Undergrad IRAS Filter Profile: Computing ##\lambda_{mean}##

[tryingtolearn1]

TL;DR

IRAS filter profile

I am looking at the following IRAS filter profile IRAS Filter Profile and I am wondering how they computed $\lambda_{mean}$? They provided the following equation below but what is $T(\lambda)$ and $\lambda$?

 

[DrStupid]

Just a guess: T = transmittance and lambda = wavelength.

 

[tryingtolearn1]

Just a guess: T = transmittance and lambda = wavelength.

thanks but where did they get the transmittance?

 

[DrStupid]

thanks but where did they get the transmittance?

Something like that is usually measured. Here are the data:

https://irsa.ipac.caltech.edu/IRASdocs/exp.sup/ch2/tabC5.html

 

[mathman]

The equation itself is a mathematical expression for the mean value of T, whatever T is.