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filtering out 120hz fluorescent light strobing

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  • krazunk
    Fluorescent lights blink at 120hz. Most of us don t notice, but for several thousand people in North America this is harmful. Some people with photosensitive
    Message 1 of 20 , May 5, 2004
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      Fluorescent lights blink at 120hz. Most of us don't notice, but
      for several thousand people in North America this is harmful. Some
      people with photosensitive epilepsy are felled by such lighting.
      They might be able to live more or less normal lives with the right
      medication, but only if they avoid flourescents. These lights are
      everywhere, so they cannot live normal lives.

      Several companies now sell active noise-cancelling headphones. It
      should be possible to create the optical equivalent - a wearable
      active device to counteract this 120hz strobing. This would be
      signifigantly more dificult than compensating for sound, but should
      be possible with existing technology.

      I can imagine several ways of doing this, but I am not technically
      apt enough to build even the easiest prototype: a baseball cap with
      sensor above and LEDs below driven out of phase with the ambient
      flicker.

      Such a project would be great for University students, if only I
      knew how to convince someone in Acadamy'

      I post this seeking ideas and hobbyists with more knowledge and
      equipment (right now I don't even have a scope to use).

      There might be enough people needing such a device to make
      developing one profitable. If not, it is still a fascinating
      challenge.

      Russ Fridley
      Beaverton, Or.
    • Dave Mucha
      ... but ... It ... technically ... Interesting. I wonder why they don t use opposing lights ? one strobes 10101010 and the other at 0101010 ? I know that
      Message 2 of 20 , May 5, 2004
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        --- In Electronics_101@yahoogroups.com, "krazunk" <krazunk@y...>
        wrote:
        >
        > Fluorescent lights blink at 120hz. Most of us don't notice,
        but
        > for several thousand people in North America this is harmful. Some
        > people with photosensitive epilepsy are felled by such lighting.
        > They might be able to live more or less normal lives with the right
        > medication, but only if they avoid flourescents. These lights are
        > everywhere, so they cannot live normal lives.
        >
        > Several companies now sell active noise-cancelling headphones.
        It
        > should be possible to create the optical equivalent - a wearable
        > active device to counteract this 120hz strobing. This would be
        > signifigantly more dificult than compensating for sound, but should
        > be possible with existing technology.
        >
        > I can imagine several ways of doing this, but I am not
        technically
        > apt enough to build even the easiest prototype: a baseball cap with
        > sensor above and LEDs below driven out of phase with the ambient
        > flicker.
        >
        > Such a project would be great for University students, if only I
        > knew how to convince someone in Acadamy'
        >
        > I post this seeking ideas and hobbyists with more knowledge and
        > equipment (right now I don't even have a scope to use).
        >
        > There might be enough people needing such a device to make
        > developing one profitable. If not, it is still a fascinating
        > challenge.
        >
        > Russ Fridley
        > Beaverton, Or.

        Interesting.

        I wonder why they don't use opposing lights ? one strobes 10101010
        and the other at 0101010 ?

        I know that offices with flourescents often have 25% of the lighting
        by incandescent. That creates a minimum lighing condition so the
        strobing is from something like 25% to 75% as it can never go less
        than 25% and the combination makes 100%. It use used to prevent
        headaches from workers.

        But, I think you are on to something there !
        and active filter, or sunglasses that absorb (adsorb?) the pulse
        peaks and release an even level... ?



        And this goes back to the Philadelphia Experiment.

        If we see in one small spectrum of light and we can make filters for
        every other spectrum, why is it that we cannot make filters to make
        things invisable ?

        I know we can make a filter to block everything from the UV band or
        the IR band....

        Or... maybe that filter IS avaible.... and we already have them.....
        eyelids.......

        naw.. too simple.

        Dave
      • Stefan Trethan
        ... My first thought was lcd shutter maybe . This would be EXTREMELY difficult to make. Although you CAN hear direction with only one ear it is rather a
        Message 3 of 20 , May 5, 2004
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          On Wed, 05 May 2004 18:11:16 -0000, krazunk <krazunk@...> wrote:

          >
          > Fluorescent lights blink at 120hz. Most of us don't notice, but
          > for several thousand people in North America this is harmful. Some
          > people with photosensitive epilepsy are felled by such lighting.
          > They might be able to live more or less normal lives with the right
          > medication, but only if they avoid flourescents. These lights are
          > everywhere, so they cannot live normal lives.

          My first thought was "lcd shutter maybe".

          This would be EXTREMELY difficult to make.
          Although you CAN hear direction with only one ear it is rather a
          one-dimensional
          thing, you only hear the amplitude.

          With the eyes you see a whole picture, with the flicker being in different
          places
          stronger and weaker. You can't just put another lighsource in, it would
          not compensate
          at the right places. Most likely you would make it much worse in most
          places of the
          viewing are.

          This is close to impossible to eradicade by superimposing another light
          source.

          The only possible electronic approach i can see would be a camera/monitor
          setup.
          Right now this would be awkward to wear, but in the very near future it
          might just
          be a matter of closed "sunglasses".

          (It is maybe strange to suggest but perhaps it would be possible for these
          individuals
          to live comfortable in another country having 50Hz, not sure what the
          "bandwith" of sensitivity
          is.)


          ST
        • Dave Mucha
          ... but ... Some ... right ... different ... would ... most ... light ... camera/monitor ... future it ... for these ... the ... There are other simplier
          Message 4 of 20 , May 5, 2004
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            --- In Electronics_101@yahoogroups.com, Stefan Trethan
            <stefan_trethan@g...> wrote:
            > On Wed, 05 May 2004 18:11:16 -0000, krazunk <krazunk@y...> wrote:
            >
            > >
            > > Fluorescent lights blink at 120hz. Most of us don't notice,
            but
            > > for several thousand people in North America this is harmful.
            Some
            > > people with photosensitive epilepsy are felled by such lighting.
            > > They might be able to live more or less normal lives with the
            right
            > > medication, but only if they avoid flourescents. These lights are
            > > everywhere, so they cannot live normal lives.
            >
            > My first thought was "lcd shutter maybe".
            >
            > This would be EXTREMELY difficult to make.
            > Although you CAN hear direction with only one ear it is rather a
            > one-dimensional
            > thing, you only hear the amplitude.
            >
            > With the eyes you see a whole picture, with the flicker being in
            different
            > places
            > stronger and weaker. You can't just put another lighsource in, it
            would
            > not compensate
            > at the right places. Most likely you would make it much worse in
            most
            > places of the
            > viewing are.
            >
            > This is close to impossible to eradicade by superimposing another
            light
            > source.
            >
            > The only possible electronic approach i can see would be a
            camera/monitor
            > setup.
            > Right now this would be awkward to wear, but in the very near
            future it
            > might just
            > be a matter of closed "sunglasses".
            >
            > (It is maybe strange to suggest but perhaps it would be possible
            for these
            > individuals
            > to live comfortable in another country having 50Hz, not sure what
            the
            > "bandwith" of sensitivity
            > is.)
            >
            >
            > ST


            There are other simplier choices.

            DC lights have no flicker.

            A face shield, like a motorcycle windshield would allow you to tint
            it and then have an interior light soruce.

            that would reduce the external effects considderably.

            Also, I understand you don't need lights when you are on a desert
            island..... drinks with those little umbrellas.......


            Dave
          • Stefan Trethan
            ... Yea guess what.. We are at the 400kg gorilly syndrome again.. (yea this one is a metric gorilla). I don t think you can install dc lights everywhere...
            Message 5 of 20 , May 5, 2004
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              > There are other simplier choices.
              >
              > DC lights have no flicker.
              >
              Yea guess what..
              We are at the 400kg gorilly syndrome again.. (yea this one is a metric
              gorilla).
              I don't think you can install dc lights everywhere...

              There is a new generation of fluorescent "choke" (no idea how you call it)
              coming.
              It uses higher frequency. will take decades to exchange a noticeable
              number.

              > A face shield, like a motorcycle windshield would allow you to tint
              > it and then have an interior light soruce.

              Uhu, and what would you see then besides your nose?
              What's up Dave, is it late at night or what? I mean you really
              have enough imagination to notice a dark shield with a light INSIDE it will
              not be favourable for seeing anything at all.....

              >
              > that would reduce the external effects considderably.

              Yea, external effects, right, let's call it "you won't see anything at
              all".

              > Also, I understand you don't need lights when you are on a desert
              > island..... drinks with those little umbrellas.......

              I think you had those drinks already today?(just joking).

              ST
            • Roy J. Tellason
              ... Here it s called a ballast . Early models were in fact just chokes, mostly. ... Actually, I think these are becoming pretty common, at least in new
              Message 6 of 20 , May 5, 2004
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                On Wednesday 05 May 2004 02:57 pm, Stefan Trethan wrote:
                > > There are other simplier choices.
                > >
                > > DC lights have no flicker.
                >
                > Yea guess what..
                > We are at the 400kg gorilly syndrome again.. (yea this one is a metric
                > gorilla).
                > I don't think you can install dc lights everywhere...
                >
                > There is a new generation of fluorescent "choke" (no idea how you call it)

                Here it's called a "ballast". Early models were in fact just chokes, mostly.

                > coming. It uses higher frequency. will take decades to exchange a noticeable
                > number.

                Actually, I think these are becoming pretty common, at least in new
                construction.
              • Dave Mucha
                ... metric ... call it) ... noticeable ... tint ... it will ... I didn t say I worked out all the bugs. : ) Just like a heads up display, if you had some level
                Message 7 of 20 , May 5, 2004
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                  --- In Electronics_101@yahoogroups.com, Stefan Trethan
                  <stefan_trethan@g...> wrote:
                  >
                  > > There are other simplier choices.
                  > >
                  > > DC lights have no flicker.
                  > >
                  > Yea guess what..
                  > We are at the 400kg gorilly syndrome again.. (yea this one is a
                  metric
                  > gorilla).
                  > I don't think you can install dc lights everywhere...
                  >
                  > There is a new generation of fluorescent "choke" (no idea how you
                  call it)
                  > coming.
                  > It uses higher frequency. will take decades to exchange a
                  noticeable
                  > number.
                  >
                  > > A face shield, like a motorcycle windshield would allow you to
                  tint
                  > > it and then have an interior light soruce.
                  >
                  > Uhu, and what would you see then besides your nose?
                  > What's up Dave, is it late at night or what? I mean you really
                  > have enough imagination to notice a dark shield with a light INSIDE
                  it will
                  > not be favourable for seeing anything at all.....



                  I didn't say I worked out all the bugs. : )

                  Just like a heads up display, if you had some level of non pulsating
                  light, the background levels would have less of an effect.

                  Remember we are talking about people who cannot venture outside of
                  their own house.

                  Wheelchairs and casts are also restrictive. the idea was that some
                  small measure of usefullness might be gained, not that this would be
                  magic.

                  Dave
                • Steve
                  ... But the objects further away won t be lit by the LEDs and will still flicker. Ears are not very directional, eyes are. A friend of mine was responsible for
                  Message 8 of 20 , May 5, 2004
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                    --- In Electronics_101@yahoogroups.com, "krazunk" <krazunk@y...> wrote:
                    >
                    > Fluorescent lights blink at 120hz. Most of us don't notice, but
                    > for several thousand people in North America this is harmful. Some
                    > people with photosensitive epilepsy are felled by such lighting.
                    > They might be able to live more or less normal lives with the right
                    > medication, but only if they avoid flourescents. These lights are
                    > everywhere, so they cannot live normal lives.
                    >
                    > Several companies now sell active noise-cancelling headphones. It
                    > should be possible to create the optical equivalent - a wearable
                    > active device to counteract this 120hz strobing. This would be
                    > signifigantly more dificult than compensating for sound, but should
                    > be possible with existing technology.
                    >
                    > I can imagine several ways of doing this, but I am not technically
                    > apt enough to build even the easiest prototype: a baseball cap with
                    > sensor above and LEDs below driven out of phase with the ambient
                    > flicker.

                    But the objects further away won't be lit by the LEDs and will still
                    flicker. Ears are not very directional, eyes are.

                    A friend of mine was responsible for an entire building replacing
                    their fluorescent lights because of that flicker. He suffers from
                    migraines and discovered that it depends on the lighting he was under.

                    The office building had (of course) the cheapest fluorescent tubes
                    installed. He built a circuit to detect the amount of flicker to
                    illustrate the difference from one brand of tube to another.

                    Some fluorescent tubes have a longer persistence. They replaced all
                    the flickering tubes with long persistence tubes. Sick days due to
                    migraines were reduced significantly.

                    Of course, he was one of the owners and on the board of directors or I
                    doubt they'd have listened.

                    The new high frequency "ballasts" help, but cheap electronic ballasts
                    still flicker at 120Hz.

                    Alien Steve
                  • Richard Mustakos
                    Could you make a set of LCD sunglasses that flickered at some freq. that gives a less than horrible beat freq. with 120 Hz? I agree that anything with active
                    Message 9 of 20 , May 5, 2004
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                      Could you make a set of LCD sunglasses that flickered at some freq. that gives a less than horrible beat freq. with 120 Hz?
                      I agree that anything with active illumination just would not work - even if actively controlled.  Unless you carried around a set of actively controlled 1500 watt halogens work lamps.  If they respond fast enough.  Which I doubt, or they would be dumping 120 Hz flicker as well!
                      How do you calc beat freq.? Is it F1-F2?  Nobody responded on sensitivity ranges, so it's hard to find a suitable Freq. range.
                      On Wednesday 05 May 2004 02:57 pm, Stefan Trethan wrote:
                        
                      There are other simplier choices.
                      
                      DC lights have no flicker.
                            
                      Yea guess what..
                      We are at the 400kg gorilly syndrome again.. (yea this one is a metric
                      gorilla).
                      I don't think you can install dc lights everywhere...
                      
                      There is a new generation of fluorescent "choke" (no idea how you call it)
                          
                      Here it's called a "ballast".  Early models were in fact just chokes,  mostly.
                      
                        
                      coming. It uses higher frequency. will take decades to exchange a noticeable
                      number.
                          
                      Actually,  I think these are becoming pretty common,  at least in new 
                      construction.
                      
                        

                    • JanRwl@AOL.COM
                      Photonic capacitors? Polarized like Electrolytics? Spock! Help us!
                      Message 10 of 20 , May 5, 2004
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                        Photonic capacitors?    Polarized like Electrolytics?  Spock!  Help us!
                      • JanRwl@AOL.COM
                        In a message dated 5/5/2004 1:45:12 PM Central Standard Time, stefan_trethan@gmx.at writes: This is close to impossible to eradicade by superimposing another
                        Message 11 of 20 , May 5, 2004
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                          In a message dated 5/5/2004 1:45:12 PM Central Standard Time, stefan_trethan@... writes:
                          This is close to impossible to eradicade by superimposing another light source.
                           
                          What about half the lights connected to ONE phase, and the other half connected to the OTHER phase?  Too complicated for Union electricians?
                        • JanRwl@AOL.COM
                          In a message dated 5/5/2004 1:59:33 PM Central Standard Time, stefan_trethan@gmx.at writes: this one is a metric gorilla). Technical question: Would a metric
                          Message 12 of 20 , May 5, 2004
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                            In a message dated 5/5/2004 1:59:33 PM Central Standard Time, stefan_trethan@... writes:
                            this one is a metric gorilla).
                             
                            Technical question:  Would a metric gorilla have to purchase his flourescent tubes using Euro currency? 
                          • Anthony Toft
                            ... Any idea what the circuit looked like? a photodiode and resistor in voltage divider type of thing? Or something more elaborate? This might be amusing to
                            Message 13 of 20 , May 5, 2004
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                              > The office building had (of course) the cheapest fluorescent tubes
                              > installed. He built a circuit to detect the amount of flicker to
                              > illustrate the difference from one brand of tube to another.

                              Any idea what the circuit looked like? a photodiode and resistor in
                              voltage divider type of thing? Or something more elaborate?

                              This might be amusing to investigate, at home, work etc.


                              --
                              Anthony Toft <toftat@...>
                            • Stefan Trethan
                              ... no, he is so big he needs not to pay;-) st
                              Message 14 of 20 , May 5, 2004
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                                On Wed, 5 May 2004 23:45:48 EDT, <JanRwl@...> wrote:

                                > In a message dated 5/5/2004 1:59:33 PM Central Standard Time,
                                > stefan_trethan@... writes:
                                > this one is a metric gorilla).
                                >
                                > Technical question: Would a metric gorilla have to purchase his
                                > flourescent
                                > tubes using Euro currency?

                                no, he is so big he needs not to pay;-)

                                st
                              • Stefan Trethan
                                On Wed, 05 May 2004 23:55:26 -0400, Anthony Toft ... you need to ac couple it to get flicker. but then it is not relative. you most
                                Message 15 of 20 , May 5, 2004
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                                  On Wed, 05 May 2004 23:55:26 -0400, Anthony Toft <toftat@...>
                                  wrote:

                                  >> The office building had (of course) the cheapest fluorescent tubes
                                  >> installed. He built a circuit to detect the amount of flicker to
                                  >> illustrate the difference from one brand of tube to another.
                                  >
                                  > Any idea what the circuit looked like? a photodiode and resistor in
                                  > voltage divider type of thing? Or something more elaborate?
                                  >
                                  > This might be amusing to investigate, at home, work etc.
                                  >
                                  >

                                  you need to ac couple it to get flicker. but then it is not relative.
                                  you most likely want ficker in % of light.
                                  One way is to build a maximum detector, and a minimum detector.
                                  (2 opv circuits). then you can somehow display the percentage.
                                  the time constant would be a few periods of the 60hz.

                                  ST
                                • Steve
                                  ... But... that s still 120Hz flicker. Now instead of one fluorescent flickering once on each pos and neg cycle, you have two flickering each on opposite half
                                  Message 16 of 20 , May 6, 2004
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                                    --- In Electronics_101@yahoogroups.com, JanRwl@A... wrote:
                                    > In a message dated 5/5/2004 1:45:12 PM Central Standard Time,
                                    > stefan_trethan@g... writes:
                                    > This is close to impossible to eradicade by superimposing another light
                                    > source.
                                    >
                                    > What about half the lights connected to ONE phase, and the other half
                                    > connected to the OTHER phase? Too complicated for Union electricians?

                                    But... that's still 120Hz flicker. Now instead of one fluorescent
                                    flickering once on each pos and neg cycle, you have two flickering
                                    each on opposite half cycles.

                                    Only now instead of just flickering at 120Hz, the direction of the
                                    light is changing at 60Hz.

                                    Wear sunglasses inside, but make sure they are blue-blockers or the
                                    lens is red. Seriously.

                                    Your eyes respond much more slowly at lower light levels, and more
                                    slowly to light at the red end of the spectrum. So if you artificially
                                    lower and redden the light level, the flicker is less apparent.

                                    Amiga computer users had problems with flicker when set to some screen
                                    modes, and short of adding a scandoubler, the fixes all did ultimately
                                    the same thing- reduced the light level. One fix was to simply turn
                                    down the brightness on your monitor, another was a sheet of smoked
                                    plexiglass, and I did see people suggesting just putting on sunglasses.

                                    There is a type of 3D for movies and TV that don't use the red/green
                                    lenses. They had a few sitcoms do 3D episodes a few years back and
                                    they looked fine without the glasses. The glasses just had one lens
                                    darkened a bit, so that eye responded more slowly, and moving objects
                                    would appear to have a different parallax.

                                    So something moving right to left appeared closer than something not
                                    moving, or moving left to right.

                                    I recall one had the background scrolling to the right and the
                                    characters running along so they appeared still on the screen. It
                                    worked, the inside of the screen looked like a little diorama as long
                                    as things were moving.

                                    Alien Steve
                                  • Steve
                                    ... Probably just a phototransistor and resistor connected by DC blocking capacitor to an amplified AC voltmeter. A phototransistor should be more than fast
                                    Message 17 of 20 , May 6, 2004
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                                      --- In Electronics_101@yahoogroups.com, Anthony Toft <toftat@c...> wrote:
                                      > > The office building had (of course) the cheapest fluorescent tubes
                                      > > installed. He built a circuit to detect the amount of flicker to
                                      > > illustrate the difference from one brand of tube to another.
                                      >
                                      > Any idea what the circuit looked like? a photodiode and resistor in
                                      > voltage divider type of thing? Or something more elaborate?
                                      >
                                      > This might be amusing to investigate, at home, work etc.

                                      Probably just a phototransistor and resistor connected by DC blocking
                                      capacitor to an amplified AC voltmeter. A phototransistor should be
                                      more than fast enough for this.

                                      Alien Steve
                                    • Scott Thompson
                                      Yes, it would seem that this approach would be a simple detector. I would recommend using an oscilloscope, though, and one would be able to see the amount of
                                      Message 18 of 20 , May 6, 2004
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                                        Yes, it would seem that this approach would be a simple detector.  I would recommend using an oscilloscope, though, and one would be able to see the amount of "ripple" present under differing lighting conditions (the AC component).
                                         
                                        Best,
                                        Scotty
                                         
                                         
                                        ----- Original Message -----
                                        From: Steve
                                        Sent: 5/6/2004 07:53:55
                                        Subject: [Electronics_101] Re: filtering out 120hz fluorescent light strobing

                                        --- In Electronics_101@yahoogroups.com, Anthony Toft <toftat@c...> wrote:
                                        > > The office building had (of course) the cheapest fluorescent tubes
                                        > > installed. He built a circuit to detect the amount of flicker to
                                        > > illustrate the difference from one brand of tube to another.
                                        >
                                        > Any idea what the circuit looked like? a photodiode and resistor in
                                        > voltage divider type of thing? Or something more elaborate?
                                        >
                                        > This might be amusing to investigate, at home, work etc.

                                        Probably just a phototransistor and resistor connected by DC blocking
                                        capacitor to an amplified AC voltmeter. A phototransistor should be
                                        more than fast enough for this.

                                        Alien Steve


                                      • Stefan Trethan
                                        On Thu, 6 May 2004 15:18:08 -0700, Scott Thompson ... Yea, on a scope you would see how much is DC and how much AC light. I think it is important to know how
                                        Message 19 of 20 , May 7, 2004
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                                          On Thu, 6 May 2004 15:18:08 -0700, Scott Thompson
                                          <electronguy@...> wrote:

                                          > Yes, it would seem that this approach would be a simple detector. I
                                          > would recommend using an oscilloscope, though, and one would be able to
                                          > see the amount of "ripple" present under differing lighting conditions
                                          > (the AC component).
                                          >
                                          > Best,
                                          > Scotty
                                          >

                                          Yea, on a scope you would see how much is DC and how much AC light.
                                          I think it is important to know how much DC light there is, because
                                          the percentage is what you see i guess.

                                          Maybe a multimeter will do, with dc and ac range.

                                          ST
                                        • Steve
                                          That s what the AC voltmeter is for. An OpAmp, diode, and small analog meter would do it, and be much more portable than a scope. Of course, there s the
                                          Message 20 of 20 , May 7, 2004
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                                            That's what the AC voltmeter is for. An OpAmp, diode, and small analog
                                            meter would do it, and be much more portable than a 'scope.

                                            Of course, there's the coolness factor of looking at the waveform. ;')

                                            Alien Steve

                                            --- In Electronics_101@yahoogroups.com, "Scott Thompson"
                                            <electronguy@e...> wrote:
                                            > Yes, it would seem that this approach would be a simple detector. I
                                            would recommend using an oscilloscope, though, and one would be able
                                            to see the amount of "ripple" present under differing lighting
                                            conditions (the AC component).
                                            >
                                            > Best,
                                            > Scotty
                                            >
                                            >
                                            > ----- Original Message -----
                                            > From: Steve
                                            > To: Electronics_101@yahoogroups.com
                                            > Sent: 5/6/2004 07:53:55
                                            > Subject: [Electronics_101] Re: filtering out 120hz fluorescent light
                                            strobing
                                            >
                                            >
                                            > --- In Electronics_101@yahoogroups.com, Anthony Toft <toftat@c...>
                                            wrote:
                                            > > > The office building had (of course) the cheapest fluorescent tubes
                                            > > > installed. He built a circuit to detect the amount of flicker to
                                            > > > illustrate the difference from one brand of tube to another.
                                            > >
                                            > > Any idea what the circuit looked like? a photodiode and resistor in
                                            > > voltage divider type of thing? Or something more elaborate?
                                            > >
                                            > > This might be amusing to investigate, at home, work etc.
                                            >
                                            > Probably just a phototransistor and resistor connected by DC blocking
                                            > capacitor to an amplified AC voltmeter. A phototransistor should be
                                            > more than fast enough for this.
                                            >
                                            > Alien Steve
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