I am currently working on a project which requires the the circuit to perform specific task if a specific colour of laser is detected (something like a basic remote control). Is there a sensor or a way to make LDRs sensitive to only one colour of light.
I tried to find the solution but each time I end up with solutions involving Colour sensor which detects the reflected light from a coloured object not the colour of light.
I am currently working on a project which requires the the circuit to perform specific task if a specific colour of laser is detected (something like a basic remote control). Is there a sensor or a way to make LDRs sensitive to only one colour of light.
While there are many solutions for making spectrally resolved detectors (diffraction gratings, prisms, dielectric filters), the overwhelming most common approach used in remote controls is to put a simple piece of colored glass in front of the sensor. Light not matching the desired color is absorbed.
You might wonder why such simple methods are preferred. The reason is that absorptive filters are very, very cheap and they can be made arbitrarily selective by simply making the glass thicker, which will exponentially increase its absorption. For this reason, even a few cents worth of colored plastic can often be highly effective. If better absorption is required, there are also speciality glasses designed for absorption of specific wavelengths. See for example: https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=999
(note that glasses are available from many vendors, so you can often buy them for a tiny fraction of the list price online)
For applications where two lasers are very close in wavelength (tens of nanometers apart or less) there are also dichroic filters, which can have extremely specific pass bands. However, these are orders of magnitude more expensive, very fragile, and must be kept clean or their selectivity is degraded.
Your title does not match your question.
If you want to determine the colour of the laser, there are photodiodes whose construction consists of two overlapping photodiodes on the same substrate. The photodiodes have different responsivity curves and the result is that if you expose a monochromatic wavelength to it, the outputs of the two photodiodes will be unique and allow you to identify the wavelength. It won't work when also exposed to ambient light though...unless the laser overwhelms ambient light, I suppose.
But if you are only trying to detect a known wavelength then just get an interference (dichroic) filter and stick it over a photodiode. Filters can be expensive though and it could be cheaper to go with the above method (even though those photodiodes are also quite expensive).
If you're trying to detect which of several quite different light sources is on, consider using several general-purpose photodetectors with coloured filters in front. This works well when you have red and green, for example.
You can get very good "colour gel swatches" from theatrical lighting suppliers. Many come in a book with the spectrum printed for each filter. Just experiment with different combinations of colours until you get the selectivity you need.
