Historical clue formulations

• Light unit — 2025-05-01
• Measure of brightness — 2025-02-05
• Bulb unit — 2022-12-06
• Light measurement — 2020-06-14
• Unit of brightness — 2020-05-10
• Light unit — 2019-12-27
• Unit of light — 2019-09-28
• Measure of light's brightness — 2019-08-05
• Projector unit — 2015-08-09
• Unit of light — 2014-04-15
• Photometry unit — 2014-01-04
• Light unit — 2013-12-21
• Measure of light — 2007-03-11
• Bulb unit — 2005-11-20
• Unit of light — 2000-06-05
• Light bulb unit — 1995-10-28