hi,

im doing my first project and i have some questions.

i buy the some leds that i find here in mexico, with this specifications:
1.3 V, 20mW, 940 (nm), 12°, 5mm.

i want to know if this leds works fine ??

i have an acrylic with 90 cm x 60 cm

my next question is, which is the best distance between leds.

and just the last question for a FTIR which sizes needs to have IR leds, just 2 sizes?? or the 4 sizes of the acrylic.

thanks and hope you can help me.

12° is not optimal for FTIR. better would be at least twice as big angle.
with 12° LEDs you will have to put them at an angle towards the acrlic itself to make it work.
look here why: http://tools.nuigroup.com/FTIR/

look at the mW/sr data of the LEDS. this shows the real brightness. this value
should be high. there are a lot LEDs to buy which dont suit MT because they are too dim.

940 nm is also not the best choice. most cameras are more sensitive to
lower wavelenghts (near the visible spectrum) like 850 or 880.

distance of 1” apart is pretty commmon.

thanks for your recommendations i will check it.