Illumination device known as the candela
In the world of science and technology, precision is key, and this is especially true when it comes to the measurement of light. The Measurement Standards Laboratory of New Zealand (MSL) plays a crucial role in ensuring that operating theatres are bright enough for surgeons to see their patients clearly.
On May 20, 2019, the International System of Units (SI) underwent a significant redefinition, and the candela, the unit of luminous intensity, was no exception. The candela is defined via the luminous efficacy of monochromatic radiation at a frequency of 540 × 10¹² Hz (540 THz), which corresponds to monochromatic green light at about 555 nanometers. This frequency was chosen because it lies near the peak of the human eye's photopic (daylight) luminous efficiency curve, making it the most sensitive to light at this frequency.
The choice of 540 × 10¹² Hz balances physical precision with perceptual relevance, defining luminous intensity in terms of light that the human eye perceives with maximum efficiency. The candela is defined to be as bright as a standard candle, and the constant conversion factor K, equal to 683 cd sr W at 540 x 10 Hz, is used to define the candela. Kcd, the constant unit used to define the candela, is a conversion factor for the original or absolute power divided by the power of that source that is perceived by the eye.
Peter Saunders and Farzana Masouleh of the MSL presented the redefinition of the SI at the Faculty of Engineering, Auckland University, at a location called Unleash Space. The presentation was filmed by Jonathon Potton of Chillbox Creative, and the video clip serves as a recording of this important event.
The MSL has also produced videos to share the story of metrology development, shedding light on the intricate process of defining and redefining units of measurement. These videos serve as a testament to the MSL's commitment to advancing science and technology through precise measurement.
Scientists at the Measurement Standards Laboratory of New Zealand (MSL) recognize the importance of balance, as demonstrated by the choice of 540 × 10¹² Hz for the candela's definition, which ensures physical precision aligns with perceptual relevance in health-and-wellness contexts such as operating theatres. Furthering their dedication to the advancement of science and technology, they've also shared insightful videos on metrology development in the field of fitness-and-exercise, essentially teaching the world about the intricate process of defining and redefining units of measurement.
