# Radiometry, photocurrent in optics simulation

1. Nov 26, 2014

### vst98

Hi all,

I have to estimate a photocurrent produced in the following simulation setup.
Photodiode (detector) and LED (spaced 2cm) lie on one axis, oriented toward a wall (radiometer film) which is parallel to the axis and at a distance of about 10cm from the axis. How much photocurrent would an area dAw of the wall produce on the photodiode if irradiance on dAw received from the LED is known.

Further details:
- The photodiode and LED don't point directly to the wall but are tilted to 70 degrees.
- Irradiance on the dAw is in the order of 10-3 W/cm2, I will assume that the wall is totally reflecting and behaves like Lambertian scatterer.
- Geometry is known, that is detector (photodiode) area, dAw area, their distance and normal angles to the connection line are known.

It seems to me that I could use

$$\phi_1 = L_1\frac{dA_1*cos\theta_1*dA_2*cos\theta_2}{r^{2}}$$

$$L_1 = \frac{I_1 }{dA_1*cos\theta_1}$$

Φ1 is the flux (power) recieved by the photodiode of detector area dA1 , dA2 is the area of the
wall elment, θ1 and θ2 are angles normals of the dA1 and dA2 make with connecting line r.

If I could supstitute radiance L1 in the equation for the Φ1 I could get to the photocurrent, but L1 is expressed in terms of intensity I1 emitted from the
wall element dA1 which is in [W/sr] units and I know iradiance E, which is [W/m2].
so I got stuck here.

There is also another way I can aproach this problem. In simulation, I can turn the photodiode to be a source,
and get irradiance on the same dAw element from the photodiode-source and from the LED. But im not sure if i could use this somehow to estimate the photocurrent.

Last edited: Nov 26, 2014
2. Nov 28, 2014

### vst98

I'll try again to explain my problem clearly.
If I found irradiance on the wall element dAw from the LED diode to be Eled and
then independently found irradiance on the same dAw from the photodiode to be Epd
(I can make a detector area of the photodiode to be a source of rays in simulation).
Could I estimate power, or anything, which would be received on the photodiode (detector now)
from dAw when I switch on my LED source ?