Optically a solar power tower is the same as a circular Fresnel reflector. Parabolic trough and concentrating linear Fresnel reflectors are classified as linear focus collector types. The PIR sensor consists of a pyroelectric sensor and a Fresnel lens. More complicated models of diffraction require working with the mathematics of Fresnel or Fraunhofer diffraction. Each individual facet is a Fresnel lens. That means that a Fresnel diffraction pattern can have a dark center. Similar calculations for the near field can be done using the Fresnel diffraction equation. In the center are amber and red lights composed of Fresnel lenses. This is most commonly achieved through the use of fresnel prisms. The dimensions of the setup must comply with the requirements for Fresnel diffraction. This arrangement is known as a Fresnel lens. This has also recently included Fresnel type lenses. Thus the specification of the Fresnel rhomb was completed. The spiral is closely related to the Fresnel integrals and the Euler spiral. The mirror represents a flat roof within region 1 of the Fresnel zone.