Application Note

Light Emitting Diode

Design Considerations for
Full-color Luminaires Using
Discrete Color LEDs

Table of contents
1. Overview ........................................................................................................................ 2
2. LED Product portfolio for full-color luminaires ................................................ 3
3. Color gamut specifications compared with the color gamut of LEDs ..... 4
4. Additive color mixing vs. subtractive color mixing ......................................... 5
5. Color mixing designs using LEDs (i.e. additive color mixing) ..................... 6
6. General cautions/suggestions for using the LEDs .......................................... 8
7. Summary ........................................................................................................................ 9

The part number NxSx119B-V1, NxSx219B-V1, Nxxx757G, NF2E757H-F1, NCSxE17A in
this document are the part numbers of Nichia’s products, and do not have any relevanceor similarity to other companies' products that may have trademark rights.

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Application Note
1. Overview
In recent years, discrete color LEDs1 have started to be used in various types of lighting fixtures for various
applications from residential luminaires that are easy for anyone to use, and controllable even with apersonal smartphone, to large floodlights designed to decoratively illuminate buildings and landscapes.
Before LEDs, in most cases, colored lights were created with large, white halogen lamps incorporated in afloodlight or a stage lighting luminaire with color filters placed in front of the emitted light, as shown in
Figure 1. Now, full-color luminaires using discrete color LEDs are widely available and they have specificadvantages: the size of the lighting fixtures can be reduced since the LEDs are very small (i.e. a few mm inwidth), and since several different color LEDs are incorporated into a single luminaire, many different
colors2 can be created without color filters and/or other external parts. Other advantages include reducing
the number of the luminaires required for the intended application, energy saving, and better color
reproduction.

Light Emitting Diode

This application note provides information on how to create required colors using discrete color LEDs andcautions/suggestions when designing them into luminaires.

Luminaire(white light)
Color Filter
Color Filter

luminaire withdiscrete color
LEDs

Luminaire(white light)

White light + color filters (conventional way of producing colored
light)

Full-color luminaires using discrete color LEDs3

Figure 1. How to create colors with traditional luminaires vs. luminaires using discrete color LEDs

Note:
1

“Discrete color LEDs” refers to single-color LEDs that emit high purity colors (e.g. red, green, blue, etc.).

2

Using red, green, and blue LEDs, each with 256 brightness levels, over 16 million color combinations can be produced (256 * 256 * 256＝16,777,216).

3

This illustration is only a reference image of a full-color luminaire. How the luminaire operates is different than what is shown here.

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Application Note
2. LED Product portfolio for full-color luminaires
Table 1 shows the color LEDs that are mainly used for general lighting. Colors other than RGB (i.e. red,green, and blue) are also available. For further information, contact a local Nichia sales representative.
Table 1. Nichia’s color LEDs
LED Series（Appearance）

Specifications
Part Number4

119B-V1/219B-V1

NCSC119B-V1

NCSB119B-V1

NCSE119B-V1

NCSG119B-V1

NCSA119B-V1

NVSA119B-V1

NCSR119B-V1

NCSC219B-V1

NCSB219B-V1

NCSE219B-V1

NCSG219B-V1

NCSA219B-V1

NVSA219B-V1

NCSR219B-V1

Outline

3.5×3.5×2.0mm

Dimensions
Rater Power

1.0W

Light Emitting Diode

Consumption
Suitable applications/Advantages

757G

Part Number4/757H

OutlineSince this LED is high power and has high luminance, it is usedmostly for floodlights. It also has high color purity and can create
vivid colors.
NE2B757G

NF2E757GR

NF2E757H-F1

NFSY757G

757G: 3.0×3.0×0.65mm

Dimensions
Rater Power

NE2R757G-P6

757H: 3.0×3.0×0.8mm

0.3W

Consumption
Suitable applications

This LED is more suitable for low luminance applications such as/Advantages

sign boards and indoor lighting including indirect lighting.

Part Number4

E17A

NE2G757G

OutlineDimensions
Rater Power
Consumption
Suitable applications/Advantages

NCSCE17A

NCSBE17A

NCSEE17A

NCSGE17A

NCSGE17ANCSAE17A

NCSRE17A

NCSRE17A

1.7×1.7×0.35mm
1.0W
Since this LED series is very small, the luminaire size can be
reduced. All the LEDs in this series have the same forward voltage(VF), regardless of the color.

Note:
4

Nichia part numbers. The 4th character refers to the color of the light as follows: R: red, G: green, B: blue, C: blue (royal blue), E: bluishgreen, A: amber, Y: yellow.

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Application Note
3. Color gamut specifications compared with the color gamut of LEDs
Figure 2 shows the color gamut ranges of LEDs and the following color gamut specifications for color
televisions, PC monitors, etc.
1. NTSC (National Television System Committee) Specification
A specification established to standardize the composite video signals and broadcasting systems foranalog televisions. The gamut range that can be depicted under this specification is wide. However, atthe time it was established, it was difficult for analog TVs to cover the whole range; most of the analog
TVs at that time listed the color reproducibility as "XX % of the NTSC gamut".
2. sRGB Specification

Light Emitting DiodeAn international specification established by International Electrotechnical Commission (IEC). Manycomputer monitors, printers, and digital devices such as digital cameras follow this specification. Colordifferences may occur when two or more devices are connected; those differences can be reduced
when all the devices connected to each other comply with this specification. Though the gamut rangethat can be depicted under this specification is not wide (i.e. 72% of the NTSC gamut), it isapproximately the same as that of the BT.709 specification. The BT.709 specification is widely used forhigh-definition television (HDTV) and Blu-ray disc (BD).
3. Adobe RGB Specification
While the gamut range that can be depicted under this specification is close to that of the NTSC
specification, the coverage is slightly different. This is not an international specification. However, it isaccepted as a de facto standard in the printing and publishing industries. Many computer monitors,
printers, and digital devices such as digital cameras also follow this specification.
4. BT.2020 Specification
A specification for a high dynamic range (HDR) for the next generation 4K/8K broadcasting and Ultra
HD Blu-ray disc (UHD BD). The gamut range that can be depicted under this specification is very wide.
While the conventional HDTV specification, BT.709, can only reproduce 74.4% of all the surface colors
seen in nature, this specification can reproduce 99.9%.
As shown in Figure 2, the color gamut range that can be depicted using LEDs is wider than the range
covered by the NTSC specification or the Adobe RGB specification. This means that when compared tofamiliar personal full color display devices (i.e. color televisions and computer monitors) LEDs have acomparable or even better color reproduction.

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Application Note
0.9
0.8
0.7

― 1. NTSC gamut

0.5― 2. sRGB gamut

0.4― 3. Adobe RGB gamuty

0.6― 4. BT.2020 gamut

0.3… LED(x19B-V1) gamut

0.2

0
0

0.1

0.2

0.3

0.4
x

0.5

0.6

0.7

0.8

Figure 2. Comparison of the gamut ranges of LEDs and major color gamut specifications

4. Additive color mixing vs. subtractive color mixing
The process of combining two or more primary colors to produce another color is called color mixing.
Different colors can be created by changing combinations of the colors and their mixing ratio. There are
two types of color mixing: additive and subtractive as described below.
4.1. Additive color mixing
In additive color mixing, a new color is created by adding different colors together. The three primarycolors used in additive color mixing are red, green, and blue. This method applies to computer monitors,
color tunable lighting, etc. to produce colored light. The more colors that are mixed, the brighter the
produced color becomes; when all three primary colors are added together, white light is produced. Figure
3 shows a reference image of additive color mixing.
Example: As shown in Figure 4, adding red and blue light produces magenta light. The magenta light
has a wavelength that contains both red and blue light.
B

G＋
Wavelength
波長

Figure 3. Reference image

B

B

＝

Intensity
強度

R

Wavelength
波長

R

Intensity
強度

R

Intensity
強度

Light Emitting Diode

0.1

Wavelength
波長

Figure 4. An example of additive color mixingof additive color mixing
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Application Note
4.2. Subtractive color mixing
In subtractive color mixing, a new color is created by adding differently colored materials that reflect
certain colors (i.e. printer inks, color filters, etc.). The three primary colors in subtractive color mixing arecyan, magenta, and yellow. Contrary to additive color mixing system, in subtractive color mixing the morecolors that are mixed, the darker the produced color becomes. Figure 5 shows a reference image ofsubtractive color mixing.
Example: As shown in Figure 6, when a cyan and yellow color filter are used together, the cyan filter
absorbs the wavelength in the red region and the yellow filter absorbs the wavelength in the blue
region; only the green wavelength is transmitted to produce green light.

Light Emitting Diode

White Light
C
M

Y

R
G

G
B

Cyan color filter
absorbing red

Figure 5. Reference image

Yellow color filter
absorbing blue

Figure 6. An example of subtractive color mixing

of subtractive color mixing

5. Color mixing designs using LEDs (i.e. additive color mixing)
5.1. Method of color mixing
The method used for color mixing with LEDs is additive color mixing. For additive color mixing withtristimulus values X, Y, and Z in the CIE 1931 XYZ color space5, the mixed color light can be expressed as
the sum of the tristimulus values for the component of each primary color light.
The tristimulus values of the mixed color light are derived using the equations below equation 1; where
the tristimulus values for the nth LED (i.e. LEDn) are expressed as Xn, Yn, and Zn respectively. For example,
the tristimulus values for the 1st LED (i.e. LED1) are expressed as X1, Y1, and Z1, those for the 2nd LED (i.e.
LED2) as X2, Y2, and Z2, those for the 3rd LED (i.e. LED3) as X3, Y3, and Z3, etc.
𝑋 = 𝑋1 + 𝑋2 + 𝑋3 + ・・・ + 𝑋𝑛
𝑌 = 𝑌1 + 𝑌2 + 𝑌3 + ・・・ + 𝑌𝑛

Equation 1

𝑍 = 𝑍1 + 𝑍2 + 𝑍3 + ・・・ + 𝑍𝑛

Note:
5

See the XYZ color space in the CIE 1931 Standard for details.

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Application Note
Equation 2 shows the relationships among the tristimulus values, the chromaticity coordinates (x, y), andthe brightness (i.e. luminous flux or luminance).

𝑋=

𝑌
𝑥
𝑦
Equation 2

𝑌 = 𝑌 Brightness (i.e. luminous flux or luminance)𝑍=𝑌(1 − 𝑥 − 𝑦)𝑦Using equations 1 and 2 above, the chromaticity and brightness of the mixed color light can be calculated
if the chromaticity and brightness of the primary color light are known, and vice versa. That means thatthe brightness required for each color LED will be known once the required chromaticity and brightness

Light Emitting Diodefor the mixed color light are specified.
5.2. Example of color mixing calculation
Using Nichia E17A series LEDs, Nichia provides an example
Target:5000K, 100 lm

calculation of how bright each discrete color LED should be to
produce a required chromaticity and brightness.
The LEDs used for this calculation are as follows: one piece ofY1 (lm)NCSRE17A LED (red), one piece of NCSGE17A LED (green), andY2 (lm)Y3 (lm)one piece of NCSCE17A LED (royal blue).
The required chromaticity coordinate for the mixed color lightis (x, y) = (0.345, 0.355).

Figure 7. Concept for the calculation

The required brightness for the mixed color light is 100 lm.
Figure 7 shows the concept for the example calculation.
Table 2 shows the typical chromaticity coordinates (x, y) for the E17A series LEDs. In this table, thebrightness of the LEDs are variables and expressed as Y1, Y2, and Y3.
Table 2. Chromaticity coordinates for the E17A and target
Chromaticity coordinates

Brightness

ｘ

ｙ

Y

NCSRE17A (Red)

0.683

0.313

Y1

NCSGE17A (Green)

0.252

0.651

Y2

NCSCE17A (Royal Blue)

0.157

0.021

Y3

Target: 5000K

0.345

0.355

100 lmTo find the tristimulus values (X, Y, and Z) for each LED, those values from Table 2 are substituted into theequations 2; see Table 3.

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Application Note
Table 3. Calculated tristimulus values
Tristimulus Values
X

YZ

NCSRE17A (Red)

2.182 Y1

Y1

0.013 Y1NCSGE17A (Green)

0.387 Y2

Y2

0.149 Y2NCSCE17A (Royal Blue)7.476 Y3

Y3

39.143 Y3Target: 5000K

97.183100

84.507

Substituting the calculated tristimulus values from Table 3 into the equations 1 derives the system of
equations 3 as below.

Light Emitting Diode97.183 = 2.182𝑌1 + 0.387𝑌2 + 7.476𝑌3
100 = 𝑌1 + 𝑌2 + 𝑌3

Equation 3

84.507 = 0.013𝑌1 + 0.149𝑌2 + 39.143𝑌3
By solving these equations 3 it is possible to determine the brightness required for each LED: Y 1, Y2, andY3. In this example, the values are Y1 (red) =25.2 lm, Y2 (green) = 72.9 lm, and Y3 (royal blue) = 1.9 lm.
This example shows how to create a new color with three different colors; the same method applies whencreating a mixed color with two colors (i.e. two white LEDs: one with a high color temperature and theother with a low color temperature). When using this calculation method for color mixing with four ormore colors, ensure that the brightness for one or more color(s) is specified in equation 1 so that there
are not more than three variables. Note that when mixing four or more colors, there will be more than
one combination of brightness for each color to create a certain color.

6. General cautions/suggestions for using the LEDs
When designing full-color luminaires using discrete color LEDs, the following must be considered:‧ The absolute maximum rated forward current must not be exceeded for any of the LEDs in theluminaire under any circumstances.
‧ The absolute maximum rated junction temperature must not be exceeded for any of the LEDs in theluminaire under any circumstances.
‧ Each LED has its own current and temperature characteristics; the measured values of luminous
flux/chromaticity may be different from the designed values when the LEDs are operated in luminaires.
‧ When designing the power supply circuit and LED circuit, note that for some LED series, there may
be significant difference in forward voltage (VF) among the different color LEDs; ensure that there are
no issues.
‧ Depending on the design of the luminaire, the color of the light may not be uniform on theilluminated surface (i.e. the emitted colors from the LEDs are not mixed and there are different color
patches on the illuminated surface). Perform sufficient verification to ensure that there are no issues
with the chosen luminaire before use.
‧ Refer to the technical information related to the selected LED series for the assembly precautions.

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Application Note
7. Summary
This application note has provided an example of designing with color mixing for reference purposes only
and Nichia makes no guarantee that customers will see the same results for their chosen application.

Light Emitting Diode

Sufficient verification must be done prior to use to ensure there are no issues for the chosen application.

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Application Note

Light Emitting Diode

Disclaimer
This application note is a controlled document of Nichia Corporation (Nichia) published toprovide technical information/data for reference purposes only. By using this applicationnote, the user agrees to the following: This application note has been prepared solely for reference on the subject matters
incorporated within it and Nichia makes no guarantee that customers will see the same
results for their chosen application.
 The information/data contained herein are only typical examples of performances and/or
applications for the product. Nichia does not provide any guarantees or grant any licenseunder or immunity from any intellectual property rights or other rights held by Nichia or
third parties.
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Phone: +81-884-22-2311 Fax: +81-884-21-0148

NICHIA CORPORATION
http://www.nichia.co.jp

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