I just saw two cautions tapes, both with black lettering, but one was yellow tape and the other was red. The red made it hard to read and as I thought about it white letters would be relatively difficult on the yellow background.
The reason I’m so interested in this is they are both equally not black or white. Both are the combination or removal of all other colors (not exactly but that general gist).
It seems on the color spectrum ROYGBIV that the ends of the spectrum, Red and Violet, are similar as far as their perceived closeness to black. While the central are similar to yellow, Orange and green. So imagine it has something to do with wavelength similarities.
Any thoughts would be great
In: Physics
What you perceive as color and brightness, is the reflection of light from the sun off the object at a certain wavelength and the intensity of that reflection.
The sun emits most of its light in the ‘yellow’ range. That means there is more yellow light for you to perceive as ‘brightness’ vs wavelengths like violet where the sun does not emit as much in that range.
Yellow is brighter than red. So yellow is nearer to white than to black and red is nearer to black than white. To be visible to read something gotta be far away light-wise from the other color
The answers previously given don’t tell the full story.
We *perceive* yellow as a colour that is brighter than red. If you have two sources of light giving out the same luminous intensity, one purely light of a red wavelength, and one purely light of a yellow wavelength, you would perceive the yellow light source as brighter, even though a physical measurement of light intensity gives the same number.
This is a function of the way we perceive light and colour. The combination of colour sensitive cone cells in our retinas and the visual processing that takes place in our brain makes us *think* that yellow is brighter than red. It’s partly because the cone cells in our retinas are sensitive to wavelengths centred around red, green, and blue. Red light stimulates only the red cone cells, whereas yellow light stimulates both the red and green cone cells. This is why our brain perceives yellow as brighter than red or green alone. Similarly for cyan light, which stimulates both the green and blue cone cells, and is perceived as brighter than green or blue light alone of the same luminous intensity.
As for visibility and legibility of text of different colours on different backgrounds, this is easier for our brains to process and interpret when the contrast in perceived brightness is higher. Since yellow is perceived as a “bright” colour, dark text works better, providing higher contrast than white text. And conversely, since red is a “darker” colour, it contrasts better with white text than it does with black text.
As with virtually all questions to do with colour, it’s important to understand that the colours we see are not accurate reflections of reality. They are all perceptions created in our brain, based on the imperfect sampling of wavelengths received by our retinas.
For example, a light of pure yellow wavelengths we perceive as “yellow”. However, light that contains no yellow wavelengths whatsoever, but is instead a mixture of red and green wavelengths, stimulates both the red and green cone cells in our eyes in the same proportions as yellow light. So instead of perceiving it as “red+green”, we perceive it as yellow. We literally cannot tell the difference between yellow light, and a mixture of red and green light. (This is how display screens fool us into seeing yellow with just red, green, and blue pixels.)
If you ever wonder anything about colour, always remember the fact that it’s only a perception in our minds, created by our imperfect eyes and our brain wiring – and *not* a physical thing. Two objects that look identically yellow are *not* necessarily emitting/reflecting the same wavelengths of light. They’re just stimulating your cone cells in the same way.
Source: Human visual system and colour science expert.
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