Luminous intensity: from Volt to Candela/m2

In summary, the conversation discusses using a probe to convert optical power to an electrical current for the purpose of measuring the brightness of a monitor. The sensor used is a photodiode and the conversion requires using the voltage provided by the sensor, the load resistance, and the responsivity. The expected conversion result is 350cd/m2, but the actual value is incorrect. The use of steradians is suggested for a correct conversion.
  • #1
AlexSuomi
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Homework Statement


I use a probe for converting optical power to an electrical current. I need to convert Volt to candela/m2.
The sensor, a photodiode, measure the brightness of the monitor leaning the probe on the glass (so there is no distance between the monitor and the sensor).
The sensor provides the voltage (0.4V).
Load resistance: 50 omega, Responsivity (0.725 A/W), diameter sensor (0.009 m).
I expect that the conversion will give me 350cd/m2, in fact it is the maximum value of brightness of my monitor.

Sensor: http://www.thorlabs.de/thorcat/TTN/SM1PD1B-SpecSheet.pdf
Vout = P * Responsivity * RL = current * RL

Homework Equations

The Attempt at a Solution


I have tried to use the illuminance responsivity Rvi = Area * Responsivity;
and luminous intensity Iv (cd) = distance^2 * current / Rvi but the value is not correct.
I guess I need to use steradians
 

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  • #2
but I don't know how to use it.I would be grateful if you help me to understand the conversion of voltage to luminance.Thank you
 

1. What is luminous intensity and how is it measured?

Luminous intensity is the measure of the amount of visible light that is emitted from a source in a particular direction. It is measured in units of candela (cd) and can be measured using a photometer or other light-measuring instrument.

2. How is luminous intensity related to voltage?

Luminous intensity is not directly related to voltage. Voltage is a measure of electrical potential difference, while luminous intensity is a measure of visible light. However, the intensity of light emitted from a source can be affected by the voltage that is used to power it.

3. What is the difference between luminous intensity and luminous flux?

Luminous intensity and luminous flux are related but different concepts. Luminous intensity measures the amount of visible light emitted in a specific direction, while luminous flux measures the total amount of visible light emitted from a source in all directions. Luminous flux is measured in units of lumens (lm), while luminous intensity is measured in candela (cd).

4. How does luminous intensity affect the brightness of a light source?

Luminous intensity is directly related to the perceived brightness of a light source. The higher the luminous intensity, the brighter the light will appear. However, other factors such as the distance from the source and the direction of the light also affect the perceived brightness.

5. Can luminous intensity be converted to other units of measurement?

Yes, luminous intensity can be converted to other units such as lumens or lux. One candela is equal to one lumen per steradian (lm/sr) and one lux is equal to one lumen per square meter (lm/m^2). Conversion between these units can be done using mathematical equations or online conversion calculators.

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