# A few general questions about Optics

• ShaggyKyle
In summary, white light has less intensity than blue light because of the phosphor coating on the inside of blue LED's. If you want to combine different colors of light, you need a lens to focus them onto a white sheet of paper.
ShaggyKyle
Does light intensity change along with frequency? In other words, if you put the same voltage behind a white LED light and a blue LED light will the white light have a higher intensity or just a different frequency?

Also, would shining a white light through a very clean thin colored filter change the intensity?

Lastly, what would be required to converge different colored lights together? Do I just need a lens, or do I need a prism of some kind?

If you have any links to where I can find out information like this, I would be most appreciative. I tried Google but nothing I found answered my questions. Until I get a book on optics, my thanks to whoever can help answer my questions.

ShaggyKyle said:
Does light intensity change along with frequency? In other words, if you put the same voltage behind a white LED light and a blue LED light will the white light have a higher intensity or just a different frequency?

Also, would shining a white light through a very clean thin colored filter change the intensity?

Lastly, what would be required to converge different colored lights together? Do I just need a lens, or do I need a prism of some kind?

If you have any links to where I can find out information like this, I would be most appreciative. I tried Google but nothing I found answered my questions. Until I get a book on optics, my thanks to whoever can help answer my questions.

A white LED is a blue LED--a blue LED with a phosphor coating on the inside! Yep, the same kind of phosphor that coats the inside of a flourescent light. For this reason, the white LED will radiate fewer photons than the blue LED, as the phosphor in the white LED is somewhat lossy.
If you were to compare a blue LED with a red LED (neither have phosphors in them), then yes, the blue led will radiate less light with the same current draw, because blue is a more energetic source of electromagnetic radiation.

Shining white light thru a color filter will pass only that frequency that the color filter will not absorb. So while the passed frequency will not be decreased (just pretend we're using an ideal filter), all other frequencies get absorbed by the filter, thus the frequencies that get absorbed will be radically attenuated and lessened.

If you're "converging" incoherent light (the kind of light coming from your LED, or a flourescent lamp), then using a lens to focus the different colors onto a white sheet of paper will very effectively blend them.

One last thing I'll leave you with: research the Fabray/Perot interference/color filter. These filters have an extremely narrow bandwidth, and learning how these color filters work will give you a great lesson on color, light and interference in general.

Thank you very much for the quick informative reply. You answered everything I asked and the questions I didn't think about asking!

ShaggyKyle said:
Thank you very much for the quick informative reply. You answered everything I asked and the questions I didn't think about asking!

You're welcome. Now vote me in as Forum Science Advisor.

## 1. What is optics?

Optics is the branch of physics that deals with the study of light and its properties, including how it interacts with matter and how it is perceived by the human eye.

## 2. What are some applications of optics?

Optics has a wide range of applications, including in telecommunications, photography, microscopy, astronomy, and laser technology. It is also used in industries such as medicine, defense, and manufacturing.

## 3. How does light travel?

Light travels in a straight line at a constant speed of approximately 299,792,458 meters per second in a vacuum. It can also travel through different media, such as air, water, and glass, but its speed and direction may change.

## 4. What are the different types of lenses?

There are two main types of lenses: convex lenses (also known as converging lenses) and concave lenses (also known as diverging lenses). Convex lenses bend light rays towards a focal point, while concave lenses bend light rays away from a focal point.

## 5. How does the human eye work in relation to optics?

The human eye is a complex optical system that works by focusing light onto the retina, which contains photoreceptor cells that convert light into electrical signals. These signals are then sent to the brain, where they are interpreted as images. The lens of the eye acts as a convex lens to refract light, and the muscles in the eye adjust its shape to focus on objects at different distances.

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