Essential for LED product development! The importance of optical measurement and our measurement services

Optical measurement is an essential technology for evaluating the performance of LEDs and lighting products. Accurately measuring the physical properties of light, such as brightness and color, provides reliable data for a wide range of applications, including product design, quality control, and certification testing.
However, because dedicated equipment is required for each measurement item, the introduction cost and operational difficulties become issues. This article provides an easy-to-understand explanation of practical points, from the basics of optical measurement to the main measurement items and equipment, concepts of uncertainty, and our measurement services.

Overview and necessity of optical measurement

What is optical measurement?

Optical measurement is a measurement technique for quantitatively evaluating the physical properties of light (intensity, distribution, color, efficiency, etc.). It is particularly important for accurately understanding the performance of lighting fixtures and LEDs, and it is important to measure optical properties according to product specifications. Dedicated measuring equipment must be prepared according to the measurement item. It is also necessary to consider the variability, known as "uncertainty," of the obtained measurements.

Why optical measurement?

Due to variations during manufacturing, LEDs have different characteristics such as chromaticity and brightness. Although the impact is small when using a single LED, in lighting and display products that incorporate many LEDs, individual differences can lead to problems such as discrepancies in appearance and color.
To avoid these problems, it is important to perform optical measurements using specialized equipment and select LEDs with characteristics as similar as possible.

Main measurement items

The required optical measurement items vary depending on the LED or lighting product being measured. The main measurement items are listed in the table below.
Each item is explained in the following columns, so please check them out.

LED/Laser Technology Column: LED Glossary

List of main measurement items

Main measurement items	unit	Overview	Main measurement applications
luminous flux	Lumens [lm]	An index showing the total amount of light emitted from a light source	Lighting fixture brightness evaluation and lamp performance comparison
luminosity	Candela [cd]	An index showing the light intensity in a specific direction of a light source	Light distribution design, performance evaluation of floodlights and headlights
Light distribution characteristics	Graph display	Characteristics that indicate the directional distribution of light	Light distribution control design for lighting fixtures
Chromaticity	Cx, Cy	Coordinate value that quantifies the color of light (position on the CIE chromaticity diagram)	Color quality evaluation, color management for displays and lighting
color temperature	Kelvin [K]	The color of the light source converted into the temperature of blackbody radiation	Designing lighting atmosphere and adjusting white balance for photos and videos
Color rendering index	Average color rendering index [Ra]	An index that indicates the ability of a light source to make an object's color appear natural	Store lighting, medical lighting, applications where color reproduction is important
spectral distribution	W/nm or relative value	Characteristics that indicate the energy distribution for each wavelength of a light source	Color evaluation, spectral characteristics analysis of light sources, plant growth lighting, etc.

Typical measuring equipment

Optical measurement requires a dedicated measuring device for each measurement item. Representative measuring devices and their uses are introduced below.

List of representative optical measuring devices

Measurement method	Main measurement items	Features and benefits	Main uses
integrating sphere	Total luminous flux, chromaticity, spectral distribution, CRI	Diffuses light evenly and measures total luminous flux	Luminous flux evaluation of LED LAMPS and lighting fixtures
photometer	Luminous intensity, chromaticity, spectral distribution, CRI	Measures luminous intensity by receiving only light from the front of the light source	Indicator and display luminosity evaluation
Light distribution measuring instrument	Light distribution characteristics	Ideal for directivity evaluation, light distribution curve can be obtained	Light distribution characteristic evaluation of LEDs and optical modules

Uncertainty in measurement results

Measurement values obtained through optical measurements always contain "uncertainty" (variation). This uncertainty is unavoidable even when using high-performance measuring instruments. Understanding and properly evaluating uncertainty is essential to ensuring the reliability of measurements.

Main uncertainty sources

The main sources of uncertainty are:
Measurements must be handled with these factors in mind.

Calibration error of measuring equipment
Measurement environment (temperature, humidity, ambient light, vibration, etc.)
Variation in measurement procedures and operators
Individual differences and stability of the object being measured
Differences in data processing and analysis methods

International Guidelines

To evaluate uncertainty, it is necessary to quantitatively confirm the reliability of the measurement value. An index called GUM (Guide to the Expression of Uncertainty in Measurement) is widely used internationally.
GUM is an internationally standardized guideline for the evaluation and expression of measurement uncertainty, "ISO/IEC Guide 98-3." Using equipment and methods calibrated in accordance with this guideline ensures the reliability of measurements and tests.

Introduction to our measurement equipment

We have a variety of optical measuring instruments and can handle typical measurement items.
We also have many LED lighting jigs available, so you can measure individual LED data before mounting on the board.
In addition, by using a large integrating sphere inside which the object to be measured can be placed, optical measurements can be performed on LEDs that have already been mounted on a board or are in the finished product state. Each measuring instrument is introduced below.

Integrating sphere: ISP500

Integrating sphere manufactured by Instrument System
With a large diameter of 500 mm, it is possible to place substrates and modules inside for optical measurements.

photometer

Light intensity measurement fixture
The LED is placed in a dedicated SOCKETS and is primarily used to measure a single LED.

Spectrometer: CAS140-CTS

Spectrometer manufactured by Instrument System
Supports a wide range of wavelengths from visible light to infrared light
Spectral processing is performed using both the integrating sphere and the photometer, and each measurement value can be checked using dedicated GUI software on a PC.

X-ray analysis

In addition to optical measurements, we also use our own X-ray analysis equipment to analyze internal LED failures.
Even if the measurement results show that the amount of light is less than expected or that there is an abnormality in the electrical characteristics, the cause can be investigated at the same time.

About our measurement services

We provide optical measurement services using the measuring equipment introduced here.
It can also be used with devices other than those handled by NEXTY Electronics.
Please also take a look at our quality and analysis support page, which introduces a variety of services, including optical measurement.

Introducing NEXTY Electronics' quality and analysis support features

Summary

Optical measurement is an essential technology for accurately evaluating the quality and performance of LEDs and other light sources and lighting products.
Properly managing variations in individual products and in the measurement environment, and obtaining highly reliable data, plays an important role at each stage of design, development, and quality assurance.
As introduced in this column, optical measurements require a great deal of specialized knowledge, including the selection of measurement items and equipment, and uncertainty evaluation. Utilizing our diverse measurement equipment and know-how, we can meet a wide range of needs, both before and after board mounting. If you require optical measurements for the development or evaluation of LED products, please feel free to contact us.