Convert phot [ph] to meter-candle [m*c] Online | Free lllumination Converter

A Unit of Illuminance in Photometry

The phot (ph) is a unit of illuminance formerly used in photometry, representing the amount of luminous flux falling on a surface per unit area. One phot is equal to 10,000 lux (lm/m²), meaning it measures a very high level of illumination.

The phot was commonly used before the widespread adoption of the lux in the International System of Units (SI). It is derived from the Greek word "photos," meaning light, and was particularly useful for expressing strong light intensities, such as direct sunlight, which typically measures about 100,000 lux or 10 ph.

Though largely replaced by lux, the phot is still occasionally referenced in older scientific literature and certain industrial contexts. Because 1 phot equals 10,000 lux, it provides a convenient scale for quantifying intense lighting conditions without resorting to large numbers.

Understanding the phot unit helps in interpreting historical data and in fields where very bright light levels are relevant, such as outdoor lighting design, solar energy studies, and some photographic applications.

A Traditional Unit of Illuminance

The meter-candle (m·c) is a historical unit of illuminance that measures the luminous flux falling on a surface area of one square meter from a uniform point source with an intensity of one candlepower (now replaced by the candela) placed one meter away. It was used primarily before the international adoption of the lux as the standard unit for illuminance.

One meter-candle is roughly equivalent to one lux, since lux is defined as lumens per square meter. However, the meter-candle historically provided a more intuitive measure of illuminance based on the distance from a known light source, which was practical for early lighting calculations and designs.

While the meter-candle is largely obsolete today, replaced by the lux in most scientific and engineering applications, it remains a useful reference when interpreting older lighting standards, manuals, and specifications.

Understanding the meter-candle helps in grasping the evolution of lighting measurement units and appreciating the advances in photometric science that have led to more precise and standardized units.