A sheer curtain can feel pleasantly private during the day and much less private once the room lights are on after dark. The fabric has not changed; the lighting relationship has. A daytime look from inside the room is therefore an incomplete test of the window treatment.
IKEA’s sheer-curtain guidance notes that silhouettes may remain visible from outside at night when indoor lights are on. Its window-solutions guide distinguishes light filtering from options intended to provide more substantial privacy. The performance still depends on the specific fabric, coverage and setting.
Test the situation you actually need
With permission and without intruding on anyone else, check the window from an ordinary outside viewing position after dark while the room is lit as usual. Have another person inside adjust the normal lamps. You are assessing your own room’s visibility, not looking into neighbouring properties.
Notice both the centre of the curtain and the edges. A denser fabric may still leave a direct view through a gap. Consider whether the treatment closes fully and whether the mounting arrangement suits the window’s shape.
If daytime light and evening privacy are both priorities, a layered arrangement may be useful: a sheer for the daylight effect and a suitable second covering for the hours when more privacy is wanted. Check that the hardware can support and operate the chosen layers without interference.
Do not equate a colour name with a privacy rating. A pale dense fabric and a dark open weave can behave differently, and photographs rarely show every lighting condition. Ask for the product’s actual description and test a sample where practical.
Choose the textile for the task it needs to perform. Sheers can provide a beautiful light-filtering layer, but the evening check tells you whether that layer is enough for the room’s real use.