Fast Response Light Sensing with Photodiodes: Building a DIY Radiometer!

RE: Fast Response Light Sensing with Photodiodes: Building a DIY Radiometer!

stanley1O1 — Mon, 09 Mar 2026 00:52:00 GMT

[mention:b0bc65b9ecdc4307bd967592f00e340a:e9ed411860ed4f2ba0265705b8793d05] I was hoping to build the S5973 version. Also, what program did you use for visualizing the data? I was hoping to use it to test lost frames and timing of stimuli in experiments I conduct.

RE: Fast Response Light Sensing with Photodiodes: Building a DIY Radiometer!

JApetWophy — Wed, 16 Jul 2025 17:03:26 GMT

Good day sir !! I'm physics student and I'm conducting a z pinch experiment considering the set up you provide on your sensor can this be use to detect light pulse down to nanoseconds? I would like to build this for my research

RE: Fast Response Light Sensing with Photodiodes: Building a DIY Radiometer!

koudelad — Tue, 22 Oct 2024 18:31:36 GMT

Interesting project, this might be a cheap way to verify if our electronic devices use PWM or other driven back-light.

I have one suggestion - it would be great if any type of rechargeable batteries could be used. I have never seen 1/2 AA in my life and not sure if it is possible to buy it around here. Of course, it could be replaced by 8 LR44 batteries glued together using some tape, but this is imho an ecological disaster :)

RE: Fast Response Light Sensing with Photodiodes: Building a DIY Radiometer!

DAB — Thu, 17 Oct 2024 19:38:51 GMT

Great project.

I have not used a radiometer since I worked in a laser lab back in the early 1970's.

RE: Fast Response Light Sensing with Photodiodes: Building a DIY Radiometer!

genebren — Thu, 17 Oct 2024 14:59:42 GMT

Here is my radiometer. This little guy has had a spot near the window for over 30 years. On a bright day, in direct sunlight this thing will really spin.

RE: Fast Response Light Sensing with Photodiodes: Building a DIY Radiometer!

shabaz — Wed, 16 Oct 2024 19:12:56 GMT

Just another quick experiment..

I tried a camera flash (i.e. xenon tube). Then I held a cheap AliExpress neutral density filter (ND4) over the flash, and reattempted.

As I understand (I'm no photographer), the ND4 should only provide a quarter of the light power. However, I'm seeing a ratio of about 0.4. I don't know the explanation for that. Maybe these filters are just not that accurate. (or maybe the filter only works for the visible range, and maybe the xenon tube emits some content beyond that. No idea. Just speculating!).

RE: Fast Response Light Sensing with Photodiodes: Building a DIY Radiometer!

genebren — Wed, 16 Oct 2024 16:08:04 GMT

Great project! I really like the packaging and the simple, but well thought out approach is very inspiring.

I played around with some photodiodes for some of my indoor lighting projects. I had hoped to be able to sense differences between sunlight and overhead lighting, in an effort to have my task lighting to switch on whenever the overhead lighting was on. Poor choices of photodiode and sensor placement made the sensor far less sensitive than I had hoped for. I may have to re-visit this project soon.

Thanks for sharing!

RE: Fast Response Light Sensing with Photodiodes: Building a DIY Radiometer!

jc2048 — Wed, 16 Oct 2024 09:48:49 GMT

Nice project. Being able to measure light and view waveforms, with such a simple circuit build. I think you might find a good few people trying this.

Are you sure the SFH203 would be slower? It's a small-area device, with about 5pF of reverse capacitance at -12V, and rise and fall times less than 5ns. Where it falls down would be lower sensitivity, making the radiometric side more difficult.

The phosphor lag you see is a problem when controlling white LEDs with PWM, particularly if you try to mix warm and cool LEDs to give variable colour temperature. The base LED is high-intensity blue, so a lot of the blue part of the spectrum is simply light that punches through the phosphor, but of course that portion disappears straight away, leaving the red and green light down-converted by the phosphor to decay more gradually.

RE: Fast Response Light Sensing with Photodiodes: Building a DIY Radiometer!

michaelkellett — Wed, 16 Oct 2024 09:33:17 GMT

Interesting box Shabaz.

Hamamatsu make some very nice optical parts.

I've done a lot of work over the last 12 years with NIR LEDs and PDs for measuring CO2 concentrations - but we don't pulse as fast as 30MHz - only up to maybe 10kHz rate and down to 20us wide pulses.

I like your label.

I've been looking for a source of thin polycarbonate to reverse print with an ink jet printer but although it is made I can't find anyone selling A4 sheets - and a 1m wide roll is expensive and impossible to handle.