•Energy
–joules, radiant flux (energy/unit time)
–watts (1 watt=1
joule/second)
•Angles
–steradians -
sphere radius r - circumference is 2pr2; the angle that intercepts
an arc r along the circumference is defined as 1 radian. (57.3 degrees) a sphere of radius r has a surface
area of 4pr2. One steradian is defined as the
solid angle which intercepts as area equal; to r2 on the sphere surface