How can I compare the output of IR LEDs, specified in watts, to visible LEDs, specified in millicandelas?
Q. It seems that the optical output IR LED’s is generally given in milliwatts and phototransistor/diode sensitivity is given in flux density, lux or millicandelas. The only connection that I can find between the two is that 1 W = 683 lm at 555nm. A. First of all, you only need the efficacy of Si photodetectors to predict photocurrent from incident power. Of course, it varies as a function of wavelength, but at 880nm, it is about 0.5 Amps/Watt. Simply multiply the incident power produced by the IR LED by this value to get photocurrent. At other wavelengths, use the appropriate values from the efficacy curves published in datasheets. However, you won’t see much variation from photodiode to photodiode. Silicon detectors all have pretty much the same curve, reaching a peak around 900nm and falling off roughly linearly toward the shorter wavelengths, crashing precipitously beyond 950nm or so. It can be difficult to calculate incident power from datasheet values, particularly for visible emi
Related Questions
- Visible LEDs seem to be specified in millicandelas, while IR LEDs are specified in milliwatts. What are millicandelas (mcd) and how can I compare them to milliwatts?
- How can I compare the output of IR LEDs, specified in watts, to visible LEDs, specified in millicandelas?
- How does the power consumption of LEDs compare with other systems?
