Dark Activated Film Canister Night Light

About: The name Cat’s Science Club comes from my daughter Aly, whom I call Aly Cat. She inspired me to take my love of science, and the fun I have with my students, to as many people as I can. Both my daughters hel...

A light that turns on in the dark! Not as hard as it looks. We are beginners and if we could do it you could too.

We liked the mini-mood lighting and the flashlights we made but wanted to try something else. Cool Cat has several film canister flashlights in his room and a mini mood light but he forgets to turn them off. So we came up with an improved night light for him that will go on in the dark and off during the day.

This is different then the mini mood light as it does not have a switch, light sits lower in canister (providing a nicer effect), and the light turns on in the dark and off in light.

The pictures do not do this light justice. They look amazing in the dark.

https://www.instructables.com/id/Dark-Activated-Night-Light/ is what we saw on instructables. Please check it out.
https://www.instructables.com/id/Light-Sensitive-Night-Light/ was mentioned in the comments of the instructable above.

Step 1: Material

3V Coin Battery
100 Ohm Resistor
10K or 20K Resistor
Film Canister - Translucent
Soldering Iron
Tranistor NPN
Wires - 2 About 2 Inches Long
Wire Cutters

Prototype Paper (Circuit Board) for Option 2 Shown with 20K Resistor

Step 2: Circuit Drawing / Board

This is the prototype we used to understand what we were doing as we are beginners with electronics. We drew a schematic that we could understand.

Step 3: Understand Transistors

E is the emitter, B is the base, and C is the collector.

Illustrations taken from http://sunburst.usd.edu/~schieber/psyc770/transistors101.html

Step 4: Connecting and Soldering Option 1


Strip your two wires. Our black wire is negative and the gray is positive (not used in the pictures).

Wrap one end of LDR to the negative wire and collector side of transistor (C).

The other side of the LDR is still free.

Connect one leg of the 10K resistor to both the free leg of the LDR and the base (B) of the transistor.

Connect one leg of 100 Ohm resistor to free end of 10K resistor.

Connect positive leg (longer leg) of LED to the 100 and 10K resistors' connection end.

Connect negative leg of LED (shorter leg) to Emitter (E) of the transistor.

Connect free end of 100 Ohm to positive wire.

Solder all connections as needed.

Step 5: Circuit Board Option


We cut the board in 1/4 then rounded off the edges.

Strip your two wires and solder your positive and negative wires to the board. Our black wire is negative and the gray is positive.

Put LDR through board and solder one end to the negative wire. Cut the extra wire. Wear safety goggles.

Put transistor through board and solder collector (C) to negative wire and the LDR that is connected to the negative wire. The other side of the LDR is still free.

Put 10K resistor through board and solder one leg to both the free leg of the LDR and the base (B) of the transistor.

Put 100 Ohm resistor through board and connect to free end of 10K resistor.

Put LED through board and connect positive leg (longer leg) to the 100 and 10K resistors' connection end.

Connect negative leg of LED (shorter leg) to Emitter (E) of the transistor.

Connect free end of 100 Ohm to positive wire.

Check to see if circuit works by touching the positive wire to the positive side of 3V coin battery.

If light does not light, check connections and refer back to diagram drawn.

Step 6: Add Battery

We taped the back of the circuit board thinking that would help with shorting but it is not needed. The battery is covered with plenty of tape. Also the glue just glued itself to the tape and pulled it off later. Suggest just gluing to bottom of board and taped up battery.

Bend back the wires and cut to length.

Strip wires.

Tape to battery.

Glue battery in place.

 At this point we looked at our first completed board, ever!

Instructable members have given us the courage to go outside our comfort zone! Thank you!!

Step 7: Film Canister

Now you need the film canisters. We added a magnet to one film canister but not the other. You can decide on how you would like yours. We thought the magnet was a better idea then gluing the battery to the bottom of the canister. Easier to get out and change the battery as needed. The only problem is that it sits higher and gives a tiny bit less glow throughout the canister.

Drop circuit gently in canister. Glue in place if desired.

Dim lights and check.

Put lid on.

Step 8: Enjoy!

Dim the lights and enjoy!

Did you notice the two colors together give a purple hue?

Step 9: Problem Solving

First we are beginners so we look for others to help solve problems in a positive and helpful manner. Please and thanks.

Why is the light on even though there is light in the room? Try going to a brighter area.

Why is the light occasionally flashing on and off? Check wire connected to battery. They may come lose as the canister gets shaken around.

Why did this circuit not work? 1. Check connections and refer back to the diagram. 2. Blame us. We really had a hard time explaining this instructable. The circuit board was a challenge for us flipping back and forth.

Where do we find film canisters? We sell them at Cat's Science Club but use anything. Your imagination is a great place to start!



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    5 Discussions


    5 years ago on Introduction

    Have you thought of the magnet/etc attached to the lid? This way you would be shining it down into the canister, it could also be turned over for a smooth top. It would make getting the battery out to change it as well :)

    Good work though. I might just have to do this myself!

    2 replies

    5 years ago on Introduction

    Great Instructable - Keep up the good work.

    How about getting to grips with one of the free schematic capture packages for drawing circuits. This would improve the clarity of your circuit diagrams; essential once you start to draw more complex ones.  Many also feed into a PCB layout package which you'd need if you want to get into making your own boards. There's many around but beware as some tie you into their board manufacturer. I use the free version of DIPTrace.

    The reason your LED sometimes flashes is that it's reacting to the additional light from the LED as above the 'turn OFF' threshold, then reacting to the dark again so turning ON . . .    Maybe angling the sensor towards the front of the container would sort this.

    BTW - LRD should read LDR - Light Dependent Resistor.

    1 reply

    Thanks for the tips and suggestions!

    Apologies about the LDR. That had to be annoying to read. Thanks for reading even with the glaring mistake :-)