Color characteristics of leds

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COLOR CHARACTERISTICS OF LEDS  12TH MARCH 2018 DENNIS  LEAVE A COMMENT

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There’s an array of different LEDs that are available in the lighting market today. The diverse LED characteristics comprise of light color or radiation wavelength and light intensity among other features.

These color characteristics are as a result of an assortment of factors during the manufacturing process. Factors such as semiconductor make-up, fabrication technology used, and encapsulation are also important in determining the LED color appearances.

Understanding LED colors Color is a fundamental feature of light emitting diodes (LEDs).

Initially, there were a limited number of colors available for these xtures. You could only nd red LEDs. However, as technology advanced, there have been signi cant improvements in LED materials and colors.

Color Characteristics of LEDs: Color Temperature One important aspect of color appearance is color temperature, which exempli es how cool/bluish or how warm/yellowish technically white light appears. CCT Correlated Color Temperature (abbreviated as CCT), is actually a metric correlating the source of

light appearance to a pre-heated theoretic dark/black body appearance. As a black-hued body gets hotter, it becomes red, orange, white, and ultimately blue. The CCT value of a light source, provided in Kelvin (K), represents the temperature at which a hot black body closely matches the light source color under investigation. It symbolizes the color of emitted light and not that of illuminated objects.

What is Color Rendering Index (CRI)?

Metrics Color representation has numerous distinct forms, including reference based systems, gamut based systems, and systems which are built upon sophisticated color appearance models.

CRI refers to a measure of delity (that’s how ‘true’ a certain light source is when related to a reference source), but it doesn’t address the issue of color appeal and discrimination.

Chromaticity and LED Colors

Chromaticity refers to an objective interpretation of the quality of color irrespective of its luminance. It consists of two distinct parameters, often described as colorfulness (s) and hue (h). For a speci ed CCT, a light source with a positive Duv value has a chromaticity which falls above the locus of the blackbody (appearing slightly greenish), while a source featuring a negative Duv value has a chromaticity which falls below the locus the blackbody (appearing slightly pinkish).

The In uence of LED voltage drops

The LED voltage drop often lies between 2 and 4 volts. The actual voltage that occurs across the two terminals is highly dependent on the type of LED/materials used and in uences the color of LED in question.

As expected, the voltage curve of an LED broadly resembles that of a forward diode characteristic. But once the diode is switched on, the voltage becomes relatively at for various forward current levels.

LED Characteristics: The Summary The following table gives a summarized insight concerning LED color characteristics.

Wavelength Range In NM

Color Of the LED

Voltage(V) at 20MA

The Type of Material

Below 400

UV(Ultraviolent)

3.1 to 4.4

AIN, AlGaN, AlGalnP

400 to 450

Violet

2.8 to 4.0

GaP,AlGalnP

450 to 500

Blue

2.5 to 3.7

lnGaN

500 to 570

Green

1.9 to 4.0

GaP, AlGalnP

570 to 590

Yellow

2.1 to 2.2

GaAsP, AlGalnP

590 to 610

Orange or Amber

2.0 to 2.1

GaAsP, AlGalnP

610 to 760

Red

1.6 to 2.0

AlGaAs, GaAsP, AlGalnP

Below 760

Infrared

 Below 1.9

GaAs, AlGaAs

 Besides LED color, the following are other major LED speci cations: Light intensity value( denoted as Iv) Current vs. voltage speci cation Reverse voltage Angle of view LED Speci cations for Operational Life

LED’s light intensity doesn’t diminish with time. What this implies is that LEDs have a speci c operational life. This speci cation helps determine the application of different kinds of LEDs. LED speci cations are determined by the following formulas.

L70% = The time taken for a 70 percent illumination (this is also known as lumen maintenance) L50% = The time taken for a 50 percent illumination (also known as lumen maintenance) Note: According to LED standards, your LEDs shouldn’t exhibit any major shift in chromaticity.

These gures’ rationale is that 70 percent lumen maintenance is equated to a 30 percent light output reduction. This’s an approximate threshold gure required to detect to gradual light output reductions.

CHROMATICITY

COLOR CHARACTERISTICS OF LEDS

COLOR RENDERING INDEX (CRI)?

LED SPECIFICATIONS

LEDS

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