**Fill Light vs. Flash**
LED light boards are commonly referred to as LED fill lights. As the name suggests, their primary function is to "fill in" the lighting rather than act as the main light source. Fill light is used to supplement weak lighting in a scene, especially when the subject’s face is backlit and lacks sufficient illumination. This additional light helps balance the exposure and reduce shadows on the face. In contrast, the main light source is the primary illumination that defines the overall lighting of the scene.
LED fill lights use light-emitting diodes (LEDs) to illuminate the subject. These lights are often found in camera phones or digital camcorders due to their low power consumption and high brightness. However, compared to traditional flashes, LEDs are not as bright. That’s why they’re typically used only for fill light purposes. Some modern smartphones now feature xenon flashes, like the Sony Ericsson K790c, which provide better illumination than standard LED fill lights. Still, unlike LEDs, xenon flashes cannot be used as a flashlight.
Xenon flashes, also known as high-intensity gas discharge flashes, work by using a xenon bulb filled with helium gas. When triggered, the flash circuit rapidly increases the voltage from 12V to over 20,000 volts through a transformer. This high voltage causes the helium gas inside the bulb to ionize and produce a bright, white light with a color temperature ranging between 6,000K and 10,000K—similar to daylight. The light emitted is sharp, clear, and slightly blue or purple in tone.
When the shutter is pressed, the camera sends a signal to the CPU, which then activates the trigger circuit. A transistor turns on, allowing the capacitor to discharge and create a pulse current in the transformer’s primary coil. This current induces a high voltage of nearly 4,000 volts on the secondary coil, which excites the xenon gas inside the flash tube. The stored electrical energy is quickly converted into light during this discharge, resulting in a bright flash.
Early flash lamps had very limited lifespans, with some magnesium-based flashes only working once. According to industry standards, early xenon flashes could last around 10,000 cycles, but in reality, their lifespan was often much shorter. With technological improvements, modern flashes have significantly increased durability and performance.
In contrast, LED flash technology works differently. Instead of relying on gas discharge, LEDs emit light through the movement of electrons across a PN junction. When a voltage is applied, electrons move between energy levels, emitting photons in the process. This makes LEDs more energy-efficient and longer-lasting. High-quality LEDs can last up to 100,000 hours at rated power. However, if a phone uses an LED at a higher current than specified, its lifespan can drop dramatically, sometimes to just hundreds or even thousands of hours.
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