# Light circuit for an art project

Discussion in 'LEDs and Optoelectronics' started by leigh, Apr 13, 2012.

1. ### leigh

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Apr 13, 2012
Hi everyone,

I want to create a circuit that will have around 150 blue grain of wheat bulbs (12 volt), powered by a battery that will light up when a push switch is used.

HOWEVER, I don't know the first thing about power and circuits! Do any of you have any advice on the best way of creating this circuit and the amount of power it will require? I am also concerned that if one bulb breaks, the circuit will be broken and no longer work.

Any advice would be greatly appreciated!

Thank You
Leigh

2. ### Harald KappModeratorModerator

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Nov 17, 2011
That depends on the bulbs you use. If they are like these http://www.microminiatures.co.uk/acatalog/gow2.html, they need 80 mA @12 V each. Total current is then 150 * 80 mA = 12 A.
12A * 12 V = 144W.
If you connect the bulbs in parallel, only a defect (broken) bulb will be off. all others will stil be on.
If you connect the bulbs in series, a single defect bulb will turn off the full chain of bulbs. But if you want to connect them in series, you need 150* 12 V = 1800 V - rather impractical for a battery and dangerous besides. So a series circuit is not an option at all.

What voltage does the battery have you intend to use?

Harald

3. ### Harald KappModeratorModerator

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Nov 17, 2011
Last edited: Apr 14, 2012
4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
If the bulbs are rated at 12V then you connect a wire from your battery to the switch, from the other side of the switch to one side of all of the lamps. The you join the other end of all the lamps together and connect that to the other side of the battery.

This is called connecting the globes in parallel.

The power required will be 150 times as much as is required for a single bulb.

5. ### leigh

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Apr 13, 2012
Hi guys,

Yes, those are the bulbs I plan on using. Can you suggest a safer power source for so many bulbs? And what would be the required power if it was a parallel circuit?

I've made a veery small scale mock up of the circuit using 2 bulbs and a 9v battery, but obviously the larger scale version will be using a LOT more bulbs!

Also, I'd like to apologise for double posting this topic. I've not used a forum before and realised I'd posted the original under the wrong themed forum.

6. ### BobK

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Jan 5, 2010
You might want to think about using blue LEDs instead, they will use much less power.

Bob

7. ### leigh

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Apr 13, 2012
Thanks Bob, I'll look into it!

8. ### leigh

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Apr 13, 2012

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Aug 13, 2011
For an art project, viewing angle may be an important consideration. While a grain of wheat light bulb will have a similar point-of-light appearance from all angles except through the base and leads, an LED is an inherently directional source. How directional varies from one to another but angles of 45 or 60 degrees are common and 120 degrees is near the upper limit.

LEDs have the advantages over light bulbs of lower energy use, less heat generation, intense and consistent color without a filter and tight directionality if needed.

It would help to know whether your project involves direct viewing of the light sources or they are being used to illuminate something. If they are being directly viewed, do they need to appear as points or should they be diffuse and what viewing angles need to be accomodated? Will there be a requirement for the brightness to change or remain the same at all times?

10. ### CocaCola

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Apr 7, 2012
I don't know how much room you have for the lights, but 5mm STRAW HAT (strawhat) style LEDs produce a very convincing filament lamp look... They still suffer from being more front directional but not horribly... Again I emphasize straw hat style, they are basically squatty wide profile LEDs, and thus have a completely output appearance...

11. ### leigh

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Apr 13, 2012
You raise some good points! The work I want to create will be a wall mounted torso of the human body, laser cut from perspex. The lights with trace the lines of the veins. The audience will be looking at the bulbs straight on but with a 'birds eye view' of the bulbs, with the top of the bulb facing them. I will use a push switch so that the bulbs are not left on constantly, just when the viewer pushes the button to complete the circuit. I want all the bulbs to have the same brightness throughout.

I hope this makes sense!

12. ### leigh

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Apr 13, 2012
I'll be honest, I didn't have a clue what a straw hat LED was, so I googled it and learned something new! However, from the images I looked at it appears as though they give off quite a wide angle of light, and I wonder if 150-200ish of these would look a bit too bright or blinding?

13. ### CocaCola

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Apr 7, 2012
Time to learn about current limiting and LEDs

Or get real fancy and learn about PWM and using it to dim LEDs

14. ### leigh

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Apr 13, 2012
what one is easiest?

15. ### CocaCola

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Apr 7, 2012
Current limiting is easiest, the larger the value of the resistor used the dimmer it gets until it reach the threshold where it just goes off... You will have to experiment hands on with different value resistors until you find that sweet spot... I suggest you get a bundle of 10 Ohm resistors for testing, you can pair the 10 Ohm resistors up in series or parallel configurations and get just about any value resistance you might need... Or if you have a multimeter, you can simply substitute a trimmer pot for the resistor, dial it to the proper brightness and measure the resistance, and then secure the proper resistors...

This calculator will diagram your circuit, once you plug in the right values...

http://led.linear1.org/led.wiz

Changing the value of the resistors will vary the brightness of the LEDs... Doing them in this series/parallel arrangement is energy efficient, and cuts back on the number of resistors needed...

1,114
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Aug 13, 2011
Current limiting; PWM would only have been necessary if you wanted to change the brightness gradually during viewing.

Your description of your project makes it clear that diffuse LEDs would be a better option than clear ones, perhaps in more than one size if you're representing large and small veins.

On a side note, this project might also have been done using FTIR (frustrated total internal reflection) techniques or EL (electroluminescent) wire.

17. ### CocaCola

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Apr 7, 2012
Another option you might want to consider, since you are just outlining a path is electroluminescent wire or EL wire, you can get entire little kits with the transformer all over Ebay (or other sites) for cheap... Think of it as thin plastic neon like tubing that is easy to twist and bend...

*** post crossed paths with KJ6EAD

18. ### leigh

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Apr 13, 2012
Thanks for all the info guys! I'll do some research tomorrow and get back to you all. Thanks again for all your help!

19. ### CocaCola

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Apr 7, 2012
And another option I will toss up since you are using a laser cutter, you might want to consider leaning towards KJ6EAD idea, carving the paths into the perspex and using simple side lighting of the perspex... When lit from the side the cut in paths in the perspex will glow exponentially more then the rest of the sheet, producing a neon like effect... If you put a solid cutout of perspex in the front (maybe slightly tinted) and mount an engraved blue one behind it, when you side light the one in the back, poof all the paths will glow blue....

This type of lighting is the new trend in 'cheap' alternative neon looking signs...

A quick and dirty overview of this technique...

http://www.instructables.com/id/Awesome-LED-Edge-lit-Desktop-Nameplate/

Last edited: Apr 13, 2012
20. ### Harald KappModeratorModerator

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Nov 17, 2011
The power requireemnts are in my first post.

If you are going to use LEDs and a 12 V battery, do not add the LEDs in parallel as you'd do with light bulbs.

1) you need a current limiting series resistor.
2) if you are going to power one LED (V=1.6 V ... 3 V depending on the type) from a 12 V source, you need to drop 10.4 V...9 V across the series resistor. This is a waste of energy. Instead put some LEDs in series, then connect these packages in parallel.

Example:
Assume you use blue LEDs with ~ 3V operating voltage.
Add 3 LEDs in seriues -> 3*3 V = 9 V.
The series resistor now "sees" 12 V - 9 V = 3 V.
For a current of e.g. 20 mA, the resistor is 3 V / 20 mA = 150 Ohm (147 Ohm is the next standard value).
For 150 LEDs in total you need to built 50 of these packages.
Each package uses 12 V* 20 mA = 0.24W of power. In total 50*0.24W= 12W.

A nice savings compared to light bulbs.

Harald