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The midday sun beat down on the tennis court so brightly it was blinding.
Literal
Midday [genitive-の] sun [subject-が] tennis court [object-を] eye [also-も] blind [to-the-extent-ほどに] illuminated-up.
An image with three layered grammar points. (1) 目も眩む ('the eyes even get dizzy/blinded') is a set phrase for extreme brightness or dizziness — literally 'even the eyes spin,' with も adding the scalar 'even.' (2) ~ほどに ('to such an extent that') scales that phrase into a degree modifier for the next verb: 'illuminated to the extent that one was blinded.' (3) 照らしあげる is a compound verb: 照らす ('illuminate') + 上げる ('raise up, thoroughly'), where ~上げる intensifies and completes the action — 'shone intensely upon.' Together the sentence is a vivid sensory description of blinding midsummer sun.