From: pireddag@hotmail.com   
      
   On 2017-10-04 16:28, Phil Hobbs wrote:   
   > On 10/04/2017 04:29 AM, JTS wrote:   
   >> On 2017-10-04 03:55, malna.polya@gmail.com wrote:   
   >>> Hi All,   
   >>>   
   >>> I am working on a project: we have a light sensor with only around 40   
   >>> degrees field of view. Our goal is to measure the strength of the   
   >>> sunlight without introducing too much of a bias based on the time of   
   >>> the day - when the sun shines at a different angle. We want to keep   
   >>> the sensor stationary.   
   >>>   
      
   (cut)   
      
   >>>   
   >>> Another concern is to find a solution which doesn't filter out much of   
   >>> the light spectrum.   
   >>>   
   >>> Does anyone have any ideas on how to solve this challenge?   
   >>>   
   >>> Thank you in advance!   
   >>>   
   >>   
   >>   
   >> Other posters have more experience and might comment on this, but I have   
   >> got a feeling that the theorem of conservation of etendue makes what you   
   >> want impossible. If you want to decrease the angular spread of a source   
   >> (and this is what you want to do: a source emitting at different angles   
   >> for different times is the same as a source emitting at different angles   
   >> at the same time for what regards the theorem) then you have to increase   
   >> the area which the light crosses. I think this is what is happening in   
   >> the solution with a set of lenses.   
   >   
      
   >   
   > The OP can do pretty well with a non-imaging concentrator run backwards,   
   > i.e. small end towards the sky.  Of course it has to be smallish in   
   > order for the big end to fit the available detector, and there's still a   
   > cosine rolloff due to obliquity.   
   >   
      
      
   Yes, excellent: you need to decrease the area from where you collect the   
   light and you will be able to get light with the reduced angular   
   distribution at the detector.   
      
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