Interference of White Cree XP-G2 Emitter with 635nm laser?

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kennybobby's picture
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Interference of White Cree XP-G2 Emitter with 635nm laser?

This is an interesting problem that somebody here might have a clue, it involves interference with a 635nm laser range finder by a white Cree XP-G2 emitter in an art exhibit.

Here are some sentences about the problem, additional details are described here, range interruptus

modern art installation…a lingering problem with a piece where we levitate ping pong balls in glass tubes using programmed computer fans. We animate them into rolling sine waves etc. We achieve precise placement by repurposing a laser range finder and aiming it from the underside up towards the ball. This information is then fed back to correlate with the intended data value in our programming to place it precisely where we want it to be. This all works perfectly. The problem lies in the fact that all of these tubes are illuminated by an LED from above. We alternate the colors with green and white leds. These are highly focused using glass lenses that brightly illuminate the ball. The mechanism works perfectly for the green led light but the laser range finder misreads on the balls illuminated on the white light. This made us deduce that it had something to do with the spectrum of light disrupting the laser. This causes the balls to “hiccup” or jump as they reach the upper half of the glass tube. My theory is that the light intensity through the ball, or even bouncing around is disrupting the light from the laser reflecting back to the sensor on the rangefinder.

Now i used to think that i was cool,
drivin' around on fossil fuel,
until i saw what i was doin',
was drivin' down the road to ruin. --JT

Edited by: kennybobby on 02/18/2021 - 00:09
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I would guess that it has something to do with the spectrum of the white LED including 635nm. A green LED won’t disrupt a sensor calibrated to 635nm but even a little light in that frequency from the white LED might disrupt it, especially as the ball gets higher and thus closer to the LED, increasing intensity.
Just a thought…

SammysHP's picture
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It’s a common issue with laser range measurement, for example outdoor with sunlight.