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Light pulse measurement equipment / circuit?

  1. Jan 19, 2015 #1
    I am not a classroom student but study what I feel like knowing. As such I don't have access to professional teachers to ask questions like this one. The reason I ask is that my daughter has epilepsy and pulsing lights cause seizures. It is my understanding that florescent lights actually pulse because of the AC current source. I thought that LED lighting would help but it seems like both the box store LED bulbs and the florescent bulb replacement for tube ceiling light also pulse. Christmas tree LED light strings have two halves that switch back and forth because of the AC applied.
    What I am looking for is a way to measure the pulse frequency of "ambient light" in a room. To measure the pulses of light from an external source. I am familiar with basic electronics and beginning to build "real world" interfaces. I am confident that I could build a circuit, but I don't currently have the knowledge to DESIGN my own device. If there is a device for sale that does what I am looking for that will work also. I would guess that I am looking to measure pulses from 0-600 pulses/second. Each ambient source could be a different frequency (color) of light and I don't think I would need to be able to measure that.

    If you can help, I sure would appreciate it.
    dmac257
     
  2. jcsd
  3. Jan 19, 2015 #2

    Drakkith

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    Have you tried CFL's, compact florescent lamps, with electronic ballasts? They are supposed to operated at around 10-20 kHz (10-20 thousand cycles per second), well above the 60 Hz (60 cycles per second) mains electricity frequency which causes noticeable flicker.
     
  4. Jan 19, 2015 #3
    My daughter has replaced all her lights in her home with CFL's and she is having more seizures but BECAUSE they are SUPPOSED to be much higher flicker rate they aren't SUPPOSED to aggravate seizure disorders. The issue seems to be worse and I can't find any ACTUAL information on the web about the flicker rate of the light from Sylvania or Panasonic (the ones she bought) . When asked, one replied that they were not aware of any issues with flickering causing seizures (covering their ass) and the other simply didn't reply. Other things seem to aggravate her like television and laptop/computer screens. What I would like to do is MEASURE the flickering in her home. SO I asked if someone knew of a device to measure the ambient light.

    dmac257
     
  5. Jan 20, 2015 #4

    jim hardy

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    Some people are more sensitive to that than others. Ive heard of a similar case.


    Here's a hobbyist thread unrelated to PF
    where some experimenters have measured flicker in CFL and LED bulbs. it's at of course twice line frequency which your daughter might well see..
    http://www.candlepowerforums.com/vb...ND-FLICKER&s=9129d7fe8a043b7e472b916868895c40
    http://www.candlepowerforums.com/vb/showthread.php?361354-CREE-BULBS-AND-FLICKER/page2

    They used homemade equipment
    that's mighty primitive but creative, and gave him rough comparisons of various bulbs.
    another guy there built a better instrument based on this device

    www.ams.com/eng/content/download/250427/976469/file/TSL257-E.pdf

    and posted these two measuements

    flicker.png


    and

    flicker.png


    That's at (edit) 50hz100 hz, twice power line frequency where he lives. In US it'd b 120hz. Whatever is a "Cree" it looks to have more powerline frequency flicker than incandescent.

    So if experimenters are building them, such instruments must exist in industry
    here's one
    http://www.westardisplaytechnologies.com/products/westar-optical-instruments/
    but i've no idea what it costs.

    Are you an experimenter who might piece together a home-brew instrument?
    Seems one could adapt a "Super Snooper" amplifier to use a photosensor instead of microphone...
    151204.jpg
    http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_151204_-1

    I'm obsolete, but today's experimenters would probably grab an Arduino or PC instead.

    Good luck to you, sir., and your daughter.
    old jim
     
    Last edited: Jan 20, 2015
  6. Jan 20, 2015 #5

    Baluncore

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    Photosensitive epilepsy is usually triggered by flashing with frequencies between 2 Hz and 55 Hz.

    All lamps, when functioning correctly, have frequencies greater than 100 Hz. Computer screens that display a different frame for say only half a second can also stimulate epilepsy.

    Fluorescent lamps sometimes flicker when they are starting and cold. CFL and LED lamps should not present that problem.

    If you can see the flicker in a lamp then that lamp may well be a trigger a seizure in an epileptic. If you cannot see or sense the flicker in a lamp then it is most unlikely to trigger a seizure.

    By turning your head or sweeping your eyes across a flickering lamp, you will see a series of bright and dark images as the image of a lamp passes across your visual field. If you cannot see that strobe effect then there should be no problem for an epileptic.
     
  7. Jan 20, 2015 #6
    I think my daughter is more sensitive than other sensitive people. She is even thinking of doing away with TV and computer .. even her I-Pod causes issues.. but of course we can't point to one cause.
    I had already read most of the candlepowerforums threads about flicker
    and hooked it to a speaker, but I don't know how they measured the sound frequency..I don't have an oscilloscope.
    I was thinking a reverse strobe scope .. instead of variable strobe to make a spinning device appear to stop and measuring the external device
    vary the speed of rotation of a fan until the flickering "ambient" light makes it appear to stand still .. ideas are easier than implementation.
    I am just getting to the point in my electronics hobby so that some devices are beginning to make sense..still far from the design it myself stage
    Probably way more than I can afford.

    I have and Arduino and just starting to experiment with making it do stuff. I was kinda hoping for someone to point me to a ready made circuit I could build to shave a month or two of experimenting on my own but that is how you learn. In the mean time I bought a couple of off the shelf LED light bulbs to disassemble and see how they tick. I already made a light that uses DC to supply the LED and installed it in her living room to see if that helps .. it is ugly but functional as an experiment.
    Thanks for your help Jim
    dmac257
     
  8. Jan 20, 2015 #7

    jim hardy

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    ahhhh electronics experimenters get accustomed to power supply hum and recognize it.
    They were looking for power line frequency. That's the mechanism that makes them flicker

    Here's a current trace from Wikipedia
    https://en.wikipedia.org/wiki/Compact_fluorescent_lamp

    800px-CFL_Positive_power.png

    What do you suppose the voltage across the lamp's filter capacitor looks like?
    Clearly when conduction begins it is less than line voltage
    and presumably it charges to power line's peak value because conduction continues until peak
    so i'm estimating from above picture that the filter capacitor delivers to the lamp's internal high frequency oscillator
    a voltage that swings from 74% to 100% of incoming power peak,
    in US that'd be maybe from 130 volts to 175 volts with a sawtooth shape.
    Like this only it sags clear down to 75% between peaks

    http://upload.wikimedia.org/wikipedia/en/thumb/7/7e/Smoothed_ripple.svg/400px-Smoothed_ripple.svg.png [Broken]
    so the high frequency oscillator because of its varying input voltage does not deliver constant power to the lamp's phosphors
    and light output follows , at twice line frequency.
    You probably knew that already.

    my point was - i think line frequency is your culprit
    probably the light, but maybe audio noise for the current is a series of high frequency bursts repeating at 120 hz

    That light sensor from candlepower forum is good into mid audio range , a few khz
    and peak sensitivity is down in the red (700 nm)
    (hardly ideal for quantifying flourescent light)
    so It probably under-reported variation in their LED and over-reported for the incandescent

    If i knew of a ready made instrument i'd suggest it.


    Good Man ! That's the logical first step.
    I trust you filtered your DC exceedingly well.

    Is there a difference with that DC lamp??

    sorry i cant be more help.

    I can see i'm going to have to learn Arduino.

    old jim,
    stuck in the vacuum tube days
     
    Last edited by a moderator: May 7, 2017
  9. Jan 20, 2015 #8

    berkeman

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    @dmac257 -- Sorry if you mentioned this already and I missed it, but is your daughter under a doctor's care for these seizures? It sounds like she should see a specialist, especially since you say that she seems to be sensitive to light with frequencies well above those in the published literature. I hope you find some good help, and perhaps some good medication that can ease these issues.
     
  10. Jan 23, 2015 #9
    my daughters issues are that the medications (she takes 4 different anti-seizure meds and LOTS of vitamins to replace what is depleted by the anti-seizure meds) are almost maxed out for her body weight and even though she IS under an specialist care, she still has several minor seizures a day. Even walking on the beach triggers seizures from reflections on mica in sand and the water so she is very sensitive to environmental lighting. Full disability doesn't give her much money so cutting cost meant getting CFL bulbs in all her lamps. She says she has more seizures now that the CFLs are installed, so I wanted to find a way to measure the different bulbs to see if it made a difference. If I can find info on which bulbs are better at filtering the flicker I would be happy. The manufacturers are very tight on this info cause they think i am trying to gather info for a law suit or something.
    dmac257
     
  11. Jan 23, 2015 #10
    The lamp I made is 4 LEDs sitting on top of a 6V battery with a styrofoam cup on top to "shade" the "bulbs" .. If I made or bought a DC power source I would have no way to MEASURE the DC ripple so I went with straight battery for the "test" light. It isn't very bright at all and I am working on a MUCH brighter one using high intensity LEDs.

    So far she has not noticed the difference because she is using other lights in her home.
    dmac257
     
  12. Jan 23, 2015 #11

    jim hardy

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    Most DMM's when selected to AC will only report the ripple

    most inexpensive analog meters won't do that trick
    but
    a good quality analog meter like Simpson 260 has a jack labelled OUTPUT, lower right
    Simpson-260-multimeter-vom-volt-ohm-meter-series-7P-img-1.jpg


    it connects to an internal capacitor in series with the meter
    to block DC
    so that you can use it in set for AC to measure power supply ripple.
     
  13. Jan 23, 2015 #12
    holy smoke, I haven't see a Simpson 260 in almost 30 years. do they still make them??
    dmac257
     
  14. Jan 24, 2015 #13

    jim hardy

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    Yes but they are high.

    I still have the Triplett 630 i bought new in 1964
    and a Simpson 260 i stumbled across in a pawn shop...
    they do show up on Ebay
     
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