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DiscoverCircuits.com -- Hobby Corner
Last Updated on:
Tuesday, November 29, 2011 08:14 PM
Hobby Circuits'
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More
Light Sensors |
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Light Intensity Monitor
designed by David Johnson, P.E. |
| For an on-going
consulting project, I had to determine the light output decay time of different
fluorescent lamps. I wanted to know how fast the light from a lamp dropped to a
low level, after current was interrupted in the lamp. I used a high voltage
transistor circuit to drive the lamps under test and used the hobby circuit below
to measure the decay time. |
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hobby circuit was a simple PIN photo diode connected to a transimpedance amp. The
electronic circuit has an upper frequency cutoff of around 500KHz. The output signal
was fed to an oscilloscope through a coax cable. |
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It turns out that typical cool white,
warm white and kitchen lamps decay on the order of 30 milliseconds, while aquarium and
full sunlight spectrum lamps are quite fast, down to about 40 microseconds or so. A
black lamp, with no phosphor at all, decayed to 10% the peak value in about 20
microseconds. Perhaps at some future date I will experiment with using some of these
powerful light sources to send data over a wide area, by encoding data in the
modulating signal to the lamp. |
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Click on Drawing Below to view PDF version of Schematic |
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