# LED openings/holes

**URL:** <https://forum.pioreactor.com/t/led-openings-holes/212>\
**Category:** Hardware, PWM, and Optics\
**Created:** [January 24, 2024, 2:38pm UTC](https://forum.pioreactor.com/t/led-openings-holes/212 "2024-01-24T14:38:43Z")\
**Posts on this page:** 9\
**Page:** 1

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**Author:** ![Eleni\_M](https://forum.pioreactor.com/user_avatar/forum.pioreactor.com/eleni_m/32/129_2.png) [@Eleni\_M](https://forum.pioreactor.com/u/Eleni_M)\
**Post date:** [January 24, 2024, 2:38pm UTC](https://forum.pioreactor.com/t/led-openings-holes/212/1 "2024-01-24T14:38:43Z")

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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?

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**Author:** ![CamDavidsonPilon](https://forum.pioreactor.com/user_avatar/forum.pioreactor.com/camdavidsonpilon/32/3_2.png) [@CamDavidsonPilon](https://forum.pioreactor.com/u/CamDavidsonPilon)\
**Post date:** [January 24, 2024, 3:23pm UTC](https://forum.pioreactor.com/t/led-openings-holes/212/2 "2024-01-24T15:23:01Z")

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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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**Author:** ![Eleni\_M](https://forum.pioreactor.com/user_avatar/forum.pioreactor.com/eleni_m/32/129_2.png) [@Eleni\_M](https://forum.pioreactor.com/u/Eleni_M)\
**Post date:** [January 24, 2024, 4:25pm UTC](https://forum.pioreactor.com/t/led-openings-holes/212/3 "2024-01-24T16:25:47Z")

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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?

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**Author:** ![CamDavidsonPilon](https://forum.pioreactor.com/user_avatar/forum.pioreactor.com/camdavidsonpilon/32/3_2.png) [@CamDavidsonPilon](https://forum.pioreactor.com/u/CamDavidsonPilon)\
**Post date:** [January 24, 2024, 4:55pm UTC](https://forum.pioreactor.com/t/led-openings-holes/212/4 "2024-01-24T16:55:03Z")

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External LEDs might be additional white light LEDs used in photosynthetic cultures.

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**Author:** ![Eleni\_M](https://forum.pioreactor.com/user_avatar/forum.pioreactor.com/eleni_m/32/129_2.png) [@Eleni\_M](https://forum.pioreactor.com/u/Eleni_M)\
**Post date:** [January 25, 2024, 10:16am UTC](https://forum.pioreactor.com/t/led-openings-holes/212/5 "2024-01-25T10:16:20Z")

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Ah ok i get it now…thanks for the explanations 🙂

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**Author:** ![oni6969](https://forum.pioreactor.com/letter_avatar_proxy/v4/letter/o/aca169/32.png) [@oni6969](https://forum.pioreactor.com/u/oni6969)\
**Post date:** [March 3, 2024, 9:54am UTC](https://forum.pioreactor.com/t/led-openings-holes/212/6 "2024-03-03T09:54:17Z")

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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?

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**Author:** ![CamDavidsonPilon](https://forum.pioreactor.com/user_avatar/forum.pioreactor.com/camdavidsonpilon/32/3_2.png) [@CamDavidsonPilon](https://forum.pioreactor.com/u/CamDavidsonPilon)\
**Post date:** [March 3, 2024, 2:43pm UTC](https://forum.pioreactor.com/t/led-openings-holes/212/7 "2024-03-03T14:43:02Z")

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hi @oni6969,

That should be okay. Generally, the closer the angle to 0deg, the lower the sensitivity, but the higher the saturation limit. You can read more in our docs [here](https://docs.pioreactor.com/user-guide/common-questions#why-does-my-optical-density-flatten-or-even-decrease-what-is-a-saturation-point).

I’m curious where you’ll find a Pioreactor with 30 deg angle though! 🙂

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**Author:** ![oni6969](https://forum.pioreactor.com/letter_avatar_proxy/v4/letter/o/aca169/32.png) [@oni6969](https://forum.pioreactor.com/u/oni6969)\
**Post date:** [March 3, 2024, 3:17pm UTC](https://forum.pioreactor.com/t/led-openings-holes/212/8 "2024-03-03T15:17:21Z")

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I am scaling it up to a 100 mL bottle 🙂

 ![Screenshot 2024-03-03 161440](https://forum.pioreactor.com/uploads/default/original/1X/d4068e405d0a9ffbe92f891c8f6d817b7b9ea9c0.png)

I’ll share it once finished testing

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**Author:** ![samunozg](https://forum.pioreactor.com/letter_avatar_proxy/v4/letter/s/e56c9b/32.png) [@samunozg](https://forum.pioreactor.com/u/samunozg)\
**Post date:** [July 13, 2025, 7:01pm UTC](https://forum.pioreactor.com/t/led-openings-holes/212/9 "2025-07-13T19:01:24Z")

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Hey @oni6969, any updates on this?