Application Note

Light Emitting Diode

Guideline for Using the Easy Estimation
Tool to Calculate Luminous Flux

Table of contents
1. Overview ........................................................................2
2. Structure of a Typical LED Retrofit Lamp ............2
3. Evaluation of LED Tube Performance ...................6
4. Estimation for LED Down Light ..............................95. Evaluation of LED Down Light Performance ... 11
6. Summary ..................................................................... 14

The part number NFSW757D-V1 and NFSL757D-V1 in this document are
the part number of Nichia’s products, and do not have any relevance orsimilarity to other companies' products that may have trademark rights.

This document contains tentative information, Nichia may change the contents without notice.
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Application Note
1. Overview
This application note describes the guidelines to estimate the optical characteristics (luminous
flux/efficiency) of LED-mounted fixtures (tubes and down lights) using the “Easy Estimation Tool.” Pleaserefer to the “Easy Estimation Tool Guide” for detailed usage of the estimation tool.

2. Structure of a Typical LED Retrofit Lamp
2.1. Determination of Product SpecificationsFirst of all, determine the target values for product specifications such as the luminous flux and theconsumption power. Regarding the luminous flux and the efficiency, take the luminous flux decrease dueto the optical cover into account to set their target values. The operating voltage/current are sometimes

Light Emitting Diodespecified depending on the standard which applies to the product; in such a case, select the appropriate
power supply to make it possible to operate the LEDs within the standard.
We designed the LED tube in accordance with “JEL801” specified by the Japan Lighting Manufacturers
Association.
Target Values
Outline:1,200mm

Luminous Flux:

2,300lm or more

Efficiency:

145lm/W or more

Color Temperature:

5,000K

Average Color Rendering Index (Ra):80 or more

Input Power:

Voltage; DC45 to 95V, Current; 350mA
in accordance with JEL801

Rectifying Bridge Diode: Loss of electrical power
Optical Cover
LED-Mounted Board

Figure 1. LED Tube StructureThis document contains tentative information, Nichia may change the contents without notice.
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Application Note
2.2. Calculation with Easy Estimation Tool
Fill out the information in each item in the simulation tool.

2.2.1. LED Series and Model
Select the LED “Series” and ”Type” in the simulation system (cf. Enclosed in blue 1 in Figure 2). Here is only
one estimation example using NFSW757D-V1. In fact, in each Excel spreadsheet, there can be found thecalculation results for five types at a time, where you will be able to compare values among them.
As described in Section 2.1, the target value of the color rendering index is Ra>80. Therefore, we chose
R8000 for the simulation.

2.2.2. Parameters

Light Emitting Diode

Fill out the parameters which are necessary to estimate the optical characteristics (cf. Enclosed in blue 2
in Figure 2).
Table 1. Input Information for the Simulation
Item

Note

Input Examples

Target Flux

Target values of luminous flux

2,400lm (Target; 2,300lm＋margin)

Color Rank

LED’s color rank

For 5,000K, choose sw50.

Junction Temperature: TJ

Estimated LED’s junction

50°C, as reference to LED tubes withtemperature

the same power/structure

Output loss due to optical

Fill out the luminous flux decrease rate

covers, etc.

resulting from the cover; i.e. 10%

Power consumed in theFill out 3.7%; consumed by thecircuits other than LEDs’

rectifying bridge diode

Quantity of LEDs used for theFill out arbitrary numbers; they should

product

be corrected later.

Optical Efficiency Loss
Electrical Efficiency Loss
LED Multiple

2.2.3. Estimation of Amount of LEDs
When the maximum input current is filled out in “Forward Current IFP“ (Enclosed in blue 3 in Figure 2), thecharacteristics can be calculated at each specific range (cf. Enclosed in red in Figure 2). Please note thatthe input IFP below the table is the value for a single LED.
Next, the amount of LEDs (LED Multiple) can be calculated so that the LED tube’s target values of theluminous flux, the power consumption, and the optical efficiency can be achieved at a specific input
current.
Let us simulate the LED multiple using 757D-V1 as follows:
1) Determine the current applied to each LED which accomplishes the target efficiency (145lm/W ormore), judging from the obtained values of “lm/W” (cf. Enclosed in red in Figure 2). As shown inthe values in the table, the luminous efficiency of the LED tube will achieve 145lm/W or more unlessthe input current exceeds IFP =65mA.
The lower the current is applied to the LEDs, the higher the efficiency of the tube increases, on thebasis of the LEDs’ characteristics.
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Application Note
The “LED Multiple (quantity of LEDs)” does not have to be determined at this point, since it is not
related with the efficiency of the LED tube.
2) Based on the estimated maximum input current (IFP =65mA) and the output current (350mA) of thepower supply, the current applied to each LED will be IFP =35mA. Then, the drive circuit can beobtained as follows: 350mA / 35mA = 10 parallel circuits
3) Assuming that the LEDs are connected in 10 parallel circuits, let us determine the “LED Multiple”,
increasing it by 10 pieces. The “LED Multiple” should achieve the target luminous flux of 2,400lm
at IFP =35mA. The luminous flux will be 2,473.9lm, when the quantity of LEDs is 160 pieces, whichaccomplishes the target luminous flux. Thus, the quantity of LEDs needs to be 160 pieces; 16 series
and 10 parallel for an LED tube.

2

Light Emitting Diode

1

2

3

4

Characteristics
obtained after lm andVF are filled out in 4
(enclose in blue).
Figure 2. Example of Calculation
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Application Note
2.3. Impact of Variation in the Luminous Flux on the Simulation
In the Easy Estimation Tool, typical values of the luminous flux/forward voltage specified for each LED typeare used. Therefore, the luminous flux and the forward voltage vary even within the same rank.
When you fill out “lm” or “VF” (Enclosed in blue 4 in Figure 2), the LEDs’ characteristics can be calculated
at the rated luminous flux/forward voltage (rated current). Then, you can obtain the minimum/maximum
luminous flux/power (efficiency) of the LEDs installed in the tube. Be sure to confirm whether theminimum/maximum values are within the tolerance specified for the LED tube.

2.4. Preparation of LED Tube
We prepared a sample LED tube in accordance with the specifications determined through Section 2.1
and the characteristics calculated through Section 2.2. The LED specifications are as follows:

Light Emitting DiodeLED Specifications
Part No.:

NFSW757D-V1

Quantity:

160 pcs. (16 series and 10 parallel)

Luminous Flux:

31.25lm at 65mA applied to each LED(average value of 50 sampled-out pieces)VF:

2.93V at 65mA applied to each LED(average value of 50 sampled-out pieces)

25

25

20

20

15
10

15
10

0
31.5 32.0

0

31.0 31.5

5
30.5 31.0

52.90 - 2.91

Qty [pcs]

30

30.0 30.5

Qty [pcs]

3530

Luminous Flux [lm]average: 2.93 [V]
If=65mA, Sample size= 50 pcs

2.95 - 2.96

average: 31.25 [lm]If=65mA, Sample size= 50 pcs

35

2.94 - 2.95

R8000 (Ra>80)

2.93 - 2.94

Color Rendering Rank:

2.92 - 2.93

sw50 (5,000K)

2.91 - 2.92

Color Rank:

Vf [V]

Figure 3. LED’s Luminous Flux and VF (50 Sampled-out LEDs)

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Application Note
3. Evaluation of LED Tube Performance
The performance of the LED tube prepared in Section 2.4 has to be evaluated to confirm whether there is
any significant difference between the actual values and the calculation. If there are any significant
differences between them, it is necessary to review the parameters and recalculate the values.

3.1. Electrical/Optical Characteristics
The LED tube’s power consumption is measured with a power measurement device and its luminous flux
is measured with a sphere. Be sure to operate the LED tube until the heat is saturated and until themeasurement results stabilize.

Light Emitting Diode

Measurement Results of Sample LED Tube
Power Consumption:

16.1W

Luminous Flux:

2,412lm

Efficiency:

150lm/W

3.2. Thermal Factor
3.2.1. Thermal Distribution
The heat distribution on the board is measured with a thermometer while the heat is saturated in the tube.
If the thermal distribution is inhomogeneous, the LEDs’ junction temperatures may vary depending on
their location. Then, the LEDs’ brightness may vary due to their thermal characteristics. Consequently, it isdifficult to evaluate the LED tube characteristics.
As seen in Figure 4, there is no problem in the thermal distribution in the LED tube: the heat ishomogeneously dissipated in the tube.

Figure 4. Thermal Distribution in the LED Tube

3.2.1. Thermal Distribution
The junction temperature can be calculated by the soldering temperature (cf. Equation 1). Whenmeasuring the soldering temperature, saturate the heat within the tube after fixing the thermocouples tothe LED leads with solder or adhesive agent.
Be sure to measure the soldering temperature in the finished product; in a closed environment within the
housing by attaching an optical cover, etc.
Thermal design of LED tubes should not exceed the LEDs’ absolute maximum rating.
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Application Note
LED Junction Temperature

TJ= TS + RΘJS W
where(Equation 1),
TS: Soldering temperature (°C),
RΘJS: Thermal resistance from the LED die to the Ts measuring point (°C/W)
W: Power supply to each LED; IF ˣ VF (W)Measurement Results of Sample LED Tube
TS (Soldering Temperature): 46.2°C
TJ (Junction Temperature): 46.2°C + 13°C/W ˣ 0.1W = 47.5°C
whereRΘJS= 13°C/W * Specified for the LEDs
W= 2.9V ˣ 35mA = 0.1W

Light Emitting Diode3.3. Comparison between the Measured/Calculated Values
Let’s compare the measured values and the calculated ones.
Table 2. Comparison of Measurement and Calculation
Calculated

Measured

Difference

Tube Luminous Flux

2,474lm

2,412lm-2.5%

Tube Efficiency

155lm/W

150lm/W-3.2%

Both the tube luminous flux/efficiency met the target values; however, the measured values were below
the calculated ones. The difference of 5lm/W is relatively large, which may affect the LED tube performance.
Therefore, the measurement conditions should be reviewed and the measurement results should be
evaluated again.
The junction temperature was 47.5°C, based on the measurement results. According to the LED
specifications (cf. Section 2.4), the luminous flux and the VF were 31.25lm and 2.93V per LED, respectively.
Therefore, the measurement parameters were corrected as follows:
Table 3. Parameters and Measurement Values
Before Corrected

After CorrectedElectrical current applied to each LED

35mA

35mA

Junction Temperature

50.0°C

47.5°C

Optical Loss

10%

10%

Electrical Loss

3.7%

3.7%

Qty of LEDs

160pcs.

160pcs.

Luminous Flux per LED

32.0lm (Typ.)31.25lm

VF per LED

2.90V (Typ.)

2.93V

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Light Emitting Diode

Application Note

Figure 5. Re-calculation of LED Tube
Let us compare the recalculation results and the measurement ones.
Table 4. Comparison of Recalculation Results and Measurement Results
Calculated

Measured

Difference

Tube Luminous Flux

2,424lm

2,412lm-0.5%

Tube Efficiency

151lm/W

150lm/W-0.7%

The differences in both the tube luminous flux/efficiency became much smaller; therefore, the LED tube
was designed in accordance with the calculation after the parameter correction.

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Application Note
4. Estimation for LED Down Light
4.1. Determination of Product SpecificationsFirst of all, determine the target values for product specifications such as the luminous flux and theconsumption power. We designed an LED down light to achieve the following specifications.
Target Values
Luminous Flux:

370lm or more

Color Temperature:

2,700K

Average Color Rendering Index (Ra):80 or more

Circuit:

12 LEDs connected (4series and 3parallel)

Input Power:

DC 330mA (The electrical current of 110 mA is flown into per

Light Emitting Diode

LED, since 3 LEDs are connected in parallel.)Lamp Cover

Light Diffusing Panel
Optical Reflector
LED-Mounted Board
Figure 6. LED Tube Structure

4.2. Calculation with Easy Estimation Tool
Fill out the information in each item in the simulation tool as described in Section 2.2.

4.2.1. LED Series and TypeWe used one of the same series with a different color (NFSL757D-V1) for the LED down light.
As described in Section 4.1, the target value of the color rendering index is Ra>80. Therefore, we chose
R8000 for the simulation.

4.2.2. Parameters
Fill out the parameters which are necessary to estimate the performance.

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Application Note
Table 5. Input Information for the Simulation
Item

Note

Input Examples

Target Flux

Target values of luminous flux

370lm

Color Rank

LED’s color rank

For 2,700K, choose sw27.

Junction Temperature: TJ

Estimated LED’s junction

50°C, as reference to LED down lighttemperature

with the same power/structure

Output loss due to optical

Fill out the luminous flux decrease rate

covers, etc.

resulting from the cover; i.e. 19.3%

Power consumed in the

No electrical loss

Optical Efficiency Loss
Electrical Efficiency Losscircuits other than LEDs’
LED Multiple

Quantity of LEDs used for the

12 pcs.

Light Emitting Diodeproduct

4.2.3. Calculation
Figure 7 shows that the luminous flux meets (reaches) the target specifications; 370lm.

The operating power supply is 330mA
and 3 LEDs are connected in parallel;
therefore, the electrical current flown
into each LED should be 110 mA.

Figure 7. Example of Calculation (LED Down Light)

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Application Note
4.3. Preparation of LED Down Light
We prepared for a sample LED down light in accordance with the target specifications, using the LEDs
with the following specifications:
LED Specifications
Part No.:NFSL757D-V1

Quantity:

12 pcs. (4 series and 3 parallel)

Luminous Flux:

27.18lm(avg.) at 65mA applied to each LED

VF:

2.93V(avg.) at 65mA applied to each LED

Color Rank:

sw27 (2,700K)

Color Rendering Rank:

R8000 (Ra>80)

average: 27.18 [lm]If=65mA, Sample size= 12 pcs

12

10

10

8

8

Quantity [pcs]

6
4
2

6
4
2

Luminous Flux [lm]2.95 - 2.96

2.94 - 2.95

2.93 - 2.94

2.92 - 2.93

27.5 - 28.0

27.0 - 27.5

26.5 - 27.0

26.0 - 26.5

2.91 - 2.92

002.90 - 2.91

Quantity [pcs]Light Emitting Diode12

average: 2.93 [V]
If=65mA, Sample size= 12 pcs

Vf [V]

Figure 8. LED’s Luminous Flux and VF (12 LEDs)

5. Evaluation of LED Down Light Performance
5.1. Electrical/Optical Characteristics
Let us measure the electrical/optical characteristics of the LED down light prepared in Section 4.
Measurement Results of Sample LED Down LightPower Consumption:

4.0W

Luminous Flux:

409lm

Efficiency:

101lm/W

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Application Note
5.2. Thermal Factor
The soldering temperature was measured with a thermocouple and the junction temperature wascalculated.
Measurement Results of Sample LED Down LightTS (Soldering Temperature): 47.4°C
TJ (Junction Temperature): 47.4°C + 13°C/W ˣ 0.32W = 51.6°C
whereRΘJS= 13°C/W * Specified for the LEDs
W= 2.9V ˣ 110mA = 0.32W

5.3. Comparison between the Measured/Calculated Values

Light Emitting Diode

Let’s compare the measured values and the calculated ones.
Table 6. Comparison of Measurement and Calculation
Calculated

Measured

Difference

Tube Luminous Flux

391lm

409lm

+4.6%

Tube Efficiency

99lm/W

101lm/W+2.0%

There was a slight difference between the measured and the calculated values.
Therefore, the measurement conditions should be reviewed and the measurement results should be
evaluated again.
The LED junction temperature was 51.6°C, based on the measurement results. According to the LED
specifications (cf. Section 4.3), the luminous flux and the VF were 27.18lm and 2.93V per LED, respectively.
Therefore, the measurement parameters were corrected as follows:
Table 7. Parameters and Measurement Values
Before Corrected

After CorrectedElectrical current applied to each LED

110mA

110mA

Junction Temperature

50.0°C

51.6°C

Optical Loss

19.3%

19.3%

Electrical Loss0%0%

Qty of LEDs

12pcs.

12pcs.

Luminous Flux per LED

25.9lm (Typ.)27.18lm

VF per LED

2.90V (Typ.)

2.93V

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Light Emitting Diode

Application Note

Figure 9. Re-Calculation of LED Down Light
Let us compare the recalculation results and the measurement ones.
Table 8 Comparison of Recalculation Results and Measurement Results
Calculated

Measured

Difference

Tube Luminous Flux

409lm

409lm

0%

Tube Efficiency

102lm/W

101lm/W-1.0%

There was no difference in the lamp luminous flux between the recalculated and the measured values.
The difference in the lamp efficiency became much smaller; therefore, the LED down light was designedin accordance with the calculation.

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Application Note
6. Summary
Design validation is critical when LEDs are installed into lighting fixtures. The performance should bevalidated by comparison between the calculated/measured values.
There is no significant difference between the measured / calculated values on this simulation, as long as
the simulation is used for LEDs mounted on the board; however, you may not obtain the expected values
for the lighting fixture due to optical/electrical loss resulting from the component materials and/or the
fixture’s structure.
In such cases, re-measure the performance after changing the parameters of the optical/electrical loss.
If it is difficult to measure the performance, such as the luminous flux and the VF, because of the fixture’s
structure, it should be calculated and measured for the LEDs mounted on the board.
In this document, we used the typical thermal resistance RΘJS described by the specifications to calculateLight Emitting Diodethe LEDs’ junction temperature; however, the characteristics vary when LEDs are installed in lighting
fixtures.
As LEDs’ junction temperature increases, in general, the light output reduces. Therefore, it is necessary to
set the target luminous flux to ensure that the expected value is obtained even at the maximum thermal
resistance.
Moreover, the forward voltage and the luminous flux vary even within the same rank. Therefore, assumingthat the LEDs’ characteristics are distributed at the minimum/maximum within the same rank, you should
design lighting fixtures that ensure the expected values are within the specifications.

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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.
 Nichia makes no representation or warranty, express or implied, as to the accuracy,completeness or usefulness of any information contained herein. In addition, Nichia shallnot be liable for any damages or losses arising out of exploiting, using, or downloadingor 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 priorwritten consent of Nichia, republication, reproduction, and/or redistribution of thecontent 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.

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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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