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Red is red. Blue is blue. Green is green.
At least, that’s how it seems at first glance. Our eyes give us a certain impression of color—and we naturally assume that if two colors look similar, there is similar light.
But from a physical standpoint, that is just not the case.
Two filters may look like an almost identically red to us, yet allow completely different ranges of visible light to pass through. What we perceive as color is the result of complex processing by our visual system. Behind this, however, lies a spectrum: a very specific distribution of different wavelengths.
It is precisely this difference that is crucial when we are interested not only in how a color looks, but also in what light actually reaches the eye.
Visible light spans a broad wavelength range from approximately 380 to 780 nanometers. Within this range, the various photoreceptors in our eyes respond differently to the incoming light. This interaction ultimately gives rise to our perception of color.
This leads to an interesting phenomenon:
Different spectral compositions can produce a very similar color impression.
For example, a red filter can significantly reduce certain green wavelengths while allowing other spectral regions to pass through largely unimpeded. Another filter may also appear red, but it alters the light in a much broader-band manner and is less selective.
To our eyes, both may appear “red” at first glance.
From a spectral perspective, they are not. The color impression alone does not describe the spectral function of a color.
To understand what a color filter actually does to the incoming light, it is therefore not enough to simply look at the filter’s color.
To do this, the spectral transmittance is measured.
A transmission curve shows, for each wavelength, what proportion of the incoming light passes through the filter. This reveals whether a filter almost completely blocks certain spectral regions, partially reduces them, or allows a particularly high amount of light to pass through.
It’s this measurement that reveals a filter’s true spectral “fingerprint.”
The differences can be particularly significant when it comes to color filters.
Another key factor is a color’s saturation.
Although a deep, highly saturated red and a pale red belong to the same color family as we perceive them, there can be a significant difference between the two in terms of their spectral characteristics.
The more white light or other wavelength components a color contains, the less selective the resulting spectrum is.
To put it simply, you can think of it as a dilution: A highly saturated color has a much more pronounced spectral characteristic. As it is increasingly overlaid with broadband light, the basic color impression may remain the same—but the spectral composition changes.
That is why color saturation is not just a matter of aesthetics.
It is a physically significant property of light that enters the eye through a color filter.
Color appearance is not color function.
The SpektroChrom system, developed by Dinshah P. Ghadiali, uses twelve precisely defined, highly saturated colors.
What matters here is not simply that a pair of glasses appears yellow, green, blue, or turquoise, for example. What matters is the specific spectral characteristics of the filter.
The PRiSMA SpektroChrom glasses were therefore not designed with the goal to provide the most pleasant or fashionable color experience. The filters are intended to reproduce the characteristic colors of the SpektroChrom system as accurately as possible.
That is what distinguishes a specific SpektroChrom filter from any ordinary pair of colored glasses.
Therefore, standard red glasses are not automatically SpectroChrom red. Similarly, no blue, green, or violet filter automatically corresponds to the relevant SpectroChrom color.
The visible color is just the first impression.
The range of frequencies is crucial.
Our perception of color is an amazing feat. It reduces complex spectral information to an immediately understandable impression of color.
This is extremely practical for everyday use.
However, anyone who takes a closer look at light and color must go one step further. This is because a color impression does not clearly reveal the wavelengths that make up the light.
This doesn’t just apply to SpektroChrom. We see the same principle at work in sunglasses, blue light filters, artificial lighting, and modern LED light sources.
Two light sources can both appear “white” yet have completely different spectra. Two pairs of eyeglass lenses can look similarly red yet filter out very different wavelengths.
That’s why at PRiSMA Licht, we don’t just look at how it looks, but also at what it’s made of.
When we put on red glasses, the first impression we get is red.
What our eyes actually perceive, however, is not an abstract color name, but light with a very specific spectral composition.
And that is precisely one of the keys to understanding color filters:
The same color family does not mean the same spectrum.
Or even simpler:
We see red—but our eyes perceive a spectrum.
Cover image:
– Composite image based on “Red Theater Curtain” by TrueCreatives via Canva.com and “Prism Reflections” by Evie Shaffer / Pexels via Canva.com
In this article:
– Original images (c) Innovative Eyewear
– AI-generated content
– Collage based on “Laptop Mock Up at Workplace in Office” by SeventyFour/Getty Images via Canva.com
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