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La Sagrada Familia can only light up (normal lights, not the lights used for special events) from Thursday to Saturday between 20:00 and 00:00 due a decree for light pollution made by the Generalitat.
I live 10 min walking from the Sagrada familia, and I can say that even if you go any day (even any from Sunday to Wednesday) at night you will be able to see it very well and take some nice pictures, of course you can have better quality when it's fully lighted.