What is "irradiance"

irradiance \ir*ra"di*ance\ ([i^]r*r[=a]"d[i^]*ans), irradiancy \ir*ra"di*an*cy\ ([i^]r*r[=a]"d[i^]*an*s[y^]), n. [From irradiant.]

1. The act of irradiating; emission of rays of light.

2. That which irradiates or is irradiated; luster; splendor; irradiation; brilliancy.
   --Milton.

1660s, from irradiant (1520s), from Latin irradiantem (nominative irradians), present participle of irradiare (see irradiate). Related: Irradiancy (1640s).

n. 1 The act of irradiating; emission of rays of light. 2 That which irradiates or is irradiated; lustre; splendour; brilliancy. 3 (context physics English) The radiant power received by unit area of surface

In radiometry, irradiance is the radiant flux ( power) received by a surface per unit area. The SI unit of irradiance is the watt per square metre . The CGS unit erg per square centimetre per second is often used in astronomy. Irradiance is often called "intensity" in branches of physics other than radiometry, but in radiometry this usage leads to confusion with radiant intensity.

Spectral irradiance is the irradiance of a surface per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength. The two forms have different dimensions: spectral irradiance of a frequency spectrum is measured in watts per square metre per hertz (W·m·Hz), while spectral irradiance of a wavelength spectrum is measured in watts per square metre per metre (W·m), or more commonly watts per square metre per nanometre .

Irradiance is the fifth and final studio album by American progressive metal band Canvas Solaris. It was released in 2010.