Illumination refers to the amount of light falling on a surface per unit area. It is typically measured in units like lux or foot-candles. Mean Hemispherical Candle Power (MHCP) is a term that is less commonly used today. It was a measurement used in the past to describe the directional distribution of light emitted by a light source. MHCP indicates how much light is emitted by a light source in all directions above a horizontal plane.
The term "candlepower" itself is an older unit of measurement for light intensity, representing the luminous intensity of a standard candle. Mean Hemispherical Candle Power was a way to describe the average light intensity over all angles in the upper hemisphere above a light source.
With advancements in lighting technology and the adoption of standardized units like lux and lumens, Mean Hemispherical Candle Power is not commonly used anymore. Instead, the terms and units like luminous flux (lumens), luminous intensity (candelas), and illuminance (lux) are used to describe various aspects of light and lighting systems in a more standardized and scientifically meaningful way.