Absorbance microplate reader - Buying a filter (Feb/04/2011 )

Hi
I am working on a lab and we have an Absorbance Microplate reader Elx-800 (Biotek) and it has 4 filters: 340nm, 405, 490 and 630 nm; it has still a space for one more filter, so, as from 490 to 630 there is a big range, I have 2 main options: 550 and 562 nm. I don't know which one could I buy, or if maybe another wavelength would be suitable, based on the most used filter in lab techniques.
Thanks for the help.

If you don't know wich filter you need, don't buy it because you don't need it. Save your money until you know wich filter you need.