Selecting LEDs for Your Application Based on Wavelength Specifications

Table of Contents

Introduction
Peak and Dominant Wavelength
High-Brightness LEDs
Relationship Between Luminous Intensity and Directional Characteristics

Introduction

Based on the materials they are produced from, LED lights emit a variety of colors and wavelengths. LED lamps manufactured according to public standards, such as LED lamps for automotive stop lamps or specialized traffic signals, commonly use a standardized bulb as the light source. For these kinds of applications it is recommended that the LED lamp should be selected based on the wavelength specifications.

Peak and Dominant Wavelength

There are two wavelength standards - the peak wavelength and the dominant wavelength. The dominant wavelength corresponds to the color actually identified by the human eye. For most applications, when choosing an LED lamp the range of probable wavelengths is wide. The designers have to choose an LED lamp with wavelengths that best suit their requirements.

Recent developments in luminosity have modified the standards for LED wavelength. Earlier the only type of LED lamps available were high-brightness green GaP LEDs and red GaAlAs LEDs. Therefore it was necessary to choose one of the two for outdoor high-brightness indicators.

High-Brightness LEDs

InGaAlP high-brightness LEDs have recently become availaible on the market. In addition to red LEDs and green LEDs, high-brightness yellow and orange LEDs are now available. Today amber LEDs, orange LEDs, and yellow LEDs are extensively used in the displays of low-current portable equipment that need a high-brightness features and highway LED panels.

Relationship Between Luminous Intensity and Directional Characteristics

Candela (cd) is the unit of measurement for luminous intensity, and Watts/steradian (W/sr) is the unit of measurement for radiance (Figure 1). One steradian can be defined as the solid angle at the center of a one-meter-radius sphere subtended by a square meter of surface area. The steradian is a metric unit.

Figure 1. The relationship between emission wavelength and luminosity for modern LED lamps.

The radiance of light is the quantity of luminous flux propagated in a given solid angle, or the quantity of incident. Therefore, as Figure 2 illustrates, the luminous intensity of an LED lamp is higher when the directionality is narrower. Also for an LED lamp of specified directionality, the higher the emission efficiency of the chip, the higher the luminous intensity.

Figure 2. Relationship between emission wavelength and luminosity for modern LED lamps.

The application and the corresponding viewing angle are listed in the following table:

Applications Viewing angle
High-brightness LED information panel 15° to 30°
Signal applications 8° to 30°
Narrow-direction indicator 30° to 60°
Low-brightness LED information panel 30° to 120°
Wide-direction indicator 60° to 120°
Automotive dashboard wide directionality 60° to 120°
Automotive stop lamp 20° to 50°
Automotive dashboard narrow directionality 20° to 60°

 

Based on the directional characteristics, it is possible to use the same LED chip in the products of various LED manufacturers, to obtain a lamp with varied directional characteristics.

This information has been sourced, reviewed and adapted from materials provided by Marktech Optoelectronics.

For more information on this source, please visit Marktech Optoelectronics.

Ask A Question

Do you have a question you'd like to ask regarding this article?

Leave your feedback
Submit