More info needed:

Sourve Voltage: 9v
LED Forward Voltage:
Resistor:
Battery brand & type: (NIMH/NICAD/etc)

benpaddlejones

hi,


certainly not true.
standard leds usually want 10-20mA current for a good visibility.
low current leds reduce this requirement to 1-2mA. their visibility is still good, but they (obviously) arent as strong as standards regarding their emission (check the datasheets, they should state the emission intensity in mW, sometimes at different current levels).

for ir leds to work as intended, this emission usually needs to be quite high (the higher the better), therefor most ir leds are built for MUCH higher currents... typical leds are specified for 20-50mA, most of them even work up to 100-150mA limits. some special high performance ir leds for very long range uses even work with 500mA+.
generally, ir leds driven with less current than you would drive standard leds with (<20mA) most likely wont give you good results.

if you want to make the most out of your battery lifetime and still get as good results as possible you should
1. use the wavelength the sensor is most sensitive to (apparently 940nm for the wii camera, 950nm - which is quite a standard - should work, too and give much better results over other ir leds in the 850's range).
2. use leds with the best mW/mA ratio you can find.

Be careful to look at mW (total radiated power) rating, and not mW/sr.  The later is a measurement of angular energy density, and can vary dramatically based on measurement technique and viewing angle of the LED.  Unfortunately few datasheets actually publish mW ratings, only mw/sr.

Another useful metric is quantum efficiency.  electrical power * quantum efficiency > optical power.  For example, a 100mA 1.3V 70% efficient LED would have a total radiant a bit below 91mW (less due to optical properties of the package).  It's rare however to find a datasheet that lists QE but not TRP.