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In visual perception, flicker is a human-visible change in luminance of an illuminated surface or light source which can be due to fluctuations of the light source itself, or due to external causes such as due to rapid fluctuations in the voltage of the power supply (power-line flicker) or incompatibility with an external dimmer.
Most modern ballasts are now also equipped with a dimmer, which uses pulse-width modulation to dim the lamp up to 50%, or as much as one stop of light. Unlike a tungsten-based light, which has a negative color temperature shift with a drop in power, the mercury emission spectra takes over with a drop in power (approximately 200 K bluer at 50% ...
Reverse bias: Although the LED is based on a diode junction and is nominally a rectifier, the reverse-breakdown mode for some types can occur at very low voltages and essentially any excess reverse bias can cause immediate degradation, and may lead to vastly accelerated failure. 5 V is a typical maximum reverse bias voltage specification for ...
Temporal light artefacts (TLAs) are undesired effects in the visual perception of a human observer induced by temporal light modulations. Two well-known examples of such unwanted effects are flicker and stroboscopic effect. Flicker is a directly visible light modulation at relatively low frequencies (< 80 Hz) and small intensity modulation levels.
The Lexus LS 600h (XF40) features LED low beam, position and side marker lights in North America, and the 2009 Cadillac Escalade Platinum used LEDs for the low and high beams, as well as for the position and side marker lights. The Mercedes-Benz S-Class (W222) used entirely LED lights, even in the most basic trim level.
LED power dissipation is modeled as a current source; thermal resistance is modeled as a resistor; and the ambient temperature is modeled as a voltage source. High power light-emitting diodes (LEDs) can use 350 milliwatts or more in a single LED. Most of the electricity in an LED becomes heat rather than light – about 70% heat and 30% light. [1]
The requirements of a flicker measurement equipment are defined in the international electro-technical standard IEC 61000-4-15. [2]A flickermeter is composed of several function blocks which simulate a 230 V/60 W or a 120 V/60 W incandescent lamp (reference lamp) and the human perception system (eye-brain model).
The circuit must provide sufficient current to light the LED at the required brightness, but must limit the current to prevent damaging the LED. The voltage drop across a lit LED is approximately constant over a wide range of operating current; therefore, a small increase in applied voltage greatly increases the current.