Abstract

A description is given of the apparatus and method used to measure the spectral characteristics of daylight between 285 and 775 mμ. These measurements, extending over approximately seven months, were made at Pretoria on total daylight, skylight without sun, and south sky. Spectral energy distributions, CIE chromaticity coordinates, correlated color temperatures, and illuminance values were calculated. The total of 422 sets of spectral energy distributions were averaged into a number of different groups. The derived chromaticities were found to be much closer to the full radiator locus than those previously published, which had been obtained in the northern hemisphere. The ultraviolet content also proved to be relatively high.

© 1966 Optical Society of America

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References

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  1. S. J. Richards and S. African, Architectural Rec. 36, 251 (1952); A. Angstrom and A. J. Drummond, Arch. Meterol. Geophys. Bioklimatol., Ser. B 12, 41 (1962).
    [CrossRef]
  2. S. T. Henderson and D. Hodgkiss, Brit. J. Appl. Phys. 14, 125 (1963); Brit. J. Appl. Phys. 15, 947 (1964).
    [CrossRef]
  3. D. B. Judd, D. L. MacAdam, and G. Wyszecki, J. Opt. Soc. Am. 54, 1031 (1964); Y. Nayatani and G. Wyszecki, ibid.53, 625 (1963); H. R. Condit and F. Grum, ibid. 54, 937 (1964).
    [CrossRef]
  4. W. E. K. Middleton and C. L. Sanders, Illum. Eng. (N. Y.) 48, 254 (1953); G. T. Winch, Trans. Illum. Eng. Soc. (London) 21, 91 (1956).
  5. K. L. Kelly, J. Opt. Soc. Am. 53, 999 (1963).
    [CrossRef]
  6. G. T. Winch, Trans. Illum. Eng. Soc. (London) 28, 66 (1963).

1964 (1)

1963 (3)

S. T. Henderson and D. Hodgkiss, Brit. J. Appl. Phys. 14, 125 (1963); Brit. J. Appl. Phys. 15, 947 (1964).
[CrossRef]

K. L. Kelly, J. Opt. Soc. Am. 53, 999 (1963).
[CrossRef]

G. T. Winch, Trans. Illum. Eng. Soc. (London) 28, 66 (1963).

1953 (1)

W. E. K. Middleton and C. L. Sanders, Illum. Eng. (N. Y.) 48, 254 (1953); G. T. Winch, Trans. Illum. Eng. Soc. (London) 21, 91 (1956).

1952 (1)

S. J. Richards and S. African, Architectural Rec. 36, 251 (1952); A. Angstrom and A. J. Drummond, Arch. Meterol. Geophys. Bioklimatol., Ser. B 12, 41 (1962).
[CrossRef]

African, S.

S. J. Richards and S. African, Architectural Rec. 36, 251 (1952); A. Angstrom and A. J. Drummond, Arch. Meterol. Geophys. Bioklimatol., Ser. B 12, 41 (1962).
[CrossRef]

Henderson, S. T.

S. T. Henderson and D. Hodgkiss, Brit. J. Appl. Phys. 14, 125 (1963); Brit. J. Appl. Phys. 15, 947 (1964).
[CrossRef]

Hodgkiss, D.

S. T. Henderson and D. Hodgkiss, Brit. J. Appl. Phys. 14, 125 (1963); Brit. J. Appl. Phys. 15, 947 (1964).
[CrossRef]

Judd, D. B.

Kelly, K. L.

MacAdam, D. L.

Middleton, W. E. K.

W. E. K. Middleton and C. L. Sanders, Illum. Eng. (N. Y.) 48, 254 (1953); G. T. Winch, Trans. Illum. Eng. Soc. (London) 21, 91 (1956).

Richards, S. J.

S. J. Richards and S. African, Architectural Rec. 36, 251 (1952); A. Angstrom and A. J. Drummond, Arch. Meterol. Geophys. Bioklimatol., Ser. B 12, 41 (1962).
[CrossRef]

Sanders, C. L.

W. E. K. Middleton and C. L. Sanders, Illum. Eng. (N. Y.) 48, 254 (1953); G. T. Winch, Trans. Illum. Eng. Soc. (London) 21, 91 (1956).

Winch, G. T.

G. T. Winch, Trans. Illum. Eng. Soc. (London) 28, 66 (1963).

Wyszecki, G.

Architectural Rec. (1)

S. J. Richards and S. African, Architectural Rec. 36, 251 (1952); A. Angstrom and A. J. Drummond, Arch. Meterol. Geophys. Bioklimatol., Ser. B 12, 41 (1962).
[CrossRef]

Brit. J. Appl. Phys. (1)

S. T. Henderson and D. Hodgkiss, Brit. J. Appl. Phys. 14, 125 (1963); Brit. J. Appl. Phys. 15, 947 (1964).
[CrossRef]

Illum. Eng. (N. Y.) (1)

W. E. K. Middleton and C. L. Sanders, Illum. Eng. (N. Y.) 48, 254 (1953); G. T. Winch, Trans. Illum. Eng. Soc. (London) 21, 91 (1956).

J. Opt. Soc. Am. (2)

Trans. Illum. Eng. Soc. (London) (1)

G. T. Winch, Trans. Illum. Eng. Soc. (London) 28, 66 (1963).

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Figures (12)

Fig. 1
Fig. 1

Schematic layout of apparatus for spectroradiometric measurement of daylight. A=Reference and/or radiometric standard lamp. B=Potentiometer. C=25-cm-diam integrating sphere. D=Carl Leiss quartz-prism double monochromator. E=Wavelength drum of monochromator. F=3 to 1 reduction gear. G=Studded disks for operating microswitches for command. H=Microswitches for command signals. I=Command-signal amplifier. J=Headphones. K=Wormgear reduction and hand drive. L=Alternative motor drive. M=Photomultiplier. N=Mains-operated H. T. precision voltage supply. O=Resistance across which H. T. voltage is measured. P=Digitial voltmeter. S=Position of detachable screen for restricting view to south sky.

Fig. 2
Fig. 2

Open assembly of spectroradiometric apparatus.

Fig. 3
Fig. 3

Integrating sphere with radiation screen.

Fig. 4
Fig. 4

Photometric screen for south-sky measurements, with thermally shielded apparatus.

Fig. 5
Fig. 5

CIE chromaticities of individual measurements of daylight in relation to the locus of chromaticities of a full radiator. Open circles: total daylight with sun. Dots: total daylight without sun. Crosses: south sky.

Fig. 6
Fig. 6

Average spectral distribution curves of daylight derived from four 25-mired-internal groups selected from 422 individual sets with correlated color temperatures ranging from 5000°K to 13 000°K.

Fig. 7
Fig. 7

Average CIE chromaticities of daylight in the northern hemisphere (Henderson, Judd et al.) and the southern hemisphere (present work) based on averages of 2% selection and 10-mired-interval groupings. A: full-radiator locus. B: N.P.R.L., Pretoria. C: Henderson, 1964. D: Judd, MacAdam, Wyszecki, 1965.

Fig. 8
Fig. 8

Ratio of the energy between 300 and 400 mμ to the energy between 300 and 775 mμ. Top curve: full radiators.

Fig. 9
Fig. 9

A: Relation between average derived illuminance and cloud cover for south sky. B. Relation between average derived illuminance and cloud cover for total sky without sun. C: Relation between average correlated color temperature and cloud cover for south sky. D: Relation between average correlated color temperature and cloud cover for total sky without sun.

Fig. 10
Fig. 10

Histogram showing frequency of occurrence of daylight of the three classes separately. A: Total daylight including sun. B: Total skylight without sun. C: South sky.

Fig. 11
Fig. 11

Histogram showing frequency of occurrence of all classes of daylight (combination of A, B, and C in Fig. 10).

Fig. 12
Fig. 12

Diagram showing 5940°K full-radiator curve and 5940°K curve obtained by removing absorption dip at 430 mμ from average 5800°K daylight curve.

Tables (2)

Tables Icon

Table I Average relative spectral irradiance for 25-mired-interval grouping (E1 to E4) and 10-mired-interval grouping (E5 to E13) of 422 sets of daylight measurements ranging from 90 mireds to 190 mireds (see Fig. 6).

Tables Icon

Table II Derived relative spectral energies of daylight at correlated color temperatures 5500°K, 6500°K, and 7500°K