tried to ferret out the infrareds.
During the process I noticed the decoder was receiving RC5 codes from all of the visible LEDs, despite having used an IR detection module. While this only worked for much shorter ranges (around 6 feet versus the 30ft. I normally get indoors), the RC5 bit checking confirmed the data each time. The LEDs were red, white, and blue with the data modulating a 38kHz carrier.
How was the module able to recieve these signals? Is it possible the module's optical filter is wide enough to receive red and blue light? Or were these IR wavelengths coming from the LEDs? Also, I've noticed visible LEDs often appear white when viewed by my CMOS camara--which is an indicator of IR activity. Is it practical to use this IR for short range signaling?