Friday, October 2, 2009

Clipboards, Solar Cells & Fluorescence

Colored solar panels have been covered elsewhere, but reading some of the details gives me a new appreciation for my fluorescent clipboard.

In Professor Reisfeld's paper, she notes that for a transparent plate doped with a fluorescent species that "about 75-80% of the luminescence is trapped by total internal reflection in the plate having a refractive index of about 1.5. Repeated reflections of the fluorescent light carry the radiation to the edges where it emerges in concentrated form".

Now the plastic clipboard is not quite the same thing as fluorescent dye films deposited on both sides of an undoped substrate with photocells lining the edges but certainly the repeated internal reflections are cool nonetheless.

And while my clipboard doesn't have tape on it, the oil on my fingers has a different index of refraction which results in some frustrated internal reflection and glowing fingertips.


  1. hmmm... the luminescence (which is really fluorescence, should be emitted uniformly in all directions. Therefore, any of the fluorescent photons heading in a direction that strikes the plastic/air interface at more than the critical angle will be subject to TIR. I am too lazy to figure out if 75-80% is right.

    What happens if you dip the clipboard in mineral oil?

    Solar cells are about energy. How much of the energy of the incoming light is redirected to the edges? This might be a way to capture the UV component of the incoming light, or you could just have no glass or plastic over the generating cell.

  2. If I dip the clipboard in mineral oil all of my sheets of paper will stick to it and it will be harder to use... kidding aside an interesting question.

    The paper linked to doesn't describe how the 75-80% level for TIR was determined. I also agree shifting UV up to the photocell sensitivity range is probably better for energy effciency.