The term Schachtlichte refers to an Oberlicht (skylight, rooflight). Schachtlichte is the minimum size in mm of the roof opening to allow the right amount of light into the room through the skylight/rooflight.
You can see one on page 16 of the pdf referred to in the web references.
lichte/Licht is often used with other words to indicate a minimum clear distance

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Note added at 19 hrs (2023-05-28 15:52:48 GMT)
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In the pdf I give as the reference Schachtlichte occurs with Oberlichte in plan on p 16. In this case they are rooflights allowing light to enter an underground room through the roof from ground level. There could be a "shaft" involved if the depth of roof slab and fill is appreciable. A shaft would be involved if you were getting light from a rooflight to a ground floor room through a roof space. So in this case "rooflight shaft minimum size 1132 mm" may be appropriate. Is that likely in your window spec case?
I came across this example first - 2 x Schachtlichte - one "a" and "b" applied to a chamber or manhole cover detail. The dimensions apply to the basic internal size of the chamber or manhole. I could not apply this directly to the context of windows or illumination. https://www.janssen-umwelttechnik.de/fileadmin/redakteur/pdf...
Passing thought - Could it be to do with solar tubes/tunnels, sun tubes, light pipes etc. "shafts" are involved in those.