FIR or Far InfraRed is (>5um) but I'm not sure of the peak wavelength.

We also generate IR as heat, but this is a longer wavelength than most IR LEDs and PD's can detect. ( plastic is higher than glass so they can use thinner lenses for eye-frames)īut skin is also an irregular surface compare to the wavelength, so it also scatters light. It also conducts IR so it is semi-transparent, which is good for finger sense heart rate and oximeters.īut since the dielectric constant at this wavelength is greater than 1 it also refracts. Skin reflects some IR, even if you are black-skinned. The detector must have a black lens which passes IR and blocks stray visible light. The circuit I built is going to be used to detect when a finger or hand gets closer to the sensor. So then what's the point of having an IR LED in the circuit if the circuit already activates when a finger gets closer to the circuit, or am I understanding this wrong? Provided the threshold voltage is low enough. The second part I noticed is that even if the IR LED is removed the sensor still activates because our bodies do also emit radiation which the photodiode can detect. So which is correct does the IR light emitted by the IR LED gets reflected or refracted towards the photodiode when your finger or hand moves closer to the sensor? But other sources say that the human body does not reflect IR light but rather refracts it. My question is, I have read some sites that state that your human body reflects IR light transmitted by the IR LED hence when you touch or move your hand close to the proximity sensor the circuit will activate. I am currently working on a project that uses an IR LED and a photodiode in a proximity sensor configuration (shown below).

Sensor infrared proteus