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OPT3002: PAR Meters For LED Grow Lights

Part Number: OPT3002
Other Parts Discussed in Thread: OPT3001

Dear team,

I have a customer which has a requirement to build PAR meter, I do have a few questions: 

1. can you please advise if TI has any reference design/APP NOTE about PAR meter?

2. can you please advise if our OPT3002 can be suitable for such a design and if there is any way to separate wavelengths (colors) by a mechanical (non-optical) filter?

Thanks and regards,

Shai

  • Hi Shai,

    I don't see a reference design or app note for a PAR meter.

    OPT3002 will give a single value and does not provide a way to separate wavelength. If you were able to place a filter that only exposed the sensor to a single wavelength at a time then you could do this, but the wavelength filtering would have to be done externally. What do you mean by mechanical (non-optical) filter?

    Could you provide some detail on what you are trying to measure with OPT3002? Are you trying to measure specific wavelengths or an overall power level?

    Best,

    Alex

  • Hi Alex,

    Bascily PAR measures Photosynthetically Active Radiation (PAR, in µmol of photons m-2 s-1) very popular in greenhouses application.

    Plants use light in the wavelength range from about 400 to 700 nm to drive photosynthesis.

    The efficiency with which plants use light varies somewhat across this range so it is important to split and measure specific wavelengths by using multiple OPT3002 devices per the desired wavelengths. see pic below:

    the common way to separate wavelengths is by prism but I have read in the below E2E thread that was mentioned color-filters can you please elaborate more about this?

    https://e2e.ti.com/support/sensor/optical_sensors/f/989/p/415886/1479334?tisearch=e2e-quicksearch&keymatch=rgb%20opt3001#1479334

    Thanks in advance.

    Regards, 

    Shai

  • Hi Shai,

    Thanks for the details. Firstly, I'd like to note that I am not an expert on light filters and the below information is theoretical to give you an idea of how an OPT device could function given that you are able to get a filter that blocks all wavelengths except for a single one. In practice I do not believe it is possible to get such a filter and the best would be a sort of narrow band-pass optical filter, but you would have to check into this. The below idea will still work, but since you are letting in a range of wavelengths instead of a single one the OPT would give a value for that range instead of each wavelength.

    OPT3001 (or OPT3002 for that matter) will give you a single value that corresponds to the device response to the sum of all wavelengths of light exposed to the sensor. If you have an OPT300x device and place a filter that only allows the wavelength of interest you can ensure the OPT only gets exposed to that wavelength. Since the device response across wavelength is in the datasheet you can normalize the response to account for the device attenuation at the given wavelength. For your application you would need multiple filters, one filter per wavelength of interest. So if you need n wavelengths you would either need n number of OPT devices each with a different filter or n filters and a way to switch the filters.

    You will have to check if this is something that can mechanically and optically be done in your system.

    Best,

    Alex