Horizontal or vertical slats mounted inside the glazing, tilted to cut direct sun out of the line of sight while keeping the room daylit. This is glare control, not heat control, and the distinction matters: the sun has already passed through the glass before interior slats intercept it, so the heat is already in the room. For summer solar gain the device has to be on the outside (see the fixed overhangs, brise-soleil and shade-sail entries under solar gain avoidance). What this solves is the case where glare itself is the problem, a screen or work surface facing a window, or a low evening sun on a west elevation, and it doubles as privacy control. Cheap, universally available, and retrofits to any window without touching the structure.
Note: Cost, carbon and footprint are rated against the other options for this same need, not in absolute terms.
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No sizing or quantities: how much a technique yields, and how much a household needs, both depend on the build and the people, so the catalogue compares options rather than dimensioning them. It carries no bill of materials and no build sequence, and it is written for an oceanic, clay-soil climate (Normandy, France). Regulatory notes are indicative and need confirming locally.