Toshiba LED Application Notes

8/11/2019 Toshiba LED Application Notes

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Toshiba LED

Application Notes

Optical Design Guide for LEDLighting Luminaire

(Optical Design Flow)

WL-1185


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Figure 1 LightEmission from anLED Lamp

Toshiba LED Application Notes (Optical Design Guide for LEDLighting Luminaire )

IntroductionLED lamps are rapidly replacing traditional lighting luminaire. This is being

spurred by a recent rise in energy-saving consciousness and the increasing needs

to reduce environmental burdens. Additionally, it is also being driven by the

advancement of white LED lamps in terms of opto-electrical characteristics, cost

efficiency and reliability. LED lamps greatly differ from traditional lighting luminaire

in size, optical flux, spectrum, temperature characteristics, luminous efficacy, etc.

Therefore, you need to design lighting luminaire in ways suitable for individual LED

lamps used. For best performance, the importance of optical measurement

and simulation is increasing. This application notes discusses optical design for

LED lighting luminaire.

Optical Design for LED Lighting Luminaire

Creating lighting luminaire involves optical design, circuit design, thermal design, mechanical design and

so on. This application notes focuses on optical design for LED lighting applications.

Using an LED lamp as a light source increases design flexibility in terms of color temperature, luminous

flux, etc. However, optical characteristics, package dimensions and other parameters differ from LED to LED;

so you must fully evaluate your optical design. A typical optical design for LED lighting luminaire is shown

below. Different design data is required for each step of the design flow. Each step is explained in the

following subsections.


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1. Deciding Specifications for a Lighting System

The first thing you have to do to start with the designing of a lighting system is to decide its specifications,

which greatly depend on the intended usage environment, rooms or spaces in which it will be used, and the

application. For outdoor lighting, brightness is more important than color temperature or color rendering. For

restaurant lighting, the ability to reproduce food colors, i.e., lighting with high color rendering property, would

be more favored. Spotlights for illuminating specific items should have a narrow view angle, intense beam of

light. So, various factors are involved in the determination of brightness, color temperature, luminous flux,

color rendering, etc. Recently, industry standards for LED lighting luminaire have been established as LED

lighting becomes more popular. Check the latest editions of relevant industry standards before you decidespecifications for a lighting system.

Characteristic Spec

Total luminous flux >2300ml (Neutral White color)

Viewing angle 120(typ)

Color rendering (Ra) >80

Forward current DC 350 mA

Forward voltage 45 V to 95 V

Table 1 L-Shape Socket Tube Type LED Lamp System (for General Lighting)

Source: JEL 801: 2010 standard from the Japan Electric Lamp Manufacturers Association (JELMA)

Figure 2. Optical Design Flow and Required Data


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2. Choosing LED Lamps

Once you have determined your product specifications, the next step is to choose an LED lamp(s) to be

used. Select LED lamps that best suit your needs, referring to luminous flux, chromaticity, radiation pattern

and other characteristics specified in the datasheets from LED vendors. Bear in mind that optical

characteristics vary from LED to LED. This is really important when you use an array of LED lamps in a

lighting system or an array of lighting fixtures in a room or specific space because chromaticity variations of

LED lamps can cause the chromaticity of your lighting luminaire to deviate from a nominal value.

An example of a neutral white LED datasheet (1 W, 5000 K) is shown below, with some annotations.

3. Evaluating LED Lamps

Once you have chosen LED lamps, be sure to evaluate each of them separately. The performance of

lighting luminaire is affected by the heat dissipation performance which varies with the applicationenvironment and conditions, as well as the reflectivity of the materials used. Unless your product

specifications were not met, choose other LED lamps. In some cases, you need to review your product

specifications.

4. Mechanical Design

The next step is mechanical design of your lighting system, taking account of the characteristics of the

chosen LED lamps. Check the materials, characteristics and shapes of the packages, lenses and reflectors

of the LED lamps and create design lighting luminaire that meets your product specifications.

4-1. Number of LED Lamps and Their PlacementDetermine the number of LED lamps and their LED forward current ratings necessary to satisfy the

luminous flux set forth in the product specification. You can reduce the number of LED lamps by using

high-current LED lamps, but doing so might pose thermal challenges or cause the LED display to appear

Determine the LED input current and the number of LEDs

according to the specifications.

This LED offers six luminous flux ranks. Select a rank and

determine the number of LEDs according to your luminous

flux requirement.

Chromaticity is divided into four bins per

ANSI standard. Check the chromaticity

ranges.

Color rendering (Ra) and luminous flux have a

trade-off relationship. Select LEDs with values

that meet your requirements.


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much more glaring. On the other hand, increasing the number of LED lamps results in a cost increase.

Examine the opto-electric characteristics of LED lamps and optimize the number of LED lamps and LED

forward current.

4-2. Lens Design

When using a lens, the first thing you should consider is its material. Glass and plastic lenses are most

commonly used. Glass is not easily scratched and has an excellent transparency. Plastic does not break

easily, and is easy to process, lightweight and inexpensive. Since LED lamps from different manufacturers

have different luminous flux and physical sizes, you need to design lenses that fit your LED specification.

4-3. Reflector Design

You must take the reflectivity and flux distribution into account when designing a reflector. You may also

need to consider the material, physical size, the angle of aperture, etc.

4-4. Glare Reduction

The viewing angle from LED lamps is narrower than that of traditional light sources, causing the luminous

flux per unit area to be higher than traditional lighting luminaire. Thus, designers should be concerned about

glare. To reduce glare, it is effective to optically disperse light by means of a lens or cover.

5. Optical Simulation

To run optical simulation of an LED lighting system, the characteristic data of the LED lamps used in it is

required. If an LED lamp is sufficiently far apart from a lens, etc., it may be regarded as a point light source.

In such cases, a simulation using 3D far-field data will provide results close to measured values. On the

other hand, if an LED lamp is close to a lens, etc., the dimensions and shape of the LED lamp must be taken

into account. In such cases, a 3D far-field model will produce errors between simulated and measured

values. To avoid this, a 3D near-field model should be used instead of 3D far-field model. Figure 3 illustrates

3D far-field and near-field models.

You can use light source modeling software to convert the simulation results obtained using a 3D near-field

model into luminous intensity distribution and ray data. The luminous intensity distribution data consists only

a small amount of data and requires no dedicated measurement system, whereas the ray data contains

information about the shape and dimensions of a light source. To convert the measured data into ray data,

you need to specify conversion parameters (the number of rays, shape, dimensions and location of the light

source, etc).

There are many types of simulators. Table 2 lists the simulators supported by light source modelingsoftware called ProSource. For information about ProSource, contact its distributor.

Distributor: Cybernet Systems, Co. Ltd.

3D Far-Field Model 3D Near-Field Model

No need to take care f or Light Source

Light Source

(Shape &

Dimensions)

Luminous Intensity

Distribution

Figure 3 3D Far-Field and Near-Field Models


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6. 3D Near-Field Measurement

To run an optical simulation using ray data, 3D near-field models

of LED lamps are required. If you have a 3D near-field

measurement system, please try measuring the near-field data with

sample. As a side note, Toshiba uses source imaging goniometers(SIGs) from Radiant ZEMAX, LLC for 3D near-field measurement.

Toshiba provides 3D near-field measurement data if you need it for

LED lamp selection.

For information about source imaging goniometers (SIGs) from

Radiant ZEMAX, contact its distributor.

Distributor: Cybernet Systems, Co. Ltd.

For 3D near-field measurement by Toshiba, a sample on the

gonio-stage is moved over the polar angle range (the angle to the z

axis) of 90 to 180 while the gonio-stage is moved over the

azimuth range (the angle to the x axis on the xy plane) of 0 to360. While doing so, the sample is photographed from arbitrary

points on the hemisphere surface for optical measurement.

Software Format

ASAP Binary

FRED Binary

Generic Binary

Integra ASCII

LightTools Binary

LucidShape Binary

OptiCad Binary

OPTIS/SPEOS Binary

Photopia Binary

SimuLux Binary

Specter ASCII

TracePro Binary

TracePro/OSLO ASCII

Zemax Binary

Luminous Intensity

Distribution DataRay Data

Dedicated

measurement systemN/R Required

Light source

dimensions & s ize N/A Available

Figure 5 Sample Movement

Figure 4 Optical Simulation Flow

Table 2 Simulators Supported by ProSource

ProSource

mentioned herein is atrademark of Radiant ZEMAX, LLC.


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6-1. 3D Near-Field Measurement (Example)

1. Sample: TL1F1-NW0,L, 112 lm (IF = 350 mA typical, Ta = 25C)

The latest version of the TL1F1-NW0,L datasheet is available for download from the Toshiba

Semiconductor & Storage Products Company website.

2. Measurement range: Polar angle = 90to 180, Azimuth = 0to 360

6-2. Measurement Results

ProSource, light source modeling software, allows you to view the true colors, chromaticity and luminous

intensity in the 3D near field from an arbitrary angle. The true color view shows the colors of light as it is

emitted from an LED lamp or luminary. The pseudo-color view of luminous intensity highlights the luminous

intensity distribution in colors. In the following example, the inner wall surface of the package casing is

brightly lit by the LED chip, indicating that it is working as a reflector. The pseudo-color view also allows you

to compare luminous intensities. The luminous intensity view shows the brightness of the LED chip and the

package casing.

Measurement Results (Polar angle: 130, Azimuth: 75)

7. Evaluating a Lighting System

If the optical simulation shows that your design works as it was intended to, assemble hardware prototypes

for evaluation. It is important not only to determine that all product specifications are met but also to evaluate

unit-to-unit variations and product reliability. If everything is fine, then you can proceed with mass production.

Notes

The design flow presented herein is provided merely as an example. It is your responsibility to performdesign verification, check the fitting between simulation and measurement results and determine that the

final design works properly.It is your responsibility to interpret the results of simulation using 3D near-field models.

3D near-field models provided by Toshiba are based on actual measurements. It does not necessarilymean, however, that these models have a sufficient accuracy for your lighting applications. Keep it in mindwhen you request 3D near-field models.

When using Toshiba's LED lamps, please also read the Toshiba LED Application NotesDesign

Considerations.

Conclusion

This application notes discussed optical design for LED lighting luminaire. Optical simulation helps you

design a lighting system quickly and at low costs. However, unless you use data properly, simulation resultsmight differ from actual measurement results. The information in this application notes should be consideredas an example. We hope that you will use it as a guide for optical design.


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