Tweak documentation wording

src/Illuminance.elm

@@ -10,7 +10,7 @@ surface: [luminous flux](LuminousFlux) per unit area. It is measured in
 Illuminance is useful as a measure of how brightly a surface is lit. For
 example, on an overcast day, outside surfaces have an illuminance of
 approximately 1000 lux; inside an office might be more like 400 lux and under a
-full moon might be 0.2 lux.
+full moon might be only 0.2 lux.
 
 [wp-illuminance]: https://en.wikipedia.org/wiki/Illuminance
 [wp-lux]: https://en.wikipedia.org/wiki/Lux>

src/Luminance.elm

@@ -6,11 +6,11 @@ module Luminance exposing
 {-| [Luminance][wp-luminance] is [luminous intensity](LuminousIntensity) per
 unit area or equivalently [illuminance](Illuminance) per [solid
 angle](SolidAngle), and is measured in [nits][wp-nits] (or, to use standard SI
-terminology, candelas per square meter). Luminance is often used to describe the
-brightness of a particular surface as viewed from a particular direction; for
-example, a computer monitor might be described as having a brightness of 300
-nits (but that would likely only be true when viewing straight on instead of at
-an angle).
+terminology, candelas per square meter - the two terms are equivalent).
+Luminance is often used to describe the brightness of a particular surface as
+viewed from a particular direction; for example, a computer monitor might be
+described as having a brightness of 300 nits (but that would likely only be true
+when viewing straight on instead of at an angle).
 
 [wp-luminance]: https://en.wikipedia.org/wiki/Luminance
 [wp-nits]: https://en.wikipedia.org/wiki/Candela_per_square_metre

src/LuminousFlux.elm

@@ -2,8 +2,11 @@ module LuminousFlux exposing (Lumens, LuminousFlux, lumens, inLumens)
 
 {-| A `LuminousFlux` value represents the total amount of light emitted by a
 light source. You can think of it as roughly "photons per second", although
-[it's a bit more complicated than that][wp-luminous-flux]. Luminous flux is
-stored in [lumens][wp-lumen].
+[it's a bit more complicated than that][wp-luminous-flux].
+
+Luminous flux is stored in [lumens][wp-lumen]. It's often used to describe the
+total output of a light bulb; for example, a 50 watt incandescent bulb and a 6
+watt LED bulb might each have an output of 400 lumens.
 
 [wp-luminous-flux]: https://en.wikipedia.org/wiki/Luminous_flux
 [wp-lumen]: https://en.wikipedia.org/wiki/Lumen_(unit)

src/SolidAngle.elm

@@ -120,8 +120,8 @@ inSquareDegrees solidAngle =
 
 {-| Find the solid angle of a cone with a given tip angle (the angle between two
 opposite sides of the cone, _not_ the half-angle from the axis of the cone to
-one of its sides). A one degree cone has a solid angle of approximately π/4
-square degrees, similar to how a circle of diameter 1 has an area of π/4:
+its side). A 1 degree cone has a solid angle of approximately π/4 square
+degrees, similar to how a circle of diameter 1 has an area of π/4:
 
     SolidAngle.conical (Angle.degrees 1)
         |> SolidAngle.inSquareDegrees