Reverse Engineering A Real Candle

[cpldcpu] just can’t leave the mysteries of candles alone. We’ve covered his explorations of candle flicker LEDs before, but this time he’s set his sensors on the real thing. [cpldcpu] hooked a photodiode to his oscilloscope, pointed it at a candle flame, and recorded the result.

The first interesting observation was the candle slowly changed brightness, whether it was interacted with or not. Next he measured the effect when the flame was disturbed by small gusts of air. This produced a bright flicker with an oscillation at 5Hz before returning to steady state, which as [stygiansonic] mentioned in a the Hacker News comment, is a known phenomenon used in flame detectors. Neat! There’s even an equation:

Under normal gravity conditions, the flames have a well defined oscillation frequency which is inversely proportional to the square root of the burner diameter, D, and to a good approximation can be written as f » 1.5/D½, with D given in meters.

[cpldcpu] then compiled his measurements into a series of graphs and ultimately an animated gif comparing the candle steady state, a real candle’s flicker, and the flicker he recorded from a candle flickr LED. It’s surprising how different the fake is from the real thing. You can look at his measurements and code at his github.

[via Hacker News]

19 thoughts on “Reverse Engineering A Real Candle

  1. My own experiments with this have found that you have to take into account the position of the flame along the wick axis as it burns. A simple flicker is good, a flame that “jumps off the wick” a small distance and varies in length as a real one will do is better (from a very subjective standpoint). Also the color will vary both with position and movement as this happens (a real candle flame has quite a range of colors from blue to orange). A NeoPixel stick (or its low-budget equivalent) is a good starting point for experimentation.

  2. Very nice, and timely as one of my daughters has been working on an LED lamp with candle mode as one of the features. I am sure cpldcpu’s science is solid and it would be interesting to implement their findings but they have overlooked a characteristic of candle flames that my kid found helped with the realism, small changes in the black-body temperature of the light during flickering.

    Does anyone have a spectrograph so that they can record this from a real candle? I am sure she would be very appreciative to have some science to compare against her guesses.

  3. Does anyone else have a problem with the two vinculums in that equation (approximation)?
    f » 1.5/D½

    I mean why stop there when 1.5 is equal to 3 /2

    so f » 3/2/D1/2

    in maths the / in ½ has exactly the same meaning/function as the slash in 1.5/D it’s just that one is written the old way and one is written the new way.

    1. I think that’s an result of the limitations of the copy/paste. He said it’s the square root so I think the 1/2 was originally a superscript exponent (taken to the 1/2)

      It should be 1.5*√D or 1.5*sqr(D) if the comment doesn’t post correctly

  4. Really though, a proper candle does not flicker. You have to use fruity scented sissy candles. Big blocks of wax with a wick down the middle and no air flow. And if they flicker they make soot (fail to react all the carbon in the top white zone). If you have to have flicker, LEDs at least don’t make soot, at least not locally.

  5. I have a bag of red/yellow bicolor LEDs just itchin’ to become artificial candles (or, as I originally intended, a fake fireplace). Thanks to the suggestion of [M H] above, I’ll be able to use my nonshiny new spectrometer to figure out how to program them. Results will be posted.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.