Lightness and Brightness and Other Confusions

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etween about 380 and 780 nm, which is the span that can activate the receptors in the human eyes and trigger a neural process resulting in vision. Physical textbooks and scientists do not, however, fully agree on what wavelength span to include in the concept of light, and sometimes a distinction is made between visible light (380–780 nm) and invisible light. ‘Invisible light’ refers in this case to ultraviolet radiation with shorter and infrared with longer wavelengths than those within the ‘visible spectrum’. Shorter still (gamma- and X-rays) or longer (radio waves) wavelengths are seldom or never referred to as light, but are still included in what is called the electromagnetic spectrum, where the word spectrum originally referred to a visible range of colours. 58 Even if measurements of energy are limited to what is called visible light there is, however, no direct correspondence between the amount of energy and the perceived intensity of light. Examples of physical concepts related to light Speed of light, light-year, wavelength, light energy, electromagnetic spectrum, absorption, radiation, emission, transmission, dispersion, refraction, diffraction, polarisation, interference, photon Examples of physical concepts related to colour Monochromatic, spectral power distribution curve Physical aspects of ‘colour’ Radiation with wavelengths in the span referred to as visible light can be isolated into discrete wavelengths by for example a prism. Then they cause the perception of different hues, as in the rainbow where radiation from the sun is refracted and reflected by water drops acting as prisms. This has led to the convention of presenting the different wavelengths in the form of a spectrum, made up of hues from blue (short wavelength) to red (long wavelength). Radiation within a very narrow band in this spectrum is called monochromatic. There is, however, no absolute relationship between wavelengths and perceived hues 59 – a reason why modern physics often abandons the traditional colour references for wavelengths in favour of terms such as short, middle and long wavelength. http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html. Wavelength information is discarded very early in the visual process. The perceived hue depends on local contrasts and the total viewing situation and also the intensity of the radiation. 54
Monochromatic radiation appears only in very special situations. Normally, the radiation reflected or emitted from an object consists of many wavelengths in different proportions. This can be illustrated as the spectral distribution curve, which is detected by the already mentioned spectroradiometer. Sometimes this curve is understood as a specification of the colour of the object, a definition of colour corresponding with or comparable to the physical notion of light. There is, however, no direct relationship between the physically measurable radiation distribution and the perceived colour. A B 400 500 600 700 nm 400 500 600 700 nm C D 400 500 600 700 nm 400 500 600 700 nm Figure 11: Spectral distribution curves for some light sources. A) Incandescent, B) Low pressure sodium, C) Metal halide, D) LED 55
Page 5: Contents Foreword .................
Page 8 and 9: faculties. It is therefore most fit
Page 10 and 11: We are left with the paint chip. He
Page 12 and 13: The domain of colour psychophysics
Page 14 and 15: greater than the smallest colour di
Page 16 and 17: involved. It is worth mentioning th
Page 18 and 19: Ulf Klarén Natural Experiences and
Page 20 and 21: that without “benefit of logic”
Page 22 and 23: er of mental categories perceptions
Page 24 and 25: ence derives its origin from multip
Page 26 and 27: oth for perception of lightness (Gi
Page 28 and 29: knowledge constitutes logical knowl
Page 30 and 31: INDIRECT EXPERIENCE culturally tran
Page 32 and 33: tinctions and colour similarities.
Page 34 and 35: References Baumgarten, Gottlieb (19
Page 36 and 37: Harald Arnkil Seeing and Perceiving
Page 38 and 39: ception is entirely integrated with
Page 40 and 41: parallel lines although they almost
Page 42 and 43: What Gregory is saying is that at t
Page 44 and 45: Zeki goes on to say to say that Mon
Page 46 and 47: References Billger, Monica (1999).
Page 48 and 49: Light and colour as experienced thr
Page 50 and 51: conventional concepts, which can be
Page 52 and 53: could be called the constancy colou
Page 54 and 55: colours yellow, red, blue and green
Page 58 and 59: Cadmium Red 1.0 0.8 0.6 0.4 0.2 0 4
Page 60 and 61: meaning of the word to be more corr
Page 62 and 63: Examples of photometric concepts an
Page 64 and 65: Examples of colorimetric concepts a
Page 66 and 67: Figure 15. Visual measuring of nomi
Page 68 and 69: References Billger, M. (1999). Colo
Page 70 and 71: Especially problematic is the situa
Page 72 and 73: continually confused with each othe
Page 74 and 75: W 05 10 20 30 40 50 C 60 90 70 80 7
Page 76 and 77: elation to the light source or obse
Page 78 and 79: ecause the lower reflectance of p i
Page 80 and 81: and religious symbolism. It is also
Page 82 and 83: Munsell’s principal hues and Heri
Page 84 and 85: As the inks developed the three-pri
Page 86 and 87: David Hubel has proposed that the f
Page 88 and 89: any hue is one of constant value. I
Page 90 and 91: saturation, taken together, and is
Page 92 and 93: Discussion From all of this one may
Page 94 and 95: The real colours of objects To see
Page 96 and 97: measured either trichromatically wi
Page 98 and 99: Inherent, identity and nominal colo
Page 100 and 101: uniformly coloured. Colour variatio
Page 102 and 103: flexibility is a natural part of th
Page 104 and 105: About the Authors Harald Arnkil is
Page 106 and 107:
Hardin wrote the book for philosoph
Page 108 and 109:
- system 9-10, 13, 22, 29, 49, 51-
Page 110 and 111:
- colour 8, 24-25, 30, 42, 49-50, 5
Page 112:
110
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Lightness and Brightness and Other Confusions

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