I like this topic. The trend in the auto lighting industry seems to be toward higher color temperature lighting (less red/yellowish and more bluish/violet). I have a graduate degree in physiologic optics and vision science, but I'm still not sure I understand the visual implications of the trend toward higher color temperature. There are so many factors that contribute to how the human visual system perceives the world that it’s hard to predict how the different physical properties of the light translate into actual visual perception. There have been many clinical studies, and a few that are ongoing.
It’s interesting to hear what you guys have to say. Here are a few factors I can think of, some of which were already mentioned:
1) Yellow light scatters less than blue light in the atmosphere (or stated another way, shorter wavelength light scatters more). Why is the sky blue? Why does the sun appear yellow? Why do marksmen and hunters prefer yellow tinted lenses? The answer is because blue light scatters in the atmosphere. Remove blue light and there will be less scatter. In a vacuum the rules are different, but that’s another story.
2) Retinal sensitivity to light varies depending on lighting conditions: The scotopic system (dark adapted, using rods) is used in low light situations and is most sensitive to light in the 505 nm range (yellow-greenish light). The photopic system (light adapted, using cones) is used during the day and is most sensitive to light in the 555 nm range (more greenish). The mesoptic system is a combination of the scotopic and photopic. The mesoptic system is used during low light conditions, like at dusk. I’m not sure how these systems comes into play, but I would think this suggests that per lumen, yellow light is more efficient for human vision AT NIGHT. That being said, you don’t see many people preferentially driving around with yellow-green lights.
3) Perceived brightness is different than usable light. Perceived brightness increases as a logarithmic function of reflected light intensity. In other words, the relationship between brightness of a light and how bright we perceive light is not linear. Added to this is that scattered light can be perceived as brightness. Therefore scattered blue light may make us perceive more brightness even if it does not contribute to a usable image. I’ve heard this as a theory of why drivers prefer the high color temperature of HID lighting.
4) Human psychology probably plays a huge role in “preferred” color temperature. There are all kinds of studies out there that look at the affect of different wavelengths of lighting on how humans behave. The results are interesting. How does street light color affect crime rates? What color lights in the class room do students learn more? What color should office lighting be to encourage productivity? What colors in restaurants encourage people to order more food?
Interesting stuff, but yet, I don’t have any real answers. I admit to enjoying my HID lighting over halogen, even though that’s counter intuitive to me. From a physiological optics stand point, I would think yellow would be a better color for fog lights
Anyway, I’m glad to see the discussion.
It’s interesting to hear what you guys have to say. Here are a few factors I can think of, some of which were already mentioned:
1) Yellow light scatters less than blue light in the atmosphere (or stated another way, shorter wavelength light scatters more). Why is the sky blue? Why does the sun appear yellow? Why do marksmen and hunters prefer yellow tinted lenses? The answer is because blue light scatters in the atmosphere. Remove blue light and there will be less scatter. In a vacuum the rules are different, but that’s another story.
2) Retinal sensitivity to light varies depending on lighting conditions: The scotopic system (dark adapted, using rods) is used in low light situations and is most sensitive to light in the 505 nm range (yellow-greenish light). The photopic system (light adapted, using cones) is used during the day and is most sensitive to light in the 555 nm range (more greenish). The mesoptic system is a combination of the scotopic and photopic. The mesoptic system is used during low light conditions, like at dusk. I’m not sure how these systems comes into play, but I would think this suggests that per lumen, yellow light is more efficient for human vision AT NIGHT. That being said, you don’t see many people preferentially driving around with yellow-green lights.
3) Perceived brightness is different than usable light. Perceived brightness increases as a logarithmic function of reflected light intensity. In other words, the relationship between brightness of a light and how bright we perceive light is not linear. Added to this is that scattered light can be perceived as brightness. Therefore scattered blue light may make us perceive more brightness even if it does not contribute to a usable image. I’ve heard this as a theory of why drivers prefer the high color temperature of HID lighting.
4) Human psychology probably plays a huge role in “preferred” color temperature. There are all kinds of studies out there that look at the affect of different wavelengths of lighting on how humans behave. The results are interesting. How does street light color affect crime rates? What color lights in the class room do students learn more? What color should office lighting be to encourage productivity? What colors in restaurants encourage people to order more food?
Interesting stuff, but yet, I don’t have any real answers. I admit to enjoying my HID lighting over halogen, even though that’s counter intuitive to me. From a physiological optics stand point, I would think yellow would be a better color for fog lights
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