# Flux per unit projected area per unit solid angle,

1. Sep 5, 2008

### Somefantastik

"flux per unit projected area per unit solid angle,"

$$L = \frac{\partial \Phi}{\partial \left(cos \Theta \right) \ \partial \Omega}$$

What is this quantity? I mean, I know it's "flux per unit projected area per unit solid angle," how does the math work?

I know it's not

$$\frac{\partial \Phi}{\partial (Acos \Theta)} \frac{\partial \Phi}{\partial \Omega}$$

2. Sep 5, 2008

### Somefantastik

well it's either a typo, or some weird convention where people don't follow the rules. I found a few pages later, a table, where the same quantity was given by

$$L = \frac{ \partial^{2} \Phi}{\partial(Acos \Theta) \ \partial \Omega}$$

Which of course, makes a heck of a lot more sense.

It's on page 6 of William Wolfe's intro to Radiometry :-/

3. Sep 5, 2008