# Homework Help: Luminous intensity: from Volt to Candela/m2

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1. Nov 24, 2015

### AlexSuomi

1. The problem statement, all variables and given/known data
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
2. Relevant equations

3. 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

#### Attached Files:

• ###### candela-m2 (1).xlsx
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5.3 KB
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Last edited by a moderator: Nov 24, 2015
2. Nov 29, 2015