Exposure or fluency

The exposure of a surface for a duration \(\Delta t\) is given by

ζ = ∫ t 1 t 2 E ( t ) dt size 12{ζ= Int rSub { size 8{`t rSub { size 6{1} } } } rSup {`t rSub { size 6{2} } } {E left (t right ) ital "dt"} } {}

The exposure is expressed in joules \(( \text{Wm}^{-2})\).