On Jul 22, 2005, at 2:47 AM, Lo Saeteurn wrote:
Hi,
Do anyone know how find how bright a point light is from a certain
distance (both linear and squared)?
Ex: If I'm 15 units away from a point light that has 500 brightness,
how bright would it be (both linear and squared attenuation)?
Actual light - or any radiation in the electromagnetic spectrum -
drops by the square of the distance, so:
I = P * (i / (d ^ 2))
where 'I' is the intensity 'd' units away from the point source, and
'i' is - I believe - the stated intensity in candlepower at the source,
and P is a proportionality constant to take into account other factors,
such as the sensitivity of the sensor, dust in the air, etc...
So, plugging in, you'd get:
I = (500) / (15 ^ 2) = 2.22 units of intensity (brightness). (ignoring
'P'; i.e. 'P' = 1)
Keep in mind that the perceived intensity may be less than this
number, depending on the sensitivity of the sensor to the wavelength(s)
in question, in which case, 'P' < 1!
Also, note that it doesn't apply to lasers/masers because of the
extreme directionality of the emitted radiation.
If it fell off as a straight linear function, then just remove the '^
2' from the equation, in which case, you'd get
I = P * (i / d)
or - again ignoring P -
I = (500 / 15)
I = 33.3 units of intensity
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William H Squires Jr
wsquires at satx dot rr dot com dot nospam <- remove the .nospam
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