I have difficulties to compare different brightness data of the sky.(adsbygoogle = window.adsbygoogle || []).push({});

In older literature I found different measurements of the brightness density of the sky. Some of the results are shown in in m(vis)/deg^2 and others in asb. In order to compare the data in units of m(vis)/sterad, I proceeded as follows:

The asb values:

1 Lux / sr = asb * Pi

since 1 Lux corresponds to -14.18 m(vis)

1 asb = - 1 / Pi * 14.18 m(vis) / sr

for the conversion I calculate

m(vis)/sr value corresponds to -14.18 - 2.5*LOG10( Pi * asb value )

For m(vis)/deg^2 values:

m(vis)/sr value corresponds to m(vis)/deg^2 value - 2.5*LOG10( (180/Pi)^2 ) = m(vis)/deg^2 value - 8.79

The results show me that doing so is not correct! However, the difference of around. 2.67 m(vis)/sr indicates some where a missing factor of 4*Pi. In the conversion of the m(vis)/deg^2 values, a possible 4*Pi-factor in the LOG10-expression was omitted intentionally since the 'per degrees' are converted in 'per radians' and not for the full sphere.

Could some one please indicate me where I am doing wrong. Thank you.

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Need help: Brightness conversion

Can you offer guidance or do you also need help?

Draft saved
Draft deleted

**Physics Forums | Science Articles, Homework Help, Discussion**