• springBreeze

springBreeze

While reading a paper on optics, I came across "the radiance of the projector is 20 mW/cm2, expanding out onto an f/18 cone."

What does the "expand out onto an f/18 cone" part mean? I thought that radiance is just in units of power/area/steradians. What does f-number have to do with anything?

You just need to convert the f/# into solid angle:

http://calctool.org/CALC/phys/optics/NA_to_f

an f/18 is a numerical aperture of 0.028, which gives a cone half-angle of 0.028 radians, or 0.0024 steradians, if I've converted everything correctly.

Radiance is a measure of the amount of light that is emitted or reflected from a surface in a particular direction. It is commonly used in optics to describe the intensity of light in a specific direction.

2. What are the units for radiance?

Radiance is typically measured in units of watts per steradian per square meter (W·sr^-1·m^-2).

3. How is radiance different from luminance?

Radiance is a measure of the total amount of light emitted or reflected in a particular direction, while luminance is a measure of the perceived brightness of a surface as seen by an observer. Radiance takes into account the direction of light, while luminance does not.

4. What is the importance of radiance in optics?

Radiance is an important concept in optics because it helps us understand the behavior of light and how it interacts with different surfaces. It is used in various applications, such as remote sensing, imaging, and radiometry.