Photometric and Radiometric measurement concepts

In summary, the conversation discusses the challenges of converting sensor output into relevant photometric and radiometric quantities, such as wavelength, irradiance, and illuminance. The speakers also mention the importance of understanding the spectral response of the sensor and the limitations of using only the voltage or current output without knowledge of the spectral content of the illumination. They discuss possible formulas and references for converting the sensor output and designing a light meter for various measurements.
  • #1
Aditya Mittal
4
0
Hello,
I am trying to understand the concepts of photometric and radiometric measurements in an electronic sensor. Various photo sensors based on CCD (Charged Coupled Devices) or CMOS photo diode array technology are available in the market for measurements in Visible Spectrum. Now I want to know if there are any generic formulae or functions available to convert the sensor output (analog/digital) into relevant photometric or radiometric quantity such as wavelength or irradiance or Illuminance etc.
 
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  • #2
Without knowing the spectral response of those devices to the whole radiometric interval that you want to measure, I don't think that's possible...
 
  • #3
You mean to say the graphical representation between Wavelength (nm) - x-axis and Responsivity (A/W) - y axis. This information is normally given in data sheet for a particular sensor. So how do I use that information to get the parameters that I need? I have also attached the sample spectral response curve for a typical sensor.
 

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    Spectral Response sample.png
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  • #4
If I understand it correctly, that sensor detects in eight bands from 400 to 700 nm. Between those extreme wavelengths there are gaps with no detection. And, for wavelengths longer than 700 nm, the sensor simply doesn't work at all. The black line in the graphic is probably the transmittance of the sensor's window...
 
  • #5
NTW said:
If I understand it correctly, that sensor detects in eight bands from 400 to 700 nm. Between those extreme wavelengths there are gaps with no detection. And, for wavelengths longer than 700 nm, the sensor simply doesn't work at all. The black line in the graphic is probably the transmittance of the sensor's window...

I don't think so. I think the black curve is the sensor's spectral response. The colored lines look like specific filters that are used when you want to view only a specific part of the spectrum.
 
  • #6
Aditya Mittal said:
Now I want to know if there are any generic formulae or functions available to convert the sensor output (analog/digital) into relevant photometric or radiometric quantity such as wavelength or irradiance or Illuminance etc.

There are. I'll try to find my book on astronomical image processing and see what it says about this. I'm willing to bet it has it in there.
 
  • #7
Aditya Mittal said:
You mean to say the graphical representation between Wavelength (nm) - x-axis and Responsivity (A/W) - y axis. This information is normally given in data sheet for a particular sensor. So how do I use that information to get the parameters that I need? I have also attached the sample spectral response curve for a typical sensor.

Calculating the radiometric quantities (W received, etc) is straightforward from the graph- You start by specifying the (spectral) input radiation, multiply by the (spectral) detector sensitivity and you're basically done.

Calculating the photometric quantities proceeds similarly, but you also multiply the eye's spectral response curve (http://en.wikipedia.org/wiki/Photometry_(optics)#mediaviewer/File:Luminosity.png) to the above calculation to convert watts into lumens.

Is that what you want to do?
 
  • #8
@Andy Resnick - Yes that is true that I want to measure radiometric and photometric quantities from the sensor output. The output of the sensor is preferentially in Volts or Ampere and at most it could be an input to an ADC to get the digital output which can be read by a micro controller section in the circuitry. Now I am still unable to utilize that sensor output.
@Drakkith - It would really be of great help to me if there are any such formulae available in any of the text references that you might have.
@NTW - The response posted by '@Drakkith' is correct to your comment.

In general I want to design a light meter for photopic and scotopic illuminance, EVE factor, luminous color, color rendering index, luminous spectrum. For that I need to first focus on sensor interface and how the output from sensor could be utilized for this.
Also let me know in case you would like to have any other inputs from my end regarding this.
 
  • #9
If you don't have access to the spectral content of your illumination and all you have is the voltage/current output of the sensor, there is no way to perform your calculation.
 

1. What is the difference between photometry and radiometry?

Photometry and radiometry are two branches of optics that deal with the measurement of light. Photometry focuses on the measurement of visible light, while radiometry encompasses all forms of electromagnetic radiation, including visible light, infrared, and ultraviolet.

2. How are photometric and radiometric measurements related?

Photometric and radiometric measurements are related because they both use similar units of measurement, such as lux, candela, and watt. Additionally, photometric quantities, such as luminous flux and illuminance, can be converted to radiometric quantities, such as radiant flux and irradiance, using conversion factors.

3. What is the purpose of photometric and radiometric measurements?

The purpose of photometric and radiometric measurements is to quantify the amount of light or electromagnetic radiation present in a given environment. This information is useful in a variety of applications, such as lighting design, remote sensing, and environmental monitoring.

4. How are photometric and radiometric measurements performed?

Photometric and radiometric measurements are typically performed using specialized instruments, such as photometers or spectrometers. These instruments can measure different properties of light, such as intensity, color, and wavelength, and provide numerical values that can be used for analysis and comparison.

5. What are some common applications of photometric and radiometric measurements?

There are many applications of photometric and radiometric measurements, including lighting design, photography, astronomy, and environmental monitoring. These measurements are also used in industries such as agriculture, healthcare, and manufacturing to ensure proper lighting conditions and radiation levels for optimal performance and safety.

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