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Journal of the Optical Society of America

Journal of the Optical Society of America

  • Vol. 37, Iss. 7 — Jul. 1, 1947
  • pp: 546–553

The Sensitivity of the Human Eye to Infra-Red Radiation


JOSA, Vol. 37, Issue 7, pp. 546-553 (1947)

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The spectral sensitivity of human vision has been measured in the near infra-red, in two areas of the dark adapted eye: the central fovea (cones) to 1000 mµ, and a peripheral area, in which the responses are primarily caused by rods, to 1050 mµ. In both cases the estimates of spectral sensitivity are based upon determinations of the visual thresholds for radiation passing through a series of infra-red filters. By successive approximation, sensitivity functions were chosen which were consistent with the observed thresholds.

The spectral sensitivity of the fovea determined in this way is consistent with previous measurements of Goodeve on the unfixated eye. At wave-lengths beyond 800 mµ the periphery becomes appreciably more sensitive than the fovea. This tendency increases at longer wave-lengths, so that at the longest wave-lengths studied, the radiation appeared colorless at the threshold and stimulated only rods.

Lengthening the exposure time increases the sensitivity of the peripheral retina relative to the fovea. Our measurements involved exposures of 1 second and fields subtending a visual angle of 1 degree. With shorter exposures or smaller fields the fovea is favored, so that under such circumstances the fovea may become more sensitive than the periphery well into the infra-red.

At 1050 mµ the sensitivity of the peripheral retina is only 3×10-13 times its maximum value at 505 mµ. A computation shows that by 1150 or 1200 mµ radiation should be more readily felt as heat by the skin than seen as light by the eye.

DONALD R. GRIFFIN, RUTH HUBBARD, and GEORGE WALD, "The Sensitivity of the Human Eye to Infra-Red Radiation," J. Opt. Soc. Am. 37, 546-553 (1947)

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  1. A recent paper by N. I. Pinegin (1945) has been received since our work was completed. Visual thresholds were measured at 655, 700, 800, 900, and 950 mµ, using as stimulus the exit slit of a monochromator viewed through a 9× eye-piece. The angular subtense of the test field is not stated. The results agree closely with Goodeve's foveal sensitivity function, and the color of the 950 mµ radiation was reported as "an unsaturated red" at threshold, so that it seems clear that foveal vision was involved.
  2. The terms, spectral luminosity and spectral sensitivity, are used interchangeably to denote the reciprocal of the relative energy at each wave-length needed to produce a constant visual effect. The term luminosity directs attention primarily to the radiation, sensitivity to the properties of the eye.
  3. The total visual transmission or luminous transmission of a filter is given by the expression Tv = ∫RλtλKλdλ/∫RλKλdλ. It would seem obvious, therefore, to define the visual transmission at each wave-length as (RλtλKλ/RλKλ); but this would equal simply the radiant transmission, tλ, which is, of course, the same whether measured by eye or with a thermopile (cf. Committee on Colorimetry, 1944, p. 256). Such a definition of spectral visual transmission would be useless. We have chosen instead the very useful expression for this term indicated above.
  4. As noted above, this is true also of the work of Pinegin (1945).
  5. This foveal sensitivity curve, shown in Fig. 4, is a composite of the original measurements of Hyde and Forsythe (1915), Coblentz and Emerson (1918-19), Gibson and Tyndall (1923), Jainski (1938), Fedorov et al. (1940), and Wald (1945b). Its derivation will be described in detail elsewhere. The large depression and minor inflections in the region 440–520 mµ mark the absorption bands of xanthophyll, the pigment of the human yellow patch (Wald, 1945b).
  6. Thomas Young (1802) stated the basic relation between light and heat radiation very soon after the discovery of the infra-red by Herschel in 1800: "… the affections of heat may perhaps hereafter be rendered more intelligible to us; at present, it seems highly probable that light differs from heat only in the frequency of its undulations or vibrations; those undulations which are within certain limits, with respect to frequency, being capable of affecting the optic nerve, and constituting light; and those which are slower, and probably stronger, constituting heat only; …." The present experiments extend into the curious region in which radiation may be regarded with equal justice as light or as radiant heat.

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