How to measure intense ambient light

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RLM

Joined Feb 17, 2012
2
I am helping my HS freshman son in a science project to measure ambient light at different elevations. We have a friend in a high altitude (100,000 ft) balloon club who offered a 750 gram payload on a flight this spring! What a great opportunity. We bought a TAOS "light to voltage" photodiode TSL14S-LF and made the circuit at http://www.sciencebuddies.org/science-fair-projects/project_ideas/Elec_p037.shtml When pointed at the sky the output tops out at 4.5 V so I think that is full scale. I need ideas about how to change the circuit to get more dynamic range. Or maybe I need a different photodiode. Maybe we should use a photoresistor or something else? Thanks for the help!
Bob
 

ErnieM

Joined Apr 24, 2011
8,046
From what I quickly gathered on the TAOS part it is not adjustable.

You could start experimenting with various shades. Old sun glasses, two polarized plates (rotate till intensity OK), and things like that.
 

Markd77

Joined Sep 7, 2009
2,806
It shouldn't be at maximum even in full sunlight, it has a sensitivity of 16mV per (μW/cm^2) which means it should be about 2.1V in full sunlight (137mW/cm^2).
Have you got the load resistor of 10K connected?
 

Bernard

Joined Aug 7, 2008
5,560
Photographic film exposed to different degrees works well to adjust sensitivity-- as used to adjust sensitivity of LDR's in solar tracker.
 
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