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Re: Solid Angles
The steradian is a unit of measure of solid angles that is expressed
as the solid angle subtended at the center of the sphere by a portion
of the surface whose area is equal to the square of the radius of the
sphere.
Hope this may help in the discussion.
Thanks,
> Date: Thu, 31 Aug 95 13:57:41 -0500
> Reply-to: radsafe@romulus.ehs.uiuc.edu
> From: "GORDON MILLER" <gordon_miller@lccmail.ocf.llnl.gov>
> To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
> Subject: Re: Solid Angles
> 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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> From: Bernard L Cohen <blc+@pitt.edu>
> To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
> Subject: Re: Solid Angles
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>
>James H. Ogden, Jr., Administrator
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