Carpentry is another profession learned through apprenticeship. An apprenticeship is a system of training a new generation of practitioners of a trade or profession with on-the-job training and often some accompanying study (classroom work and reading). Apprenticeship also enables practitioners to gain a license to practice in a regulated profession.
A black light is a source of electromagnetic radiation that emits near-ultraviolet light, usually in the 350-375 nanometer wavelength range. This range is just slightly below the 400nm that human eyes can detect. When this light is reflected off certain materials, it looses energy and its wavelength expands to over 400nm. The reflected light is then visible to human eyes, and the illuminated objects appear to glow.
LEDs come in many colors, and some LEDs contain multiple elements and are therefore capable of multiple colors. LEDs are most commonly used for keypad backlights and service/message indicator lights. LEDs are also often used for LCD display backlights. Bright white LEDs can provide a flashlight function. Recently, bright white LEDs have also been used to provide a flash function for a camera-phone. An LED camera flash is generally not as bright as the xenon technology used in standalone cameras. Some LED flashes are brighter than others, however (up to 20 times brighter, in some cases.). LED flashes remain lit for a period of time, unlike the extremely brief strobe of light produced by xenon technology.