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Subject: Re: [Homebrew_PCBs] Measured light reception from 10W LED according to distance from centre

From: Robin Whittle <rw@...>
Date: 2013-09-19

Hi Slavko,

You wrote:

> Robin can you test what time takes if the led is just 1 cm above
> (instead 34) board?

The area covered by the ligh is 1 / (34 x 34) of whatever it is at cm so
the time scales in the same way.

My exposure tests were at 30cm and I guess that somewhere between 40 to
80 seconds would be ideal. If we assume 60 seconds, then the time to
get the same exposure at 1cm would be:

60 / (30 ∗ 30) = 62 milliseconds

> I know the area will be small but I'm just interested how big efect the
> distance have on time?
> If source is point then relation is square from distance but the led
> isn't point source...

For a photoplotter you would have quite a different optical arrangement
from simple radiant light hitting the Riston.

- Robin