# What is the wavelength of an Itron C1S IR LED?

I'm trying to find an appropriate IR Phototransistor for an Itron Centron C1S Meter. But I can't figure out exactly what is the wavelength of the IR transistor used by Itron.

Do meters have standard IR LEDs? Does it really matter, or can I just get any IR Phototransistor like the TCRT5000 (only the IR Phototransistor)?

• I doubt they use a specific wavelength, just a "handshake" of some sort, to key in the device. Otherwise universal remote manufacturers would have a hell of a time. – Daniel B. May 29 '14 at 4:12

Measure the voltage drop across the junction. The band gap energy of the diode junction is also the energy of the photons in electron Volts (eV). Find the wavelength with $$\lambda =\frac{hc}{\mbox{E}}=\left( 4.1366\times 10_{eVs}^{-15\; } \right)\times \; \frac{\left( 3\times 10_{\frac{m}{s}}^{8} \right)}{measu\mbox{re}d\; voltage}$$ Multiply by by 1,000,000,000 or use 3x10^17 for nanometers. You can do this with red or green LEDs and a spectroscope to verify.