# Focus or parallelize the light from an LED

• Lexinas
In summary, the speaker is looking to bring a LED, 620nm, with a viewing angle of 20°, in a distance of about 20cm on a lens with as many photons as possible. They suggest positioning a converging lens at the distance of the focal length to the LED, in order to get as many photons as possible into the lens. They also mention using a compound arrangement with two lenses to achieve this goal, and suggest looking into second hand SLR camera lenses on eBay. The speaker advises doing some sketches using the formula 1/f = 1/u + 1/v to determine the best solution based on the lenses available.
Lexinas
Hello, everyone,

I have a LED, 620nm, with a viewing angle of 20°. I would like to bring this light in a distance of about 20cm on a lens with as many photons as possible.
My idea is to position a converging lens between the LED and the lens. To be exact, I would position the lens at the distance of the focal length to the LED. To get as many photons as possible into the lens, the lens should be as close as possible to the LED so that as much light as possible goes through the lens and that would correspond to a very short focal length.

Are my considerations correct so far?

Best regards
Lexinas

Yes, that's right. The closer, stronger, and larger the lens, the more light that you can intercept with it and redirect onto the 2nd lens.

A compound arrangement with two lenses could do what you want without needing a single large diameter, lens.

eBay has a selection of many different second hand SLR camera lenses you could play with and the cheapest lenses are only a few quid each. (Even the lowest spec lenses are actually pretty good.)
I do appreciate that you are not planning on building a whole Optics lab but you could find it interesting and get a result.

Do some sketches , using the dreaded 1/f = 1/u + 1/v formula. The first lens will form one virtual image behind the LED and the second lens could focus that intermediate image to a point where you want it. There are a host of possible solutions, depending on the lenses you can get hold of.

## 1. How do you focus the light from an LED?

To focus the light from an LED, you can use a lens or a reflector. The lens can be convex or concave and should be placed in front of the LED to focus the light in a specific direction. The reflector can also be used to direct the light from the LED in a particular direction.

## 2. Can the focus of an LED be adjusted?

Yes, the focus of an LED can be adjusted by changing the distance between the LED and the lens or reflector. Moving the lens or reflector closer to the LED will result in a narrower focus, while moving it farther away will result in a wider focus.

## 3. What is the purpose of focusing the light from an LED?

The purpose of focusing the light from an LED is to control the direction and intensity of the light. By focusing the light, you can make it more concentrated and directed, which can be useful for specific applications such as spotlights or laser pointers.

## 4. How does parallelizing the light from an LED differ from focusing it?

Parallelizing the light from an LED means directing the light in a parallel beam instead of focusing it in a specific direction. This can be achieved by using a collimator, which is a lens that creates a parallel beam of light. Parallelizing the light is useful for applications such as fiber optics and optical communication.

## 5. Can the light from an LED be both focused and parallelized?

Yes, it is possible to both focus and parallelize the light from an LED. This can be achieved by using a combination of lenses and reflectors to first focus the light and then use a collimator to parallelize it. This technique is often used in advanced optical systems and devices.

• Optics
Replies
10
Views
2K
• Optics
Replies
1
Views
1K
• Optics
Replies
10
Views
912
• Optics
Replies
13
Views
927
• Optics
Replies
10
Views
3K
• Optics
Replies
2
Views
2K
• Optics
Replies
17
Views
1K
• Optics
Replies
2
Views
978
• Optics
Replies
58
Views
5K
• Optics
Replies
41
Views
457