Light-emitting diodes (LEDs) are based on inorganic (non-carbor based) marterials. An LED is a semi-conducting device that produces light when an electrical current flows through it LEDs were first deceloped in the 1960s but were used only in indicator applications until recently.

Luminous efficacy is the most commonly used measure of the energy efficiency of a light soure, it is stated in lumens per watt (lm/W), indicating the amount of light a light sounrce produces of each watt ofelectricity consumed For white high-brightness LEDs luninous efficacy published by LED manufacturers typically refers to the LED chip only, and does not include driver losses. 

Correlated color temperature (CCT) is the measure used to describe the relatice color appearance of white light sounre. CCT inducates whether a light source appears more yellow/gold orange of more bule, terns of the range of available shades of “white”. CCT is given in kelvins (umit of absoluet temperature).

Color rendering index (CRI) indicates how well a light source renders color of people and objects, compared to a reference sounce, Phosphor conversion is a method used to generate white light with LEDs A blue or near-ultra violed LED is coated with a yellow or multichromatoc phosphor, resulting in white light Lumen depreciation-the decrease in lumen output that occurs as a lamp is operated.

Rated lamp life- The life value assigned to a particular type lamp. This is commonly a statistically determined estimate of average of median o[erational life For certain lamp types other criteria than failure to light can be used; for example, the life can be based on hte average time umtil the lamp type peoduces a given fraction of initial luminous flux.

Conduction- Transfer of heat through matter by communication of kinetic energy from particle to partiocle, An example is the use of a conductive metal shch as copper to transfer heat.

Convection - Heat transfer through the circulatory motion in a fluid (liquid or gas) at a non-uniform temperature. Liquid or gas surrounding a heat sourec provides cooling by convection such as air flow over a car radiator.

Radiation- Energy transmitted through electromagnetic waves. Examples are the heat rediated by the sun and by incandescent lamps.

Junction temperature (Tj) -Temperature within the LED device. Direct measurement of Tj is impractical but can be calcuated based on a known case or board temperature and the materials of thermal  resisiance.