Most of those are fixed light source-detector , so it can only monitor the change of blood oxygen metabolizing in a certain depth.

广泛采用的光源与探测器间距固定的装置，只能反映组织特定深度的血氧信息；

youdao

Buddha of Fixed light. It is told that when he was born his body is surrounded with all lights.

燃灯佛，相传其出生时身边一切光明如灯。

youdao

However, in baby Millie's case there was no need to put her asleep, and that her pupils were fixed and did not respond to light.

BBC: Barry McCarney

He left it on a fixed aperture, so that as the light faded, the exposure got ever longer.

BBC: Cameras to capture a road trip

However, for the past few weeks it has been lit up after engineers fixed the fault and ran a reduced light display.

BBC: City of Culture art installation finally gets switch on