Hi all, this might be a naive question but why do the different LED openings have different shape holes? On the inside of the sleeve i mean. Is there a reason why they are not all round?
That’s a good question @Eleni_M. We originally did have them all as the same round holes, but realized that we can improve the optics by customizing them. For example, the X1 and X2 positions are designed for maximum exposure (since they are used for external LEDs). The IR LED position is a tighter hole, since we want nearly collimated light. The PDs have a half-moon like shape so that light that might scatter off the stir bar is less likely to hit the PD. etc. etc.
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I see. I get the reason for the half-moon now, which was the one that confused me to begin with.
But what do you mean by external LEDs?
External LEDs might be additional white light LEDs used in photosynthetic cultures.
Ah ok i get it now…thanks for the explanations 
if i may reopen this topic, can the angle between the IR led and PDs be altered without affecting the reading?
for instance, would 30 deg be ok?
