Whereas a spherical lens is perfectly symmetric along a central rotational axis, it is not the case for the cylindrical ones.  Which means while the rotation angle by which the lens is used has no impact for the first one but will impact the optical system for the former one. Assembly of cylindrical lenses are therefore subject to one more constraint.

The primary DHS colors are required for use in key​ design elements (such as headings, features, etc.). Secondary colors should be used sparingly and are meant to supplement the primary colors or draw attention to specific areas of content​.

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Note: the Color Contrast Analyzer (CCA) tool helps you determine the legibility of text and the contrast of visual elements, such as graphical controls and visual indicators. It is available for download both as part of the WAT 2015 and WAT 2012 toolsets and as a standalone application at https://www.dhs.gov/publication/web-accessibility-toolbar.

Cylindrical lenses are less common than spherical lenses, but are still wide spread in many Photonics applications, below you’ll find a complete guide to let you learn more about it:

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To guaranty a good surface aspect, polishing cylindrical lens use specific polishing toolings and polishing pads. See above an example of such a tool, you’ll notice that for cost saving, several cylindrical glass lenses are polish at the same time.

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​The image below has a mix of key and secondary design elements and demonstrates the correct usage of the DHS Color Wheel.

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A cylindrical lens is a lens with at least one optical surface has the shape of a section of a cylinder. While spherical lenses surfaces are defined from a fix center of curvature and a radius, cylinder lens shape are made along a central axis with a fix radius of curvature.

As designed, the DHS seal inherently fails the color contrast requirement for Section 508 Accessibility. Since the design of the seal is mandated by law there is an exemption in place for its use. This exemption has been issued by the DHS Office of Accessible Systems and Technology, and the DHS Assistant Secretary for Public Affairs.

The main difference stands in the way the light rays are deviated through it. Spherical lens tends to focus on a point whereas cylindrical ones focus on a one dimension line.

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Requirement (9 Color Contrast): There must be contrasting color/shades at a minimum ration of 4.5:1 for discerning between background and foreground content.

When using the DHS color palette, it is the designer's responsibility to ensure that materials prepared meet DHS criteria for Section 508 Accessibility compliance, especially in terms of color dependence and color contrast.

NOTE: The primary and secondary ​DHS colors are also included below and indicated with a star. They correspond with a "50" value on the USWDS color wheel.

Cylindrical lenses are mainly used to focus a incident light signal into a one dimension line, below are the most commun applications :

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Requirement (8 Color): Color must not be the only means of conveying information, indicating an action, prompting a response, or indicating status. Information conveyed through color must also be provided in text displayed on the screen or by visual differentiation.

The DHS Color Palette is the only approved color system used for DHS and its components – variation from these colors is strictly prohibited. The consistent use of the DHS color palette helps ensure uniformity and strong brand recognition. These colors have been rigorously tested, in web and print media, for consistent color representation. The DHS Color Palette also aligns with the color system used by the US Web Design System.

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Cylindrical polishing of a lens doesn’t require rotational polishing machines, but specific polishing  equipment working way and forth in one direction.