Wiimote Project

I'm wondering if anyone knows more information about LEDs.  I have two questions.
First, I noticed that the TSAL6400 has a radiant intensity of 40 mW/Sr.  I'm assuming that this is an indication of how bright the light is.  The TSAL6100 has a smaller dispersion angle than the 6400 (10^o instead of 25^o) but has a radiant intensity of 130 mW/Sr.  This should make it a lot brighter, right?  I've also read that a lot of the IR light that the wiimote picks up is reflected off the white board surface ... so again, the brighter the better, right?  All other specifications between the two seem the same.   
Secondly, if a battery starts to become underpowered because the voltage falls too low, does the LED cease to work altogether, or does it just get dimmer and dimmer like an incandescent light bulb does?  If it does get dimmer, would the 6100 with a higher radiant intensity last longer on a lower voltage than the 6400?  In other words, say the voltage hits 1.1 V (or whatever voltage is too low) and the IR signal from the 6400 is now too low to be registered by the wiimote.  Would the 6100 still be bright enough at 1.1 V because it has a higher "native" radiant intensity?  I would really love to get the most out of my 1.2 V NiMH rechargeable battery.

I'm wondering if anyone knows more information about LEDs.  I have two questions.
First, I noticed that the TSAL6400 has a radiant intensity of 40 mW/Sr.  I'm assuming that this is an indication of how bright the light is.  The TSAL6100 has a smaller dispersion angle than the 6400 (10^o instead of 25^o) but has a radiant intensity of 130 mW/Sr.  This should make it a lot brighter, right?  I've also read that a lot of the IR light that the wiimote picks up is reflected off the white board surface ... so again, the brighter the better, right?  All other specifications between the two seem the same.   
Secondly, if a battery starts to become underpowered because the voltage falls too low, does the LED cease to work altogether, or does it just get dimmer and dimmer like an incandescent light bulb does?  If it does get dimmer, would the 6100 with a higher radiant intensity last longer on a lower voltage than the 6400?  In other words, say the voltage hits 1.1 V (or whatever voltage is too low) and the IR signal from the 6400 is now too low to be registered by the wiimote.  Would the 6100 still be bright enough at 1.1 V because it has a higher "native" radiant intensity?  I would really love to get the most out of my 1.2 V NiMH rechargeable battery.

Hi Skimmer,

The radiant intensity is the power intensity that is transmitted radially from the LED. From the details you provided, it seems that the TSAL6100 has a focused transmission  compared to the TSAL6400. Depending on the purpose of the IR LED, this may be used instead of the TSAL6400. If you are looking to have a bigger blob, the TSAL6400 will be better. For example, at a large distance away from the Wiimote, the IR blob may be too small for the Wiimote.

The LED is a diode, thus there is a minimum forward voltage that will put the diode in forward mode to allow current flowing through. If the minimum forward voltage is not reached, the diode will prevent current from flowing through unlike a incandescent light bulb does. The light bulb will get dimmer and operates at a non-efficient/optimum level if the correct voltage is not used. For the LED, at the borderline forward voltage level (around the voltages as specified in the technical specifications of the LED), we usually see it get dimmer also. This would be best to be experimented with to ensure that it is working well with the Wiimote.

Regards,
Boon Jin