The Series 9 Tiffen Day for Night Monochrome Glass Filter is an effect that makes a scene recorded in daylight appear as if it were taken at twilight.
This is usually accomplished by the use of a filter that both underexposes by about two stops, and can also produce a bluish color overcast. Lighting, contrast, and other factors contribute to the reality of this effect. Day for night filters are a cost-effective alternative to night shooting where overtime charges may apply to cast, crew and rental equipment of lighting gear.
Tiffen's ColorCore glass is produced through a process that entails permanently laminating the filter material in between two pieces of optical glass that are ground flat to tolerances of a ten-thousandth of an inch, then mounting them in precision aluminum rings.