Re: Solid Angles

["GORDON MILLER" <gordon_miller@lccmail.ocf.llnl.gov>]

        Reply to:   RE>>Solid Angles
A formal definition of steradian I have seen is (2*arctan(radius of illuminated
or glowing area/distance between lit or glowing area and observer))^2.

The simple radian angle is 2*arctan(radius of illuminated or glowing
object/distance between lit or glowing area and observer)

A crude definition of steradians, useful for laser work, is the area of the lit
or glowing area divided by the square of the distance between lit or glowing
area and observer.

A crude definition of radians, suitable for laser work, is the long dimension
of a lit or glowing area/distance between lit or glowing area and observer.

There are 4 pi steradians in a sphere, 2 pi radians in a circle.

You could be talking about viewing an area lit by a laser or viewing an array
of bright lamps or lasers covering a surface or viewing within the beam of some
source laser or otherwise and looking at the source.

The Z136.1-1993 standard makes no use of steradians (they use extended source
correction factors instead and radian units), but ACGIH still uses steradians
for non-coherent sources of optical radiation as well as radians.

--------------------------------------
Date: 8/31/95 10:30 AM
To: GORDON MILLER
From: radsafe@romulus.ehs.uiuc.edu
It seems to me that the units could be watts/square meter or watts per 
steradian,but not both

On Wed, 30 Aug 1995, Alex Zapantis wrote:

> G'day All,
> 
> Could someone please explain the physical meaning of the unit:
> 
>          Watts per square metre per steradian
> 
> It's the "per steradian" which I am having trouble with.
> 
> In case you are wondering, this question is related to LASER safety.
> 
> Regards
> 
> 
> 
>                         Alex Zapantis
>                         Radiation Safety Officer                             
 
>                         Queensland University of Technology          
>                         Health & Safety Section                             
>                         Locked Bag No.2
>                         Red Hill Qld 4059
>                         AUSTRALIA
> 
>                         Ph     : 61 7 864 3566
>                         fax     : 61 7 864 3993
>                         email  : a.zapantis@qut.edu.au
> 
> 

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Subject: Re: Solid Angles
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