Filter choice

Reading the OSRAM SFH485 datasheet again today - it seems a good idea not to buy a filter until I have the complete wiring of the Urail frames.

The LEDs are 880nm, but this is exactly at 100mA, there is +- 40nm variance depending on the current, chances are I am not going to have the exact 100mA. Based on most LED online calculators (see links on the right) I will get ca. 90mA with my 19V supply. So if I buy the 880nm pass filter from e.g. ebay and my LEDs shine @ 840nm I will not get a single blob.

SO, waiting for the 100 LEDs, install them on the frame,connect everything and measure amperage and then go for the proper filter, maybe one that is 800 to 900nm.

Anyone tried to measure wavelength? how exactly do I do that?

cheers,
P