I would appreciate any help. The question may seem similar to the question asked at this link: Help me calculate spectral irradiance of an LED from a LED spec sheet , but the answer was never given or posted.
So here is my questions:
I am building a device that illuminates the human eye from a distance of approximately 120mm, with an array of 40 IR LEDs for around 7 seconds. The purpose of this is beyond the scope of the question.
In order to have theoretical evidence that the IR LED's will not cause any hazardous harm to the eye, the total Infrared Radiation exposure should satisfy the limits of the IEC62471 standard. I have posted an image/snippet from the standard of the equation that I need to use below:
My problem is that I do not know how to calculate the spectral irradiance of the IR LED from its datasheet.
The parameters of my setup are the following (Some values retrieved from the datasheet):
IR LED wavelength: 950 nm
IR Centroid wavelength: 940 nm
Number of LEDs: 40
Shape of array: A square of 30 x 30 mm that is positioned in between both eyes (at a distance of 120 mm)
Typical Radiant Intensity per LED: 11 mW/sr
Spectral bandwidth at 50% (∆λ): 42 nm (I am unsure if this is what is needed in the equation)
Distance from eye: approximately 120 mm
Duration of Illumination 7 seconds
Half angle: 60°
Total radiant flux: 35 mW
The units for spectral irradiance is W⋅m^-2⋅nm^-1. Therefore, if I am correct, I can get the W/m² by saying:
- 11 mW/sr*40(Num of IR LEDS) = 440 mW/sr
- W/sr/m² = 0.44/sr/(0.12²) = 30.55 W/m² = 30.55 W.m^-2
However, that's where I get stuck. Therefore, I would like to know the following:
- Am I on the right path?
- If so, how do I convert W/m² to W/m²/nm (W.m^-2.nm^-1) ?
Thank you for the help