# Optics: How would you determine wavelength?

• Aaron Van Rossum
In summary, the conversation discussed the effects of blue light on a red object and how it differs from white light. It was mentioned that the object would appear black if only exposed to blue light, while the reflection coefficient for blue light is lower than red light. It was also noted that determining the color of an object based on reflectivity at one wavelength may not be accurate, as it depends on the overall spectrum of reflectivity. The conversation concluded with the acknowledgement of the need for a different approach in determining the object's color.
Aaron Van Rossum
If there is an light source that is emitting light with the wl of 450nm (blue) and it illuminated a low reflective red object. How would the wavelength be different then if the object was a white object or the emitted light is from a white led. How would we determine this. I am working on a project that shoots light at a certain wavelength at an object and determine its color through a sensor.

For the first situation (blue light on red object), if there is only blue light on the red object, the object should appear black and not reflect anything, this is because the object would simply absorb all wavelengths of light which are not red. If the object is white, then I think you should be able to predict that. Similarly, you should be able to predict what would happen with a white led.

If you object is just a common reflector (no fluorescence), what you send is what you get. The reflected light has the same wavelength as the incoming light.
For the red object the reflection coefficient of blue light is much lower than that of red light. This is why we call it red.
But the wavelength is the same. I don't see how you could determine the color of an object by just measuring reflectivity at one single wavelength. Our notion "color of the object" depends on the whole spectrum of the reflectivity. And even if you know that, you can still have an object that looks blue to you and green to your wife (for example). Even though the spectral distribution of reflectivity does not change.

davenn
Ah ok now I understand. I’m going to have to take a different approach to this. Thanks!

## 1. What is the relationship between wavelength and frequency?

The wavelength and frequency of a light wave are inversely proportional. This means that as the wavelength increases, the frequency decreases, and vice versa.

## 2. How do you measure the wavelength of light?

The wavelength of light can be measured using a spectrometer, which separates light into its different wavelengths. Alternatively, it can also be calculated using the equation: wavelength = speed of light / frequency.

## 3. How does the color of light correspond to its wavelength?

The color of light is determined by its wavelength. Red light has the longest wavelength and violet light has the shortest wavelength. All other colors of the visible spectrum fall in between these two wavelengths.

## 4. What are some real-world applications of determining wavelength?

Determining the wavelength of light is useful in a variety of fields such as astronomy, telecommunications, and medicine. It is used to study the properties of stars, to transmit information through fiber optic cables, and to diagnose medical conditions.

## 5. Can wavelength be changed or manipulated?

Yes, the wavelength of light can be changed or manipulated. This can be done by passing light through different materials, such as a prism, or by using optical devices like lenses and filters.

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