Wavelength and resistance of an LDR

In summary, Light Dependent Resistors have a spectral response, meaning they have a higher response at certain wavelengths of light compared to others. This can cause a problem when trying to measure the change in light intensity from a singular light source. To compensate for this, one could use LDRs with a uniform spectral response or use data on the LDR to correct readings for different wavelengths. Monochromatic and neutral density filters can also be helpful in this task.
  • #1
Deleted member 74205

Homework Statement



Light Dependent Resistors appear to have a spectral response; that is, at different wavelengths of light, the LDR will become less resistant than at others. For example, a cadmium sulphide LDR has a high response at 550 as shown at http://www.biltek.tubitak.gov.tr/gelisim/elektronik/dosyalar/25/LDR_NSL19_M51.pdf on page 2. This may adjust the response to light at a singe given light intensity.
I am trying to measure the change in light intensity from a singular light source as it varies with wavelength, so as you can imagine the above factor causes me a problem. Is/are there either a) a kind of LDR that as a completely uniform "spectral response" or b) other kinds of resistors which have different spectral responses that could be used to compensate for this one or c) another way of compensating for the problem?

Homework Equations



Not Applicable

The Attempt at a Solution


Other kinds of LDR which have the same response at different wavelengths
an LDR with a uniform spectral response
some kind of scale which adjusts for the problem
 
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  • #2
I think you have to use the data on the LDR to correct your readings for different wavelengths. You are given the relationship between resistance and Lumens, so that is a simple calculation. Then to correct for wavelength, divide the calculated intensity by the percentage response for that wavelength.
 
  • #3
I think this is reasoable; what I'm confused is whether your light source has a spectral shift versus intensity and that's part of the problem. Maybe if I had a bigger picture of what you're trying to do here, could be of more help. When i worked with light as a grad student, monochromatic filters and neutral density filters were essential tools of the trade.
 
  • #4
Thanks Mentz114, that was really helpful, and I think may have fixed my problem. :D

Just for completeness, in response to denverdoc, the light source has many wavelengths, the task is to find the intensity of each individual wavelength.
 

1. What is an LDR?

An LDR, or Light Dependent Resistor, is a type of electrical component that changes its resistance depending on the amount of light that falls on it. It is a type of photoresistor, which is a type of resistor that changes its resistance based on the intensity of light.

2. How does the wavelength of light affect the resistance of an LDR?

The wavelength of light does not directly affect the resistance of an LDR. However, the intensity of light, which is related to its wavelength, does affect the resistance. Generally, the higher the intensity of light, the lower the resistance of the LDR.

3. What is the relationship between the resistance of an LDR and its sensitivity to light?

The sensitivity of an LDR to light is directly proportional to its resistance. This means that the higher the resistance of the LDR, the more sensitive it is to changes in light intensity. Conversely, a lower resistance LDR will be less sensitive to changes in light intensity.

4. Can the resistance of an LDR be controlled?

Yes, the resistance of an LDR can be controlled through external factors such as light intensity or temperature. By adjusting these factors, the resistance of the LDR can be manipulated to achieve a desired level.

5. What are some practical applications of LDRs?

LDRs are commonly used in automatic lighting systems, such as streetlights, where they detect changes in light intensity and turn on or off accordingly. They are also used in cameras to control the amount of light that enters the lens, and in solar panels to measure the amount of sunlight for optimal energy production.

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