*Notes*

dP | power, expressed in watts [W]; |

dA | surface, expressed in square metres [m^{2}]; |

E(t), E | irradiance or power density, the radiant power density per unit area upon a surface, generally expressed in watts per square metre (Wm^{-2} ). Values of E(t), E come from measurements or may be provided by the manufacturer of the equipment; |

H | radiant exposure: the time integral of the irradiance, expressed in joules per square metre (Jm-2); |

t | time, duration of the exposure, expressed in seconds [s]; |

λ | wavelength, expressed in nanometres [nm]; |

γ | limiting cone angle of measurement in field-of-view, expressed in milliradians [mrad]; |

γm | measurement field of view, expressed in milliradians [mrad]; |

α | angular subtense of a source, expressed in milliradians [mrad]; |

limiting aperture the circular area over which irradiance and radiant exposure are averaged; | |

G | integrated radiance: the integral of the radiance over a given exposure time expressed as radiant energy per unit area of a radiating surface per unit solid angle of emission, in joules per square metre per steradian [Jm^{-2} sr^{-1}]. |