Cyan in the LCD projector

on Thursday, March 21st, 2019 4:06 | by Anders Eriksson

The LCD projector combines green and blue to form the color cyan. However, while using the spectrophotometer to record this wavelenght it seems to be alternating between green and blue to produce the color. The lights does not seem to be illuminated simultaneously.

This picture is composed of four different channels. One each for green and blue, and two channels for cyan. The cyan color needed to be put into separate channels because they were never illuminated at the same time.

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Category: Lab, Operant learning, operant self-learning

4 responses to “Cyan in the LCD projector”

  1. Hi Anders,

    I’d guess that is because you are using a DLP projector which uses a spinning color wheel to project RGB [1]. Using a non-DLP LCD projector should result in all three color channels being displayed at the same time.

    (and a small clarification for anyone else reading this: the projector does not create cyan light but projects equal amounts of green and blue light – which our eye interprets as cyan).

    Cheers,
    Raphael

    [1] https://www.projectorcentral.com/lcd_dlp_update7.htm?page=Rainbow-Artifacts

    • Welcome Raphael!
      IIRC, our projector doesn’t have a wheel any more: http://www.ti.com/tool/DLPLCR4500EVM#2 but I’m not sure.

      • You are right – unlike standard DLP projectors it doesn’t use a white light bulb and a color wheel but three different RGB LED light sources. Nevertheless, the three colors are shone onto the DLP chip in sequence, as there is only a single chip. Thus, you will never get all three colors displayed at the same time.
        Chapter 4.1 in the manual: “The DLPC350
        takes as input 24-, 27-, or 30-bit
        RGB data at a frame rate of up to 120-Hz.
        This frame rate is composed of three
        colors (red, green, and blue) with each
        color equally divided in the 120-Hz
        frame rate. Thus, a 2.78-ms time slot is allocated to each color.”

        Do the fruit flies care?

        • Anders Eriksson says:

          We have conducted pilot experiments to confirm the apparatus is working and everything seems to be in order. However, we are aiming for to replicate the previous design as closely as possible were we used color filters to get the selected wavelengts. But we might have to rethink it as you say, it does not create a “true” cyan. How much knowledge do you have about this? Would it for example be possible to turn green and blue on at the same time to get cyan, rather than having them switch in between?

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