Abstract

A perforated hemispherical reflector made of half of a Pyrex flask has been employed to collect diffusely reflected light from a surface to be measured on a photo-cell or thermopile placed at a focal point of the hemisphere conjugate to the position of the sample, thus providing adequate amounts of energy on the thermopile to permit spectral-reflectance measurements to longer wave-lengths than with usual reflectance spectrophotometers. Relative diffuse spectral-reflectance curves extending to 2.5μ are given for a number of “infra-red reflecting” paints, showing qualitatively the superiority of high index of refraction, large particle size, and low extinction coefficient in producing layers of pigments having high scattering coefficients in the near infra-red.

The use of the hemispherical integrator with a tungsten source and a Wratten 87 filter and with either a thermopile or photo-cell receiver is illustrated by measurements which show that the thermopile-Wratten 87 system, embracing wave-lengths 0.76 to 2.6μ, produced reflectance factors which more nearly approximated integrated reflection factors for sunlight between 0.76 and 2.4μ and more truly indicated the effect of variations in physical characteristics of the reflecting material than did photo-cell measurements embracing wave-lengths 0.76 to 1.2μ.

The use of a caesium oxide cathode, infra-red image tube in making rapid inspections of surfaces in the region of wave-length shorter than 1.2μ is described.

© 1947 Optical Society of America

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References

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  1. A. H. Pfund and S. Silverman, Phys. Rev. 39, 64 (1932).
    [Crossref]
  2. A. H. Pfund, J. Opt. Am. 23, 270 (1933).
    [Crossref]
  3. A. H. Pfund23, 375 (1933).
  4. R. Bowling Barnes and Lyman G. Bonner, Phys. Rev. 49, 732 (1936).
    [Crossref]
  5. R. Bowling Barnes, Phys. Rev. 43, 31 (1933).
    [Crossref]
  6. C. W. Bryant, J. Opt. Soc. Am. 24, 139 (1934).
    [Crossref]
  7. J. A. Sanderson, J. Opt. Soc. Am. 30, 566 (1940).
    [Crossref]
  8. Paschen, Ber. Berl. Akad. d. Wiss. 27 (April, 1899).
  9. T. Royds, Physik. Zeits. 11, 316 (1910).
  10. W. W. Coblentz, Nat. Bur. Stand. Bull. 9, 283 (1913).
    [Crossref]
  11. Smithsonian Physical Tables, eighth revised edition (1934), Table 434.

1940 (1)

1936 (1)

R. Bowling Barnes and Lyman G. Bonner, Phys. Rev. 49, 732 (1936).
[Crossref]

1934 (1)

1933 (2)

R. Bowling Barnes, Phys. Rev. 43, 31 (1933).
[Crossref]

A. H. Pfund, J. Opt. Am. 23, 270 (1933).
[Crossref]

1932 (1)

A. H. Pfund and S. Silverman, Phys. Rev. 39, 64 (1932).
[Crossref]

1913 (1)

W. W. Coblentz, Nat. Bur. Stand. Bull. 9, 283 (1913).
[Crossref]

1910 (1)

T. Royds, Physik. Zeits. 11, 316 (1910).

1899 (1)

Paschen, Ber. Berl. Akad. d. Wiss. 27 (April, 1899).

Barnes, R. Bowling

R. Bowling Barnes and Lyman G. Bonner, Phys. Rev. 49, 732 (1936).
[Crossref]

R. Bowling Barnes, Phys. Rev. 43, 31 (1933).
[Crossref]

Bonner, Lyman G.

R. Bowling Barnes and Lyman G. Bonner, Phys. Rev. 49, 732 (1936).
[Crossref]

Bryant, C. W.

Coblentz, W. W.

W. W. Coblentz, Nat. Bur. Stand. Bull. 9, 283 (1913).
[Crossref]

Paschen,

Paschen, Ber. Berl. Akad. d. Wiss. 27 (April, 1899).

Pfund, A. H.

A. H. Pfund, J. Opt. Am. 23, 270 (1933).
[Crossref]

A. H. Pfund and S. Silverman, Phys. Rev. 39, 64 (1932).
[Crossref]

A. H. Pfund23, 375 (1933).

Royds, T.

T. Royds, Physik. Zeits. 11, 316 (1910).

Sanderson, J. A.

Silverman, S.

A. H. Pfund and S. Silverman, Phys. Rev. 39, 64 (1932).
[Crossref]

Ber. Berl. Akad. d. Wiss. (1)

Paschen, Ber. Berl. Akad. d. Wiss. 27 (April, 1899).

J. Opt. Am. (1)

A. H. Pfund, J. Opt. Am. 23, 270 (1933).
[Crossref]

J. Opt. Soc. Am. (2)

Nat. Bur. Stand. Bull. (1)

W. W. Coblentz, Nat. Bur. Stand. Bull. 9, 283 (1913).
[Crossref]

Phys. Rev. (3)

A. H. Pfund and S. Silverman, Phys. Rev. 39, 64 (1932).
[Crossref]

R. Bowling Barnes and Lyman G. Bonner, Phys. Rev. 49, 732 (1936).
[Crossref]

R. Bowling Barnes, Phys. Rev. 43, 31 (1933).
[Crossref]

Physik. Zeits. (1)

T. Royds, Physik. Zeits. 11, 316 (1910).

Other (2)

A. H. Pfund23, 375 (1933).

Smithsonian Physical Tables, eighth revised edition (1934), Table 434.

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Figures (7)

F. 1
F. 1

Hemispherical integrator.

F. 2
F. 2

Diffuse spectral reflectance of the TiO2 lacquer reference standard relative to magnesium carbonate.

F. 3
F. 3

Spectral reflectance of a pigment containing an organic toner.

F. 4
F. 4

Spectral reflectance of a stibnite pigment.

F. 5
F. 5

Spectral reflectance of fine and coarse particles.

F. 6
F. 6

Spectral reflectance of a stibnite pigment containing carbon black.

F. 7
F. 7

Spectral-intensity distribution curves for photoelectric cell and thermocouple receivers with tungsten source and Wratten 87 filter.

Tables (2)

Tables Icon

Table I Contrast ratios C=(RwRb)/Rw derived from Fig. 5.

Tables Icon

Table II Diffuse reflectance factors for the spectral bands 0.76–1.2μ (caesium oxide cell), 0.76−2.6μ (thermocouple) and integrated for sunlight 0.76−2.4μ.