In a lighting installation composed of a sufficient number of lamps for statistical evaluation, the total luminous flux of the lamps loses approximately 30% due to lamps becoming unusable and reduction of luminous flux after 100 hours of usage.
Driver efficiency depends on the load ratio.
Average Life
In a lighting installation composed of a sufficient number of lamps for statistical evaluation, the time it takes for 50% of the lamps to become unusable under normal conditions. The average life of LED chips depends on the junction temperature. LEDs driven at high currents have higher temperatures and shorter life. LM 80-08 "Approved Method: Measuring Lumen Maintenance of LED Light Sources" defines the decay of luminous flux over time and requires LED manufacturers to provide measurements for at least 6000 hours of luminous flux. Measurements should ideally be taken every 1000 hours up to 10000 hours. For periods longer than 10000 hours, TM 21-11 "Approved Method: Measuring Lumen Maintenance of LED Light Sources" is used. Measurements are extrapolated to estimate long-term performance. The time until luminous flux decreases to 70%, i.e., economic life, is predicted. Example life estimates for an LED chip driven at different current levels are given below.
Color Temperature
The color temperature of a "black body" that has the same spectrum as the light source being evaluated. Unit is Kelvin (K). A black body absorbs all radiation at different wavelengths. When heated, it emits light from yellowish to white to bluish-white. The color of light sources depends on the spectral intensity differences. The temperature at which a "colored temperature object" emits light like a black body is the color temperature.
Color Rendering Index (Ra)
The ability of light sources to reveal colors of illuminated objects is measured by the Color Rendering Index (CRI). CRI allows comparison of different light sources. Continuous daylight spectrum is used as a reference. CRI is shown as Ra, unitless, ranging from 0 to 100. Ra=100 means the light source spectrum matches the reference source.
Luminaires
Luminaires are used to control the distribution of light from light sources, give desired shapes, protect lamps and electrical circuits from physical effects, limit glare, and provide aesthetic and comfort needs. Photometric data of luminaires are essential for lighting calculations. This includes light distribution surfaces or curves, luminaire efficiency, glare, and more.
Light Distribution Surface and Curves
The geometrical locus of the endpoints of light intensities in various directions is called the light distribution surface. Measurements are taken along infinite directions. Practically, light distribution curves or intensity tables are provided for sections. Light distribution curves and intensity tables are reduced to 1000 lm (cd/klm). According to CIE, distribution curves A, B, and C are provided for three different planes.