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Twilight occurs according to the solar elevation angle θ s, which is the position of the geometric center of the Sun relative to the horizon. There are three established and widely accepted subcategories of twilight: civil twilight (nearest the horizon), nautical twilight, and astronomical twilight (farthest from the horizon).
During power failures, they'll shine bright white and can be removed from the outlet and used as a portable flashlight. With a long life LED, this night light will outshine the rest.
1 watt 9 volt three chips SMD phosphor based white LED. Among the challenges being faced to improve the efficiency of LED-based white light sources is the development of more efficient phosphors. As of 2010, the most efficient yellow phosphor is still the YAG phosphor, with less than 10% Stokes shift loss.
New street lighting technologies, such as LED or induction lights, emit a white light that provides high levels of scotopic lumens. It is a commonly accepted practice to justify and implement a lower luminance level for roadway lighting based on increased scotopic lumens provided by white light.
The distinction is not absolute, because crepuscular animals may also be active on a bright moonlit night or on a dull day. Some animals casually described as nocturnal are in fact crepuscular. [2] Special classes of crepuscular behaviour include matutinal, or "matinal", animals active only in the dawn, and vespertine, only in the dusk.
For the rest of this comment I am going to assume an LED is a single P-N junction. Regarding reverse voltage: Most if not all LED manufacturers will list an absolute maximum reverse voltage as 5V. Yet, many people are driving LEDs directly from an AC power line (120V or 240V) with a resistor for current limiting.
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