Application Note

Light Emitting DiodeHow to Calculate the Junction Temperature
for the Nichia 270 Series LEDs

Table of Contents
1. Overview ........................................................... 2
2. Applicable Part Numbers .................................. 2
3. TMP Measurement .............................................. 3
4. TJ Calculation Method ...................................... 4
5. TJ Calculation Example ..................................... 4
6. Cautions of Attaching Thermocouple ............... 5
7. Summary ........................................................... 5

The Nichia part numbers NJ2W270A, NJ2W270A-Y7, NJ2W270B, NJ3W270B, NJ2W270B-PF
and NJ3W270B-PF within this document are merely Nichia’s part numbers for those Nichia
products and are not related nor bear resemblance to any other company’s product that might bear atrademark.

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-200675-2
1/6
Jun. 14, 2024

Application Note
1. Overview
The thermal management for the LEDs is managed by Junction Temperature (TJ). If TJ value is outof spec. as overheated, it brings negative influence on reliability and might occur No-light mode atthe worst case. This document introduces the method of TJ calculation by measuring the LED outline
temperature with thermocouple.

2. Applicable Part Numbers

Light Emitting Diode

This application note applies to the LEDs shown in Table 1.
Table 1. Applicable LED Part Numbers
NJ2W270A
NJ2W270A-Y7
Part No.

NJ2W270B
NJ3W270B
NJ2W270B-PF
NJ3W270B-PF

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-200675-2
2/6Jun. 14, 2024

Application Note
3. TMP Measurement
TJ calculation is available by measuring the temperature of LED outline as TMP. (See Table 2)

Table 2. TMP measuring point
Part No.

NJ2W270A /NJ2W270A-Y7

NJ2W270B

NJ3W270B●TMP measuring pointNJ2W270B-PF

NJ3W270B-PF

TMP

Light Emitting Diodemeasuringpoint

When measure the temperature of TMP with thermocouple, please attach the sensing point ofthermocouple at the designated position of the ceramics part with fixing material such as a glue.
(See Figure 1)

PCB

TMP measuring point
LED

TMP measuring point
Thermocouple

Thermocouple

Glue
PCB

Glue
LED
（e.g.：NJ2W270B）

Heatsink

Figure 1. TMP measuring method

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-200675-2
3/6Jun. 14, 2024

Application Note
4. TJ Calculation Method
TJ can be calculated with the below formula, combining each necessary parameter including themeasured TMP and others under driven.

TJ = TMP + RθJMP × W……… (1)

TJ = LED junction temperature (℃)
TMP = Temperature of measuring point (℃)
RθJMP = Thermal resistance from LED junction to TMP measuring point (℃/W)

Light Emitting Diode

W = Input power (IF×VF) (W)

RθJMP values are introduced in the below table for each LED type. (See Table 3)

Table 3. RθJMP values
Part No.

RθJMP (℃/W)

NJ2W270A

6.0

NJ2W270A-Y7

6.0

NJ2W270B

5.0

NJ3W270B

4.3

NJ2W270B-PF

5.0

NJ3W270B-PF

4.3

5. TJ Calculation Example
It is introduced the TJ calculated result with the TMP measured result based on TMP measuring method.
(See Figure 1)【Example LED: NJ2W270B】
The TJ value is calculated 120℃ as below with the parameters: TMP=70℃ and Input Power=10W.
(TMP: See Table 3)

TJ = TMP + RθJMP × W
TJ = 70(℃) + 5.0(℃/W) × 10(W) = 120(℃)

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-200675-2
4/6
Jun. 14, 2024

Application Note
6. Cautions of Attaching Thermocouple
When there is a gap from ceramics to thermocouple, or when the thermocouple contacts to otherthan LED ceramics part, the measurement values might have the problem of accuracy with missmeasuring.
The temperature sensing point of thermocouple is the 1st contact point of two wire from root. Whenthe thermocouple has twisting tip (Figure 2-b), the temperature is measured by 1st contact point ofwires, the tip is not sensing point. Even if the tip of thermocouple contacts to LED, if the temperaturesensing point does not contact that the measurement value might be lower.

Light Emitting Diode(a)(b)

Temperature sensing point

Temperature sensing point(c)Temperature sensing point

Figure 2. Temperature sensing point of thermocouple

It needs to care that the glue for fixing thermocouple is not too much. if the glue covered LED
emitting surface, the measurement values might have the problem of measurement accuracy with
miss measurement.

7. Summary
This document introduces the TJ calculation method based on the actual measuring withthermocouple for the mock-up LED module/unit evaluation. The influential parameter as TMP ischangeable depending on thermocouple set-up and PCB conditions as material kind etc. for example.
Please make the precise measuring procedure as much as possible referring the introduced methodin this document. Please ensure to make the proper thermal design to control TJ value within thespecified maximum value in datasheet.

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-200675-2
5/6
Jun. 14, 2024

Application NoteDisclaimer
This application note is a controlled document of Nichia Corporation (Nichia) published to provide
technical information/data for reference purposes only. By using this application note, 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.

Light Emitting Diode・ The information/data contained herein are only typical examples of performances and/orapplications for the product. Nichia does not provide any guarantees or grant any license underor immunity from any intellectual property rights or other rights held by Nichia or third parties.
・ Nichia makes no representation or warranty, express or implied, as to the accuracy, completenessor usefulness of any information contained herein. In addition, Nichia shall not be liable for any
damages or losses arising out of exploiting, using, or downloading or otherwise this document,or any other acts associated with this document.
・ The content of this application note may be changed without any prior or subsequent notice.
・ Copyrights and all other rights regarding the content of this document are reserved by Nichia or
the right holders who have permitted Nichia to use the content. Without prior written consent of
Nichia, republication, reproduction, and/or redistribution of the content of this document in any
form or by any means, whether in whole or in part, including modifications or derivative works
hereof, is strictly prohibited.

491 Oka, Kaminaka-Cho, Anan-Shi,
TOKUSHIMA 774-8601, JAPAN
Phone: +81-884-22-2311 Fax: +81-884-21-0148

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

This document contains tentative information, Nichia may change the contents without notice.
SP-QR-C2-200675-2
6/6Jun. 14, 2024