## Abstract

A résumé is presented of the results obtained in an extensive research into the many ways in which glare affects visibility.

Visibility was studied chiefly by the method of least perceptible contrasts of brightnesses. Results are presented showing the influence of adaptation and of form and size of test-object upon contrast sensitivity.

The results of the investigation show that the least perceptible brightness-difference between an object and its background increases directly with the illumination at the eye from the dazzle-source; varies approximately inversely with the square of the angle which the glare-source makes with the line of vision; and is practically independent of the brightness, size, type, distance, etc. of the dazzle-source.

Considerable study has been given to the variations of the pupil under steady, fluctuating, and glaring lights and of their influence upon vision. Results of the investigations upon irradiation, after-images, blinding-glare and light-shocks are also presented.

© 1926 Optical Society of America

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### Equations (39)

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(1)
$$\text{total brightness}={F}_{1}+{B}_{1}$$
(2)
$$\mathrm{\Delta}{F}_{1}=0.9\frac{{f}_{1}-f}{{f}_{1}}F.$$
(3)
$$\text{contrast sensitivity},S=\frac{{F}_{1}+{B}_{1}}{\mathrm{\Delta}{F}_{1}}$$
(4)
$$\text{Contrast sensitivity},Sm\propto {(d-0.5)}^{0.4}$$
(5)
$$\text{ease of seeing}\propto log(\mathrm{\Delta}F/\mathrm{\Delta}{F}_{T})$$
(6)
$$\mathrm{\Delta}F=\frac{{f}_{1}-f}{{f}_{1}}F$$
(7)
$$E/\mathrm{\Delta}F\hspace{0.17em}\text{is practically constant for a given angle}\hspace{0.17em}D.$$
(8)
$$E/\mathrm{\Delta}F\propto {D}^{2.4}$$
(9)
$$E/\mathrm{\Delta}F=22.5{D}^{2}$$
(10)
$$\text{contrast sensitivity},S=({F}_{1}+{B}_{1})/\mathrm{\Delta}{F}_{1}$$
(11)
$$\text{contrast sensitivity},S=\frac{F+{K}_{1}(E/{D}^{2})}{\mathrm{\Delta}F}$$
(12)
$$\mathrm{\Delta}F=F/S+({K}_{1}/S)(E/{D}^{2})$$
(13)
$${B}_{1}=4.3\frac{{E}_{1}}{{{D}_{1}}^{2}}+4.3\frac{{E}_{2}}{{{D}_{2}}^{2}}\xb7\hspace{0.17em}\xb7=4.3\text{\u2211}\frac{E}{{D}^{2}}=4.3\hspace{0.17em}\frac{10}{\pi}\text{\u2211}\frac{BQ}{{D}^{2}}$$
(15)
$${B}_{1}=4.3\frac{10}{\pi}\mathit{\int}\frac{BdQ}{{D}^{2}}$$
(16)
$$\text{contrast sensitivity}\hspace{0.17em}S=43{(d-.5)}^{.44}$$
(17)
$$E/\mathrm{\Delta}F=21{D}^{2}.$$
(18)
$$\frac{E{P}^{2}cos{D}_{n}}{\mathrm{\Delta}F}=370{D}^{1.8}$$
(19)
$${I}_{s}\propto I{\left(\frac{{M}^{\prime}-M}{M}\right)}^{2}\frac{m{T}^{2}}{{\mathrm{\lambda}}^{4}}(1+{cos}^{2}q)\frac{1}{{r}^{2}}$$
(20)
$$d\varphi \propto {I}_{s}{P}^{2}cos{D}_{n}cos\upsilon dl$$
(21)
$$\mathit{\int}d\varphi =\varphi ={K}_{2}{\left(\frac{{M}^{\prime}-M}{M}\right)}^{2}\frac{m{T}^{2}}{{\mathrm{\lambda}}^{4}}\frac{E{P}^{2}}{j}cot{D}_{n}\left\{cos{D}_{n}+\frac{4}{3}{cos}^{3}{D}_{n}-\frac{2}{3}{cos}^{5}{D}_{n}-\frac{sin2{D}_{n}}{3}(1-{sin}^{3}{D}_{n})\right\}$$
(22)
$$log{T}_{1}=1.26logB-0.31logF-4.49$$
(23)
$$F={\left(\frac{B}{1480}\right)}^{4}$$
(24)
$$log{T}_{2}=1.1logB-0.31logF-3.14$$
(25)
$$logT=1.16logB-0.32logF+0.9log{T}_{0}-0.4log\frac{{f}_{1}-f}{{f}_{1}}-4.84$$
(26)
$${B}_{1}={\left(\frac{B{T}_{0}}{yT}\right)}^{x}$$
(27)
$$S=\frac{F+{\left(\frac{B{T}_{0}}{5000T}\right)}^{4}}{\frac{{f}_{1}-f}{{f}_{1}}F}=45{(d-0.5)}^{0.4}$$
(28)
$$A=10.7log{B}_{2}-2.07logF-37.4\hspace{0.17em}\text{minutes}$$
(29)
$$logB=3.3+0.3logF$$
(30)
$$K=logB+0.25logQ-0.3logF$$
(31)
$$P={K}_{3}{\u220a}^{-.16{(F+C)}^{0.4}}$$
(32)
$$P=7{\u220a}^{-.16{F}^{0.4}}$$
(33)
$$\text{equivalent millilamberts increase per meter\u2010candle}=\frac{1.85}{{(1.122)}^{D}}$$
(34)
$$P=7{\u220a}^{-.16}{\left(F+\frac{1.85}{{(1.122)}^{D}}E\right)}^{0.4}$$
(35)
$$\frac{{P}_{0}-{P}^{\prime}}{{P}_{0}}=0.21+0.025log{F}_{0}+0.205log\left(\frac{{F}^{\prime}-{F}_{0}}{{F}_{0}}\right)$$
(36)
$$\frac{{F}^{\prime}-{F}_{0}}{{F}_{0}}<\frac{0.095}{{{F}_{0}}^{.122}}$$
(37)
$$\frac{{P}^{\prime}}{{P}_{0}}=0.79-0.025log{F}_{0}-0.205log\left(\frac{1.4E}{{F}_{0}{D}^{0.72}}\right)$$
(38)
$$\begin{array}{ll}\frac{{P}_{0}-{P}^{\prime}}{{P}_{0}}\hfill & =0.21+0.025log{F}_{0}+0.205log\left(\frac{1.4E}{{F}_{0}{D}^{0.72}}\right)\hfill \\ \hfill & =0.21-0.18log{\text{F}}_{0}+0.205log\left(\frac{1.4E}{{D}^{0.72}}\right)\hfill \end{array}$$
(39)
$$\begin{array}{lll}\hfill & P\hfill & =6.1+0.5logQ-logE\hfill \\ \text{or}\hfill & \hfill & =5.6-0.5logQ-logB\hfill \end{array}$$