I want to add the lux meter to my application. My controller works with 3.3V and ADC max reading voltage is 1.2Vref. I tried with LDR but I'm not able to get accurate values and the values also not useful for calibrating.

Are there any other possibilities to get lux meter with my controller? I used below circuit I used this circuit.

It gives max 1.1V and min 0.4V with Light changes enter image description here

  • \$\begingroup\$ adafruit.com/product/1246 \$\endgroup\$ – MaNyYaCk Jul 17 '18 at 8:31
  • \$\begingroup\$ you'll bet better results with the right amplifier between the sensor and the microcontroller. \$\endgroup\$ – Jasen Jul 17 '18 at 9:29
  • \$\begingroup\$ use an ambient light sensor that has a calibrated digital (often I2C) interface. \$\endgroup\$ – Wouter van Ooijen Jul 17 '18 at 9:38

Your question, "Which one is better" does have an answer, but first we need to look at the rest of your statements.

I'm not able to get accurate values and the values also not useful for calibrating.

You should realize that for many years (more than 50) LDRs, typically CdS, have been used in light meters, and are still used today, although their use has declined radically. So your inability to produce a useful result says everything about your skill level and nothing about the utility of LDRs.

With that said, CdS has an intrinsic advantage over silicon - its color response is close to that of the human eye. Silicon photodiodes typically have a lot of response in the IR, so they need a pretty good filter to shape their response curve to match what we see.

On the other hand, silicon tends to be easier to use, and more sensitive as well.

As for alternatives, sure. Bolometers are extremely sensitive. But if you can't get good results with an LDR you will never, ever make a bolometer work.

You need to do more research in how to amplify an LDR's output.

To answer your question, photodiodes are easier to interface and are faster. You can even make a light meter using just a PD and a resistor, which will give extremely linear results. This is not necessarily a good thing, since "normal" light levels will typically cover at least a 1000:1 range, which complicates the issue significantly.

  • \$\begingroup\$ If you see my question clearly, I mentioned that my controller ADC Vref value as 1.2V and it's work with 3.3V. So I can't use one single LDR with resistor or single Photo Diode with resistor. I tried with one circuit which produces max 1.1V and min 0.4V. With wide range of Lux and small range voltage, can't get one equation. \$\endgroup\$ – ravi teja Jul 19 '18 at 7:23
  • \$\begingroup\$ @raviteja - Your voltages are irrelevant. LDRs and photodiodes will work over almost any range (as long as it isn't too great). And sure, you can use a single resistor - if your measurement range is small enough. You didn't specify it, though. Since you seem to think the voltages matter, my statement "You need to do more research in how to amplify an LDR's output." stands. \$\endgroup\$ – WhatRoughBeast Jul 19 '18 at 13:47

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