OPT3001: OPT3001 evening offsets

Hi Sean,

Apologies for the delay in response.

What are you using as the calibrated device? What is the spectral response of the Everlight device and the calibrated device? Do they closely match the response of the human eye? It could just be that the OPT3001 is more sensitive to certain wavelengths of light compared to those other two devices.

Another thing that might be good to check is whether the enclosure is having any sort of effect on the response of the sensor. If you take it out of the enclosure, how does it compare to the other two devices?

Thanks,

Daniel

Hi Daniel,

We are currently using two Megatron DL5 units, both calibrated against CIE Illuminant A (2856 K). The device aligns well with the human photopic response curve V(λ), and both units are providing consistent and comparable results.

Using these DL5s as references, we successfully calibrated our Everlight sensor, and the readings have been stable and repeatable.

However, when we test with the OPT3001, we observe significantly different readings in the evening, even after trying multiple enclosures and sensor orientations. The results remain consistently offset compared to the Megatron DL5 reference.

Given that our Megatron DL5 units are somewhat older, we are wondering whether this discrepancy could be related to differences in:

• The OPT3001’s spectral response vs. standard V(λ),

• The age or drift of our reference equipment,(Even tho its calibrated)

• Or perhaps the OPT3001’s calibration assumptions under varying lighting conditions (incandescent vs. daylight).

Could you please clarify how closely the OPT3001’s internal photodiode response matches the standard CIE photopic curve (V(λ))? And are there recommended calibration methods for aligning the OPT3001 with reference instruments calibrated against Illuminant A?

Any guidance on reducing these discrepancies would be greatly appreciated.

Sean

Hi Sean, 

Device response plot included in data sheet is taken at TA = 25°C, VDD = 3.3 V, 800-ms conversion time (CT = 1), automatic full-scale range (RN[3:0] = 1100b), white LED, and normal-angle incidence of light: 

Your results do seem odd. The strong IR rejection of OPT3001 could contribute to this since there is greater proportions of IR at sunset, However I would not expect the differences to be as large from that effect. 

Are there any positional or orientation differences between the OPT3001 and the everlight sensor within your system?

Has this been seen across multiple devices or one single OPT3001?

Could you please give me a walk through of your calibration procedure?

Thank you, 

Joseph Scherphorn 

Hi Joseph,

We have tested multiple orientations and fields of view, but the inconsistencies persist.

We have also tried using different devices, yet the results remain inconsistent.

We have not yet performed any calibration on the sensor and are currently relying on the raw lux values. However, based on the results, I don’t believe implementing a lookup table alone will resolve the discrepancies between the two.

From my research, our calibrated devices all comply with the BS 667 standard. Is the OPT3001 based on a different standard, such as DIN 5032-7? If so, this difference in standards could explain the discrepancies we are observing?

Sean

Hi Sean, 

I've reached out to team who handles certs to understand how we align with these standatrds. 

You say device is being used with 800ms conversion time.  What are the other settings of the configuration register ? specifically what range is being used?

I agree with Dan that it would be good to see devices performance without enclosure. Are spectral transmission properties of cover glass known ?