Flashlight Design

For our first independent project, we were tasked with designing a lantern. We were given an LED lightbulb, a 9V battery, and a fixed carbon resistor - it was our responsibility to find the remaining materials. Our lanterns had to be: functional, aesthetically pleasing, and creatively use materials, while maximizing light. Though I initially imagined crafting a cute paper lantern, this idea was quickly discarded when I realized how teeny my single LED bulb was. I decided that a flashlight would be the best device to maximize the light output of a single bulb.

Though most design processes begin with a sketch, I began with scavenging around the Sustainability Cooperative in which I live for some materials that I could craft into a flashlight. I found a glue bottle to use as the housing, a small terra cotta pot to use as the concave device that would - lined with aluminum foil as a reflector - channel light from the LED into a concentrated beam. For wires, I found some old thick speaker wires which I stripped down and extracted a few copper wires. 

This is the sketch of my flashlight, with a diagram of my circuit:

List of all materials used:

1 9V battery

1 3.2 V LED lightbulb

1 266 Ω resistor

1 Aleene's Tacky Glue bottle, with neck cut off

1 small terra cotta pot

1 piece aluminum foil

4 copper wires (taken from speaker wires)

2 brass fasteners

1 small paper clip

electric tape

paint, for decoration

A resistor is a necessary part of the circuit which provides resistance to limit the flow of the electric current coming from the battery so that a lightbulb with a voltage lower than the battery doesn't "blow out."Though a resistor was provided, I had to choose the resistance value that I needed for my circuit. I calculated that I needed a 290Ω resistor using Ohm's law: V = IR, where V is voltage, I is current, and R is resistance. The closest resistor to 290Ω that I had access to was a 266Ω.

My calculation:

9V battery - 3.2 V LED = 5.8 V

5.8 V = 20 mA*R

5.8V/20mA = R

0.29 kΩ = R

290Ω = R

Building the flashlight was a bit of a challenge, but it was also pretty fun. Before construction, I assembled my circuit, without housing, to make sure it worked.

 I first built the cone for the lightbulb by putting the tin foil into the pot and wrapping it around the lip to create a reflective concave surface. I poked a hole through the center of the foil and stuck the lightbulb through. I connected one of these wires to the resistor, and then connected the resistor to the negative terminal of the battery with another wire. I attached a wire to the positive terminal of the battery. Since I don't know how to solder (yet), I attached of my wires to the battery and bulb with tape.

Stripping the audio cable to get wire

Attaching the wire to the bulb

To make the switch, I made two holes in the side of the glue container and poked the brass fasteners in. I shortened the prongs on the fasteners beforehand to make sure that the prongs from the two fasteners wouldn't touch inside the tube (thereby ruining the circuit break). Now it was time to connect the wires, but then I realized that I couldn't fit my hand far enough into the tube, so I removed the fasteners and poked the remaining battery wire and the wire connected to the LED through the holes and wrapped them around the pins, which I stuck in. I wrapped one end of a paper clip around one of the fasteners - if the other end of the paper clip is looped around the other fastener, the circuit will be complete, and the light will turn on. Finally, I taped the battery down to the bottom of the tube so that it wouldn't jiggle around. To complete my flashlight, I fed the two wires from the resistor and the switch through the pot and connected them to both prongs on the LED, and glued the pot into the glue tube.

Designing and constructing the flashlight was easier than I anticipated. However, I made a couple mistakes. When I finished building and turned on the switch, lo and behold!...my bulb didn't light up. This was very frustrating, and I had to problem shoot. It turns out that I had connected the wire attached to positive terminal of the battery to the negative leg of the LED instead of the positive leg. Also, during this project I wasted a lot of time disconnecting and then reconnecting wires because I didn't spend enough time thinking about the order in which I would assemble different parts of the flashlight. In the future, I will plan out the steps of the building process more before jumping into it.

The finished product in action!

I am proud that, aside from the bulb, resistor and battery, I was able to construct a flashlight using recycled materials. However, one of the limitations of my lantern is that once the battery dies, it will be very difficult to replace it because there is no easy way to access the inside of the housing as the top is glued on. I envision that my flashlight could be easily built by anyone with a few basic craft supplies. Since the light is actually quite bright, the flashlight can function as any store-bought flashlight can. I will keep mine at hand in my room in case Wellesley has any unexpected power outages...