[Laser] Can some explain Steradian please

[J Forster]

It'ws a measure of solid angle:

The solid angle subtended at the center of a hemisphere is 2*PI Seradians.

See:

http://en.wikipedia.org/wiki/Steradian

Best,
-John

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Paul Cianciolo wrote:

> Hello Folks,
>
> I wonder if there is some one out there in Laserland or LEDland, that can
> explain the term steradian in layman's terms.
>
> As the term applies to LED's and intensity.
>
> For example if we start with a "reference LED"
>
> And drive it with say 2 volts and 100 ma that equals 200 milliwatts of DC
> input power
> What that equates to in terms of light output at a given wavelength I don't
> know.
>
> But lets pick a wavelength 940 nm.
>
> Please forgive me if I use some terms in appropriately.
>
> So we have an LED with a set DC input level, and a set radiation pattern,
> Lambertian lets say.
>
> SO........
>
> There is a math formula that defines what a Steradian is and I assume that
> our reference LED illuminates with a given level.
>
> LEDs are made with all sorts of 1/2 power beam angles. for 160 deg to 3
> degs.  So if we put a lens in front of our reference LED and try to
> collimate the beam into a narrower 1/2 power angle, does that increase the
> mW/Sr?
>
> Is it as simple as looking for the LED with the highest mW/Sr for the
> "brightest" infrared LED?
>
> PauLC
> W1VLF
> http://www.rescueelectronics.com/