Abstract

The luminance and luminous intensity characteristics of the leaves of several forest species of eucalypts have been investigated and compared with freshly smoked magnesium oxide. Results indicate that different species of the same genus can have distinctive indicatrices. Inspection of the indicatrices for the leaves showed that, for practical purposes, three types of reflection are recognizable, i.e., diffuse, spread, reflex. It seems important therefore that the research worker should be aware of the type of reflection being measured, since this may influence his conclusions. The cusp in the direction of reflex reflection was found to increase rapidly about the normal (0°) to the leaf’s surface and to attain a maximum at the normal. As the angle of incident light is increased from 0° to 45° or more, the spread reflection component becomes increasingly conspicuous. With normal incidence, the maximum luminous intensity was attained in the direction of reflex reflection, but rapidly decreased toward zero beyond about ±60° to the normal.

© 1971 Optical Society of America

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References

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  1. J. A. Howard, Australian J. Biol. Sci. 19, 757 (1966).
  2. H. A. Keitz, Light Calculations and Measurements (Phillips Technical Library, Eindhoven, Holland, 1955) pp. 1–30, 95–105, 137–221.
  3. H. F. Meacock, F. A. Garforth, R. G. Shrubsall, J. Sci. Instrum. 39, 384 (1962).
    [CrossRef]
  4. J. S. Preston, G. W. Gordon-Smith, Proc. Phys. Soc. B65, 76 (1952).
  5. J. S. Preston, Trans. Opt. Soc. 31, 15 (1929).
    [CrossRef]
  6. J. A. Howard, Aerial Photo-Ecology (Faber & Faber, London, 1970).
  7. J. A. Howard, Nature 224, 1102 (1969).
    [CrossRef]

1969

J. A. Howard, Nature 224, 1102 (1969).
[CrossRef]

1966

J. A. Howard, Australian J. Biol. Sci. 19, 757 (1966).

1962

H. F. Meacock, F. A. Garforth, R. G. Shrubsall, J. Sci. Instrum. 39, 384 (1962).
[CrossRef]

1952

J. S. Preston, G. W. Gordon-Smith, Proc. Phys. Soc. B65, 76 (1952).

1929

J. S. Preston, Trans. Opt. Soc. 31, 15 (1929).
[CrossRef]

Garforth, F. A.

H. F. Meacock, F. A. Garforth, R. G. Shrubsall, J. Sci. Instrum. 39, 384 (1962).
[CrossRef]

Gordon-Smith, G. W.

J. S. Preston, G. W. Gordon-Smith, Proc. Phys. Soc. B65, 76 (1952).

Howard, J. A.

J. A. Howard, Nature 224, 1102 (1969).
[CrossRef]

J. A. Howard, Australian J. Biol. Sci. 19, 757 (1966).

J. A. Howard, Aerial Photo-Ecology (Faber & Faber, London, 1970).

Keitz, H. A.

H. A. Keitz, Light Calculations and Measurements (Phillips Technical Library, Eindhoven, Holland, 1955) pp. 1–30, 95–105, 137–221.

Meacock, H. F.

H. F. Meacock, F. A. Garforth, R. G. Shrubsall, J. Sci. Instrum. 39, 384 (1962).
[CrossRef]

Preston, J. S.

J. S. Preston, G. W. Gordon-Smith, Proc. Phys. Soc. B65, 76 (1952).

J. S. Preston, Trans. Opt. Soc. 31, 15 (1929).
[CrossRef]

Shrubsall, R. G.

H. F. Meacock, F. A. Garforth, R. G. Shrubsall, J. Sci. Instrum. 39, 384 (1962).
[CrossRef]

Australian J. Biol. Sci.

J. A. Howard, Australian J. Biol. Sci. 19, 757 (1966).

J. Sci. Instrum.

H. F. Meacock, F. A. Garforth, R. G. Shrubsall, J. Sci. Instrum. 39, 384 (1962).
[CrossRef]

Nature

J. A. Howard, Nature 224, 1102 (1969).
[CrossRef]

Proc. Phys. Soc.

J. S. Preston, G. W. Gordon-Smith, Proc. Phys. Soc. B65, 76 (1952).

Trans. Opt. Soc.

J. S. Preston, Trans. Opt. Soc. 31, 15 (1929).
[CrossRef]

Other

J. A. Howard, Aerial Photo-Ecology (Faber & Faber, London, 1970).

H. A. Keitz, Light Calculations and Measurements (Phillips Technical Library, Eindhoven, Holland, 1955) pp. 1–30, 95–105, 137–221.

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Figures (9)

Fig. 1
Fig. 1

Schematic drawing of the Pritchard photometer showing the telescopic objective lens (O), the first reflecting mirror (M1), aperture (A) in mirror, second reflecting mirror (M2), and lens of eyepiece (E). The luminous flux passing through the aperture in the first mirror and falling on the photomultiplier is imaged on M2 as a black spot. The subtense angle of the instrument is vaired by changing the aperture in M1.

Fig. 2
Fig. 2

Diagram showing the photometer being used to measure the luminance of a leaf at an observation angle of 45°C. The luminous flux is falling normally on the leaf surface mounted on the plate.

Fig. 3
Fig. 3

Diagram showing the photometer (photomultiplier) being used to measure luminance at narrow angles of observation (i.e., 0° to 5°): (1) magnesium oxide coated surface or leaf mounted on platen, (2) collimating lens to provide parallel rays of light on the sample, (3) front-surfaced semireflecting aluminized mirror, (4) pinhole source aperture, (5) condensing lens for focusing luminous flux from source 6 on the source aperture, (7) Pritchard photometer with built in photomultiplier, (8) baffles, (9) black glass absorbing wedge.

Fig. 4
Fig. 4

Luminance indicatrices of a test plate of (smoked) magnesium oxide for angles of incidence of 0°, 30°, 45°, and 60°.

Fig. 5
Fig. 5

Luminance indicatrices of three eucalypt species: (a) (a) E. goniocalyx. (b) E. obliqua, (c) E. regnans. The incident light was normal to the leaf surface.

Fig. 6
Fig. 6

Luminance indicatrices of E. goniocalyx with angles of incidence of 30° (solid line), 45° (dotted line), and 60° (broken line.)

Fig. 7
Fig. 7

Luminous intensity indicatrices of (smoked) magnesium oxide for angles of incidence of 0° (solid line) and 30° (broken line).

Fig. 8
Fig. 8

Luminous intensity indicatrices of three eucalypt species: (a) E. goniocalyx, (b) E. obliqua, and (c) E. regnans.

Fig. 9
Fig. 9

Luminous intensity indicatrices of E. goniocalyx with angles of incidence of 30° (solid line), 45° (broken line), and 60° (dotted line).

Tables (1)

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Table I Comparison of Luminance Factors for Magnesium Oxidea

Equations (1)

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B i o = L / E i · B 45

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