; "lux" is lumens / m^2

; (var 'symbol 'name 'units)

(var E "illuminance" 'lux)
(var Theta "luminous power" 'lumens)
(var I "pointance" 'candela)
(var Omega "solid angle" 'sterradians)

(eq Theta
    (* 4 pi I))

(eq E
    (/ Theta A)
    (/ (* I Omega) A)
    (/ (* I A) (* A (exp r 2)))
    (/ I (exp r 2)))

(eq Omega
    (/ A (exp r 2)))

(eq I
    (partial-derivative Theta omega))