Whenever I see a fluorescent poster board, it appears to be much brighter than it should be. Almost as if it is producing light. So how does that work? Why does the color seem to jump out more than a normal color? Is it just my brain’s interpretation that is causing it to look so bright?
because color and a good deal of straight white light are being reflected, making it glossy/shiny. If only the straight color were reflected, it’d appear ‘flat’. The key is using pinks, lime greens, etc AND getting them to be reflective.
bright = reflective
color = the color(s) being reflected
Fluorescent objects appear brighter than they should be because the pigments in them absorb light from the ultraviolet (invisible) region of the spectrum, and re-emit it in the visible range. Here’s a bit of the history of Day-Glo pigments.
Surfaces coated with fluorescent dyes do in fact emit light, which is what makes them seem so bright.
All dyes absorb light; this is what gives them color. In the most common case, of a dye applied to a substrate, the color you see is a combination of the colors of light that not absorbed by the dye and that are reflected by the substrate.
Most dyes absorb certain colors of light more than others, which causes the light that passes through them (twice, actually) to be colored. A dye that absorbs in the yellow region applied to a white surface will result in a blue appearance because that’s how our eyes interpret white light with blue removed.
In most dyes, the absorbed light is converted to vibrational energy in the dye molecules and is dissipated as heat. Fluorescent dyes, however, reemit the absorbed light energy as light of a lower energy, which is to say, another color. A dye that absorbs blue light and reemits it as green would appear bright yellow-green (yellow from the transmitted light, and green from the fluorescence). Other combinations are possible. Generally blue light is reemitted as green, green as yellow or red, and red as infrared (which is not visible to the eye). Absorbed ultraviolet light (which does not contribute substantially to color, unless you’re a butterfly) can be reemitted as blue. It’s possible to shift further down the spectrum (i.e. ultraviolet reemitted as green), but less common chemically for a variety of complex reasons I will not get into.
It’s also possible to have a fluorescent substrate, but the situation is similiar there and I shall not elaborate.
One of the reasons why fluorescent paints seem so bright is often the emission peak in one region of the spectrum will actually exceed the ambient light level in that spectral region. This makes the object look like it is glowing of its own accord (which, actually, it is).
An extremely geeky article about fluorescence in inks (and the modelling thereof) can be found here.