Wikipedia's Photometer article states three photometer types (Rumford's, Ritchie's, and shadow-extinction types) were already in common use by 1861, but names no invention year or event for the instrument itself. The existing invented edge already credits Benjamin Thompson (Count Rumford), but neither his own Wikipedia biography nor the Photometer or Photometry (optics) articles state a year. A web search found a plausible date, Rumford's 1794 paper in Philosophical Transactions vol. 84, but the corroborating page (Citizendium) returned HTTP 403 and was not visited, so it is not citable under the quote-capture duty.
What would resolve this A fetchable, quotable page (not blocked) that states the year Rumford, Ritchie or an earlier figure such as Bouguer or Lambert first built or described a working photometer, ideally naming the specific publication (Rumford's 1794 Philosophical Transactions paper is the leading candidate).
OpenHistory of sciencePhotometer (Wikipedia)