Abstract

The analysis of the Wien equation shows that a color filter in which the density, δ(δ=log10 transmission) follows the equation δ=(6223/λ)(1/θ1−1/θ2) will reduce both the brightness and the color temperature of a complete radiator at temperature θ1 to that of a complete radiator at a lower temperature θ2. Such a color filter is useful as an absorbing screen in an optical pyrometer. If a color filter has a spectral transmission such that the logarithm of transmittance plotted against 1/λ yields a straight line cutting the 1/λ axis in a point corresponding to approximately λ1=0.40μ, such a filter will serve to increase the color temperature of a source although reducing its brightness. The spectral formula of such a filter is βt=0.4343 C2(1/λ1−1/λ) (1/θ2−1/θ1), θ1 being the color temperature of the light source and θ2 that of the transmitted light expressed in accordance with the Wien equation. With a given filter the reciprocal color temperature is raised by the same amount irrespective of the color temperature of the source and the change in reciprocal color temperature is proportional to the thickness of the glass color filter used. If two points 2 and 3 on the spectrophotometric curve of such a Daylite glass are given, then 1/θ1−1/θ2=αt=0.0001607(β2tβ3t)/(1/λ2−1/λ3). With αt to represent the change in reciprocal temperature for the given glass of thickness t, the change per unit thickness is α. Artificial light sources may be described as having a spectral energy distribution in accordance with Wien’s equation within the limits of the visible spectrum. Various phases of daylight produce a visual sensation equivalent to the energy distribution as given by Planck’s equation or by a suitable but different choice of θ the same distribution may also be represented by Wien’s equation within the narrow limits of the visible spectrum, 0.40μ to 0.70μ. A table is included giving the color temperature of some of the artificial light sources and their reciprocals, also the equivalent temperature with its reciprocal for various phases of daylight expressed both according to the Planck and according to the Wien equation.

© 1933 Optical Society of America

Full Article  |  PDF Article
OSA Recommended Articles
The Selection of Color Temperature Altering Filters

Roger S. Estey
J. Opt. Soc. Am. 26(7) 293-297 (1936)

The Calculation of Filters for Color Temperature Conversion

K. S. Weaver
J. Opt. Soc. Am. 26(9) 339-342 (1936)

Note on the Computation of the Alteration of Color Temperature by Blue Filters

W. E. Knowles Middleton
J. Opt. Soc. Am. 44(6) 499-499 (1954)

References

You do not have subscription access to this journal. Citation lists with outbound citation links are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription

Cited By

You do not have subscription access to this journal. Cited by links are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription

Figures (4)

You do not have subscription access to this journal. Figure files are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription

Tables (3)

You do not have subscription access to this journal. Article tables are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription

Equations (19)

You do not have subscription access to this journal. Equations are available to subscribers only. You may subscribe either as an OSA member, or as an authorized user of your institution.

Contact your librarian or system administrator
or
Login to access OSA Member Subscription