Color Temperature

The color temperature is a measurement that is used to define the color of a light source. This is also used to indicate the 'whiteness' or 'warmness' of a light source.

Smarterlight LEDs are available in many levels of Kelvin color temperature. The descriptions used in this site for color temperature conform to the following:

|Warm light: |2500-3500 Kelvin: typical incandescent light bulb

|Cool light: |3500-4500 Kelvin: typical retail space 'white' florescent lighting

|Pure light: |4500-5500 Kelvin: used for high color definition

|Noon sunlight: |5500-6000 Kelvin: normal daylight at mid day on a mid-summer day

The following table offers a broader example of the types of color temperature:

|1900 Kelvin |Candle light or sunlight at sunrise or sunset

|27K - 2700 Kelvin |Often used as accent lighting to blend in with fluorescent 2700K applications.

|3K - 3200 Kelvin |Used as a primary light source for retail applications.

|3700 Kelvin |Coated lamps. Used where a "softer" metal halide light source is desired.

|4000 Kelvin: |Used in general lighting; factories: parking lots, warehouses

|5K - 5500 Kelvin |Daylight lamps: horticulture, aquariums, high color definition.

|5600 Kelvin |Nominal sunlight (mid day during mid summer)

|6000 Kelvin |Starts to get a blue tint like some automotive headlights

For the scientists: The color temperature of light is typically measured in degrees Kelvin or just Kelvin. This scale designates the light sources spectral distribution. The Kelvin scale is a temperature that is on the Celsius scale where 0 degrees Kelvin = -273 degrees Celsius. The Kelvin is the light emitted from a black body energy source at that given temperature.

Sylvania Lighting Specs:

From: http://www.sylvaniaautocatalog.com/new_sylvania/glossary.htm

==Glossary of Lighting Terms== As with any technical or scientific discipline, lighting technology has its own special terms and concepts for defining the characteristics of lamps and luminaries and for standardizing the units of measurement. The most important of these are described here.

==Light and radiation== Light is taken to mean the electromagnetic radiation that the human eye perceives as brightness, in other words that part of the spectrum that can be seen. This is the radiation between 360 and 830 nm, a tiny fraction of the known spectrum of electromagnetic radiation.

==The photometric system== The photometric system consists of four basic variables: luminous flux, luminous intensity, illuminance, and luminance.



==Luminous flux Φ ==
Unit of measurement: lumen [lm]
All the radiated power emitted by a light source and perceived by the eye is called luminous flux Φ. The unit of measurement is the lumen (lm). The visible radiated power of a light source is not expressed in watts but in lumens since the sensitivity of the human eye differs according to the particular wavelength. In US practice, total luminous flux is defined by the mean spherical candle power I_n. The unit is the mscp.
The conversion formula is: Φ = I_n * π.

Luminous intensity I is a measure of the luminous flux Φ emitted in solid angle Ω.

==Luminous Intensity I== Unit of measurement: candela [cd]
Generally speaking, a light source emits its luminous flux is different directions (solid angle Ω ; the unity of measurement is the steradian sr) and at different intensities. The visible radiant intensity in a particular direction is called luminous intensity I. The unit of measurement is the candela (cd).



==Illuminance E== Unit of measurement: lux [lx].
Illuminance E indicates the degree to which an area is illuminated. It is the ratio between luminous flux and the area to be illuminated. The unit of measurement is the lux (lx). An illuminance of 1 lx occurs when an luminious flux of 1 lm is evenly distributed over an area of 1 square meter. In practice, however, it is unlikely that the luminous flux will be so evenly distrubuted over the illuminated area that all the points in this area will have the same illuminance value.



==Luminance L==
Unit of measurement: candelas per square meter [cd/m²]
The luminance L of a light source or an illuminated area is a measure of how much the eye is stimulated and therefore of how great an impression of brightness is created in the brain. Let's assume we are looking at an illuminated (or self-luminious) area from a particular direction. The luminous intensity of this area divided by its size apparent to our eyes is its luminance L. It is measure in candelas per square meter (cd/m²).



==Luminous efficacy η==
Unit of measurement: lumens per watt [lm/W].
Luminous efficacy η indicates the efficiency with which the electrical power consumed is converted into light. It is measured in lumens per watt (lm/W). The luminous efficacy of conventional incandescent lamps (such as R5 W) is typically 10 lm/W, that of tungsten-halogen lamps (such as H7) 26 lm/W, and that of gas discharge lamp (such as D2S) 91 lm/W.

==Color Temperature==
Unit of measurement: Kelvin (K)
The color temperature of a light source is defined in comparison with a "black body radiator" and plotted on what is known as the "Planckian curve" as seen in Figure 6. The higher the temperature of this "black body radiator" the greater the blue component in the spectrum and the smaller the red component. An incandescent lamp with a warm white light, for example, has a color temperature of 2700K, whereas a daylight fluorescent lamp has a color temperature of 6000 K.



==Light Color==
The light color of a lamp can be neatly defined in terms of color temperature. There are three main categories here:

Warm White < 3300 K
Cool White 3300 to 5000 K
Daylight > 5000 K


Despite having the same light color, lamps may have very different color rendering properties owing to the spectral composition of their light.

==Color Rendering==
As a rule, artificial light should enable the human eye to perceive colors correctly, as it would in natural daylight. Obviously, this depends to some extent on the location and purpose for which light is required. The criterion here is the color rendering property of a light source. This is expressed as a "general color rendering index" (Ra). The color rendering index is a measure of the correspondence between the color of an object (its "self-luminous color") and its appearance under a reference light source. To determine the Ra values, eight test colors defined in accordance with DIN 6169 are illuminated with the reference light source and the light source under test. The smaller the discrepancy, the better the color rendering property of the lamp being tested. A light source with an Ra value of 100 displays all colors exactly as they appear under the reference light source. The lower the Ra value, the worse the colors are rendered.

==Weibull Data for Lamp Life==
Weibull distribution has become established as the standard method for analyzing the life of technical products. Endurance tests on products without technical faults produce failure curves which represent the proportion of products that fail in the course of use. Because of their special properties, these curves can be normalized for the purposes of comparison. This involves approximating the distributions to a straight line. To show this, a special coordinate system is needed (named after Dr. E. H. Wallodi Weibull, 1887 to 1979). Service life distribution can now be accurately defined by specifying two points on the straight line, without having to refer to a failure curve.
The following failure rates have been defined as standard failure rates. The B₃ life value represents the premature failure rate of lamps. It means that 3% of all the tested lamps failed after this number of hours burned. The Tc life value represents the failure rate of 63.2% of the lamps. B₃ and T_c are of particular interest in industry. Another important point is the B₅₀ value. This indicates the average life of the lamps (50%).



To show this approximation to a straight line, a special graphic matrix is needed. The failure rates are indicated as a percentage plotted against the number of hours burned. The advantage here is that the distribution of the life of, say, a headlight lamp can be uniquely defined by specifying particular failure rates.

Point 1: The B₃ life value means that 3% of the tested lamps failed after this number of hours burned.

Point 2: The B₁₀ life value means that 10% of the tested lamps failed after this number of hours burned.

Point 3: The B₅₀ life value indicates the average life of the lamps. The failure rate is 50%.

Point 4: The T_c life value represents the characteristic failure rate of 63.2% of the lamps.

Rule of thumb:
5% overvoltage -> *Half the life *15% higher luminous flux *8% higher power consumption *3% higher current

5% undervoltage -> *Twice the life *15% lower luminous flux *8% lower power consumption *3% lower current

All life data presented in this document are given as B₅₀ @ 14.0 volts for halogen products and @ bulb rated voltage for all others unless noted.