Hi, Asher,
60 mm above the central light.
I assume by that you mean 60 mm based on the pixel count of the image as posted, considered under the 72 px/in resolution value in the file header?
That would be just about 1/3 of the image height. Is that what you mean? (Based on 72 px/in, the 520 px height of the posted image is equivalent to 183 mm.)
That would probably be different to someone editing the image at original resolution (that is, in terms of pixel dimensions, not the "resolution indicator" value, which will probably be 72 px/in in both cases, meaningless in both).
If the original image were, for example, 2080 px high, and carried the "customary" resolution indicator value, 72 px/in, then the crop you suggest would be the top 241 mm.
Thais is why it is so dangerous to speak of crops in terms of dimensions (mm or inches), or even in terms of pixels.
Much better (to avoid all the potential problems in this areas) would be to say, "I suggest you crop off the top 30%".
Just to play with you, the following images are all 400 px x 795 px. But, on the basis on which I suspect you are working, this one is 10 mm high:
This one is 22.4 mm high:
This one is 280 mm high:
And we wonder why some people don't trust accountants!
Best regards,
Doug