# Backing-out luminosity togo from lumens to radiant flux in W

• Andy Kellett
In summary, backing-out luminosity allows for the conversion from lumens to radiant flux in order to measure the total energy emitted by a light source. This process takes into account the sensitivity of the human eye to different wavelengths of light and provides a more accurate measurement of the actual light output of a source. This is important for various industries, such as lighting design and energy efficiency calculations, as it allows for a better understanding of the true brightness and efficiency of a light source.
Andy Kellett
Hi. Has anyone already done the work to back out the standard luminosity function so I can go from lumens at a particular wavelength to radiant flux in Watts? I have visible LED spec sheets with optical characteristics in lumens and I want to calculate the outputs in W. My NIR LED has specs in radiant flux in W because we can't see that. I want everything in W. I found the expression for the standard luminosity function here
https://en.wikipedia.org/wiki/Luminosity_function
but was hoping someone knew of a website or program that already does this.
Thanks!

berkeman
Andy Kellett said:
Hi. Has anyone already done the work to back out the standard luminosity function so I can go from lumens at a particular wavelength to radiant flux in Watts? I have visible LED spec sheets with optical characteristics in lumens and I want to calculate the outputs in W. My NIR LED has specs in radiant flux in W because we can't see that. I want everything in W. I found the expression for the standard luminosity function here
https://en.wikipedia.org/wiki/Luminosity_function
but was hoping someone knew of a website or program that already does this.
Thanks!
Wikipedia says a Lumen is 1/683 Watt measured at 555 nm (green).
What pity illumination engineers do not simply use the same units as radio engineers - Transmitted Power and Isotropic Effective Radiated Power (EIRP) etc.

Andy Kellett
tech99 said:
Wikipedia says a Lumen is 1/683 Watt measured at 555 nm (green).
What pity illumination engineers do not simply use the same units as radio engineers - Transmitted Power and Isotropic Effective Radiated Power (EIRP) etc.

Yes - I know why lighting engineers are concerned with the response of the human eye, but I'm exciting silicon! I will probably just back this out from blue to NIR and share with the group. Thanks for your response and help.

## 1. How do you convert lumens to radiant flux in watts?

To convert lumens to radiant flux in watts, you can use the formula: Watts = lumens/efficacy. Efficacy is a measure of how efficient a light source is at converting electrical energy into light. It is typically measured in lumens per watt (lm/W). This formula can be used to back out the luminosity of a light source to determine the radiant flux in watts.

## 2. What is the difference between lumens and radiant flux in watts?

Lumens and radiant flux in watts are both units of measurement for light, but they measure different aspects of light. Lumens measure the total amount of visible light emitted by a light source, while radiant flux in watts measures the total amount of electromagnetic energy emitted by a light source, including both visible and non-visible light. Lumens are used to describe the brightness of a light source, while radiant flux in watts is used to describe the total power output of a light source.

## 3. Why is it important to back out luminosity to convert lumens to radiant flux in watts?

Backing out luminosity is important because it allows us to accurately determine the radiant flux in watts of a light source. This is useful for understanding the total energy output of a light source and comparing the efficiency of different light sources. It also allows us to calculate the total power consumption of a light source, which is important for energy efficiency considerations.

## 4. Can you convert lumens to radiant flux in watts for any type of light source?

Yes, you can convert lumens to radiant flux in watts for any type of light source as long as you know the efficacy of the light source. Different types of light sources have different efficacies, so it is important to use the correct efficacy value for the specific light source you are converting.

## 5. How can I find the efficacy of a light source to use for converting lumens to radiant flux in watts?

The efficacy of a light source can typically be found on the product label or in the product specifications. It is also available from the manufacturer or can be found through online research. Be sure to use the correct efficacy value for the specific light source you are converting to ensure accuracy in the conversion.

Replies
6
Views
1K
Replies
25
Views
4K
Replies
17
Views
4K
Replies
10
Views
7K
Replies
1
Views
420
Replies
1
Views
3K
Replies
1
Views
3K
Replies
1
Views
3K
Replies
1
Views
2K
Replies
1
Views
8K