I work for a company that installs film studios. Our client have insisted that they retain the floor-to-ceiling windows in the studio space, to use as an alternative background to film against. For this to be possible, the windows must be covered in a "neutral density" (ND) gel - an adhesive sheet that absorbs light evenly without applying a colour tint.

The building owners have stepped in and asked that we provide calculations to prove that this won't cause thermal stress that could damage the windows, and are holding up work until we can provide this.

In this context, an estimated value would be fine. The properties of the glass can be assumed to be typical for office windows.

The studio is situated in the United Kingdom and is south-facing. The ND gel we're installing is 0.6. It reduces light by two stops, which is to say the amount of light is halved twice.

  • $\begingroup$ Seen DG windows fail due to uneven thermal loading - like shading etc, or even cupboards inside too close to the window. So an evenly applied coating should not have any affect - applied a film to reduce UV entry into a tiny house which works well (TG windows), BUT finding someone to sign off on that might prove difficult... $\endgroup$
    – Solar Mike
    Commented Aug 14, 2023 at 12:59


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