Alan Phelps

Flashlights, Searchlights and Car Headlights
Car headlights use concave lenses on their light sources to optimize light in the dark and so the driver can see a larger part of the road while driving at night.

Flash lights, searchlights and car headlights have been around for an extremely long time and serve a useful role in our society but just how do they work? They each use various lenses to either focus the light onto one specific target, to magnify the rays while keeping them parallel or spread it out to cover a larger surface area. They each take advantage of optical technology to optimize the brightness of the light source and to ensure that they continue to provide a use to society.

A searchlight is used to signal the caped crusader in the 2008 film, "The Dark Knight"


1.0 Flashlights
- 1.1 Convex Lenses
- 1.2 Concave Lenses
2.0 Searchlights
3.0 Car Headlights
4.0 Video
5.0 References

1.0 Flashlights
A flashlight using a converging lens to focus light onto one specific area.

A flashlight using a diverging lens is spreading the light out onto a larger surface area.

Just like most useful inventions in everyday society, the inner workings of a flashlight are actually very simple. Flashlights utilize various lenses to optimize light and to either focus it in one place or spread it out along a larger area. Flashlights are able to focus all their light on one place by using a convex lens and are able to make the light source appear larger by using a concave lens. convex lensed flashlights are used for examination of smaller objects while concave lensed flashlights are used for more when you need to light up a room during a power outage. Without the use of lenses, flashlights would give out very small amounts of light and would be virtually useless.

1.1 Convex Lenses
This ray diagram shows how light goes through a convex lens. it begins parallel but when it hits the lens, the light converges toward the focal point.

If you ever need a flashlight so you can focus in on a certain object to study it closely in the dark, you are going to need one with a convex lens. Convex lenses curve toward the light source so the light is redirected or converged to focus on a specific area or principle focus. Convex lenses do just the same as a magnifying glass would for a ten year old trying to burn ants as it does for a flashlight, it concentrates the light onto one place to make the light brighter and hotter. If you want to light up a darkened room then this is not the flashlight for you. You need a concave lensed flashlight.

- very usefull when looking at small opjects up close
- maximizes the brightness and heat given off by the light source
- limited usage
-light only shines on a very small area.

Flashlight Ray Diagram

1.2 Concave Lenss

This is a ray diagram showing light passing through a concave lens

In flashlights, concave lenses are used to spread out light to cover more space. A concave lens curves away from the light source so the light rays given off by the bulb diverge outwards and cover a larger area. In the diagram to the right you can see that the rays split apart as soon as the hit the lens causing the light to appear less bright. A concave lensed flashlight is the exact opposite of a convex one. They both have their disadvantages and their perks

- Able to maximize the area the light covers
- the brightness of the light is lowered since it is so out

Flashlight With Concave Lens

Two searchlights crossing beams

2.0 Searchlights

Searchlights are much more unique than flashlights. They use both mirrors and lenses to create a giant beam of light. looking at the diagram below we see the inner workings of the searchlight. A light source (which acts as a focal point) sends light rays to a concave mirror at an angle. The rays then get reflected parallel to the principle axis go out into the sky through a flat lens. This causes all of the light rays to be parallel to each other while shining up into the sky to create the image of a single large beam of light.

3.0 Car Headlights
A round car headlamp.

Car Headlights are extremely important to the safety of our drivers and they are probably the most intricate out of all three (flashlights, searchlights & headlights). They utilize concave lenses and even reflective mirrors. If you take a look at the diagram to your right you see the inside of a car headlight. Headlights work by the light source shining rays to the reflective mirror acting like a focal point. The mirrors magnify the light and send the parallel rays into a concave lens which separates the rays and spreads the light out along the road in front of the car.


4.0 Video
A video showing the effects of light on various lenses.

5.0 References

Optical Lens - YouTube . (n.d.).YouTube - Broadcast Yourself. . Retrieved May 27, 2012, from

Headlamp - Wikipedia, the free encyclopedia. (n.d.). Wikipedia, the free encyclopedia. Retrieved May 27, 2012, from

Lens (optics) - Wikipedia, the free encyclopedia. (n.d.). Wikipedia, the free encyclopedia. Retrieved May 27, 2012, from

Searchlight - Wikipedia, the free encyclopedia. (n.d.). Wikipedia, the free encyclopedia. Retrieved May 27, 2012, from

The Convex Lens. (n.d.). Welcome to Play-Hookey!. Retrieved May 27, 2012, from