How to use regular diode as a photo-element?

There are special diodes, transistors and resistors designed to measure light intensity, sometimes even a regular LED is also used for this task, can be used. I was wondering, if any diode (in a package that doesn't block light rays) could be used? Today I will share the results of my experiments.

Let's start from theory, it's well described on Wikipedia: "A photodiode is a PN junction or PIN structure. When a photon of sufficient energy strikes the diode, it excites an electron, thereby creating a free electron (and a positively charged electron hole). This mechanism is also known as the photoelectric effect. [...] Since transistors and ICs are made of semiconductors, and contain P-N junctions, almost every active component is potentially a photodiode." [source]

P-N junction needs to be exposed to light, so as mentioned we will need diodes in glass bulb. Popular 1n148 diode can be used in this experiment. Below are presented pictures of other diodes that could be used, those pictures were captured by Shoorick, thanks!.

glass diode glass diode glass diode

This signal, so I used an operation amplifier (in non-inverting configuration). Below circuit (after modification of values of resistors, mainly R1) can be used with LEDs, photo-diodes and photo-resistors.

circuit diagram with regular diode used as a photo-element

Below you can see that it works, these two pictures were taken with the same camera settings, first one is darker, you can see the measurement on the multimeter, second one was lighter by an additional lamp, you can see that measurements were different as expected.

complete circuit with a regular diode used as a photo-element complete circuit with a regular diode used as a photo-element

To verify that it's not a EMF noise from the lamp, I placed an object to hide sensor from the light, but it's not metallic, so if it would be the noise that makes the reading increased, the reading should be still high. It isn't, so it's working OK.

complete circuit with a regular diode used as a photo-element

I've also made a version with op-amp replaced by two bipolar transistors in Darlington configuration, it also worked.

a complete circuit with a regular diode used as a photo-element, bipolar transistor used as amplifier

It was quite interesting experiment. If you have ideas about it, please share them!


  1. The best of diodes for this purpose is lowest one, which has crystal open to light. Diodes above have crystals mostly obscured by tightly connected outlets or metalization. I do not know if such "handy" diodes are still in production, anyway they still can be extracted from quiet old hardware ;)

  2. Use a transparent LED, it's more sensitive than a glass diode.

  3. @nimeni, I already mentioned in post, that LEDs may be used :)