may be covered with a protective coating, such as a copper layer and varnish. Despite the use of aluminum in generic mirrors, aluminum is not always used as the reflective layer for a solar mirror. The use of silver as the reflective layer is claimed to lead to higher efficiency levels, because it is the most reflective metal. This is because of aluminum's reflection factor in the UV region of the spectrum. Locating the aluminum layer on the first surface exposes it to weathering, which reduces the mirror's resistance to corrosion and makes it more susceptible to abrasion. Adding a protective layer to the aluminum would reduce its reflectivity. Interference layer An interference layer may be located on the first surface of the glass substrate. It can be used to tailor the reflectance. It may also be designed for diffuse reflectance of near-ultraviolet radiation, in order to prevent it from passing through the glass substrate. This substantially enhances the overall reflection of near-ultraviolet radiation from the mirror. The interference layer may be made of several materials, depending on the desired refractive index, such as titanium dioxide. Passive mirror cooling applications The use of solar mirrors as a form of passive daytime radiative cooling for solar radiation management has been proposed to address local temperature increases as well as to decrease global warming. Propositions have focused on the usage of solar mirrors both on the Earth's surface and in space. Terrestrial applications Passive mirror cooling systems reduce temperatures by reflecting solar radiation while shielding the base of the mirrors from heat penetration. The effectiveness of such systems may be reduced with the accumulation of dust on mirrors, with maximum dust accumulation reducing mirror effectiveness by 63%. However, mirrors may be "self-cleaned" by rain (reducing the soiling rate to 18.6%) or cleaned by humans. On a local scale, passive mirror cooling systems have been implemented to lower the energy consumption used to cool residential and commercial buildings and thus offset the need for air-conditioning. When passive mirrored surfaces are placed on roofs, they have been shown to reduce electricity consumption and costs for cooling, with one case study reducing costs by 15%. While the use of solar mirrors as a form of solar radiation management on a global scale has been proposed, more data and funding is required. Increasing awareness of passive radiative cooling's potential to lower costs as well as its