“Over the past decade, luminaire measurement systems transitioned from sphere systems to gonio systems. This is due to the rise of various goniometric measurement solutions, the availability of LED luminaires, the use of architectural lighting design software, as well as evolutions in international standardization.
The international CIE S 025 standard, although based on existing regional standards from USA, Europe, China and Japan, does bring less restriction where possible and consequently allows the use of less complex goniometric systems.”
Pieter Kramer, Laser 2000