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There are a few LED night light projects on the site, but I wanted something a little larger. My kids currently use desk lamps with little 15watt globes in them and I wanted something that threw as much light but a a fraction of the power cost.

This project uses Blue LEDs rated at 15,000mcd housed in a glass jar filled with glass beads to diffuse the light. I also wanted to put a Light Dependant Resistor (LDR) in the mix to shut the LED off once the light in the room was bright enough.

The only thing I had to buy was the glass jar and the glass beads which I got from my local homewares shop. The jar was $2 and the beads were about $8. The other electronic parts are really optional and were bits and pieces I had lying around.

The parts are:
1) A piece of wood (approx 150x250mm 18mm thick)
2) Glass jar
3) Glass beads
4) A left over mobile phone charger (the one I had out puts 9v DC)
5) An LDR
6) NPN transistor
7) 10kohm resistor
8) 100ohm resistor
9) 10k ohm trimpot
10) 4 LEDs

You'ss see me build two here, one for each of the kids, but my parts list above is for one.

(There are no notes on the photos because it does not seem to be working)

Step 1: Cut the Wood

I used an old off cut of pine board as my base and sized it in proportion to the size of the jar, just for fun I cut the corners off and used a router to round the top edge off.

Using the jar lid as a template I drew a circle on the board and again using my router, I cut a recess out of the surface of the board in which the jar lid could sit.

The lid now sits towards the 'back' of the base, I drilled a 4mm hole directly from the rear of the board towards the recess - this is where the power cord will come in.

I then drilled a similar hole from the front through to the recessed area where the LRD will sit and its wire run. Finally a larger hole was drilled in the surface of the board (intersecting with the LDR hole) where the power switch will sit.

Drill holes in the jar lid to match the hole in the base board.

Step 2: Electronics

I had some LEDs left over from the 4x4x4 LED Cube project I did, these LEDs are rated as follows:
Brightness:  15000 mcd
Forward Voltage: 3.2V
Forward Current: 20mA
Wavelength: Typ. 465nm
Size: 5mm
Lens Color: Water Clear


I planned to have four LEDs stacked one on top of the other making them in parallel, then using one of the many LED resistor calculators you can find online, I determined the resistor I should used.

In this case I had a mobile phone charger that supplies 9v, and LEDs with a voltage drop of 3.2 and consume 0.02A.
So using R = (Supply_Voltage - Forward_Voltage) / (Total Current)
R = (9 - 3.2) / (4 x 0.02)
R = 72.5 ohms

The nearest standard resistor is 82 ohms and the nearest one I had in my draw of bits and pieces was 100 ohm - so that will do, the LEDs just won't be quite a bright as they could be.

The circuit diagram attached shows the circuit I used to control the LEDs, I just stacked three more LEDs on top of the one shown. I also included a switch on the positive rail to turn it all off. 

Make sure you wire in the power, LDR and switch after you have threaded then through the wooden base piece, other wise you'll be doing it twice.

Step 3: Finishing Up

Simply fill the glass jar with the glass beads progressively as you place the tower of LEDS up the middle, fernaglling it around getting it to sit how you want it.

I used PVA glue to stick the lid to the wooden base and use a two pack epoxy glue to stick the switch in its hole and the LDR in its place.

Up turn it and you're in business - quite a bright night light for a fraction of the watts!

<p>Completely blue light is probably a poor choice for a night light given the effects of blue light. (see http://www.health.harvard.edu/staying-healthy/blue-light-has-a-dark-side) Incandescent lights don't cause that kind of issue, I don't think. Green leds or maybe some RGB ones (i.e. you can control how much of each color is present) if you can find them with enough mcd would probably be a better choice.</p>
what is the value of the power supply? Do I need a transformer or just a battery? tnx<br>
I just used a spare mobile phone charger that was laying around. Based on the LED specs I calculated what resistor to use (formula is in here somewhere).
tnx<br>
I created your curcuit and it didn't work, I used a BC337 transistor, any suggestions?
This is really cool!

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