critical wavelength

critical wavelength

[′krid·ə·kəl ′wāv‚leŋkth]
(communications)
The free-space wavelength corresponding to the critical frequency.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
In its proposed rule, the FDA introduces UVA I/UV ratio calculation in addition to the critical wavelength requirement to address broad spectrum protection of a sunscreen product.
Dashed line marks the critical wavelength ([[lambda].sup.*] [approximately equal to] 437 nm) at which the topological transition takes place: the effective medium transforms from common elliptical to hyperbolic state.
It can be determined that the critical wavelength is about 0.8 m.
For UVA, Consumer Reports con ducted a critical wavelength test similar to what the Food and Drug Administration requires of manufacturers.
There is currently no internationally established standard for testing and measuring UVA protection (20); therefore, three reference indices were used: the critical value of absorption (C[lambda]) determined by the critical wavelength method) (21), the UVA/UVB absorbance ratio (22) and the spectral uniformity index (SUI) (23).
We plot the R and T in the wavelength domain (from 100-1200 nm) from which a 50/50 BS can be obtained at a critical wavelength [[lambda].sub.c] which is indicated by the vertical arrow.
The thicknesses of the alternate layers are taken as a = 182 nm and b = 291 nm according to the quarter wave stack condition a = [[lambda].sub.c]/4[n.sub.1] and b = [[lambda].sub.c]/ 4[n.sub.2], while [[lambda].sub.c] = 1750 nm is the critical wavelength which is the mid-wavelength of the wavelength range considered in our numerical computation.
To earn the seal a product must have UVB protection of SPF 15, UVA protection with a critical wavelength score of 370 or a persistent pigment darkening (PPD) score of 5, and proof of photostability.
The bifurcation point is characterized by a critical wavelength of the periodic disturbance.
DeLeo explained that there is no way to know the degree of UVA protection offered by sunscreens marketed in the United States, unlike in Europe, where products are tested for efficacy and photostability according to critical wavelength, an in vitro assessment, and the persistent pigment darkening method.
Since some metals may hold electrons more firmly than others, the critical wavelength must be shorter in some cases than in others.

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