In
radiometry
Radiometry is a set of techniques for measurement, measuring electromagnetic radiation, including visible light. Radiometric techniques in optics characterize the distribution of the radiation's power (physics), power in space, as opposed to phot ...
, radiant exposure or fluence is the
radiant energy ''received'' by a ''surface'' per unit area, or equivalently the
irradiance In radiometry, irradiance is the radiant flux ''received'' by a ''surface'' per unit area. The SI unit of irradiance is the watt per square metre (W⋅m−2). The CGS unit erg per square centimetre per second (erg⋅cm−2⋅s−1) is often used ...
of a ''surface,'' integrated over time of irradiation, and spectral exposure is the radiant exposure per unit
frequency or
wavelength, depending on whether the
spectrum is taken as a function of frequency or of wavelength. The
SI unit of radiant exposure is the
joule per square metre (), while that of spectral exposure in frequency is the joule per square metre per
hertz () and that of spectral exposure in wavelength is the joule per square metre per metre ()—commonly the joule per square metre per nanometre ().
Mathematical definitions
Radiant exposure
Radiant exposure of a ''surface'', denoted ''H''
e ("e" for "energetic", to avoid confusion with
photometric quantities), is defined as
where
*∂ is the
partial derivative
In mathematics, a partial derivative of a function of several variables is its derivative with respect to one of those variables, with the others held constant (as opposed to the total derivative, in which all variables are allowed to vary). Part ...
symbol;
*''Q''
e is the radiant energy;
*''A'' is the area;
*''T'' is the duration of irradiation;
*''E''
e is the irradiance.
Spectral exposure
Spectral exposure in frequency of a ''surface'', denoted ''H''
e,''ν'', is defined as
where ''ν'' is the frequency.
Spectral exposure in wavelength of a ''surface'', denoted ''H''
e,''λ'', is defined as
where ''λ'' is the wavelength.
SI radiometry units
See also
*
Exposure (photography)
*
Radiant energy
*
Irradiance In radiometry, irradiance is the radiant flux ''received'' by a ''surface'' per unit area. The SI unit of irradiance is the watt per square metre (W⋅m−2). The CGS unit erg per square centimetre per second (erg⋅cm−2⋅s−1) is often used ...
References
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Physical quantities
Radiometry