Creating a Toy Street Lamp

[ToyLamp]

Sorry, stumbled across your forum while trying to solve a problem, and it appears to me that anyone of you could probably help me figure this out.

I'm builing a 1:12 scale building, and on the sidewalk are two street lamps, measuring about 10 inches tall each. The lamps are taken from a toy, but I want to modify them so that they are actually lit. Currently the light is just plastic painted off-white.

The light portion is basically a 3/4 inch sphere. I plan to saw this portion off. However, I cannot find a bulb this size and shape, and even if I could, there's very little room for the base of the bulb.

My idea for a solution is that I've taken some 3/4" acrylic balls, sanded them to frost the exterior, and then drilled into them to accomodate a small bulb.

What I need now is to find a very small light, as bright as possible to put inside. LED seems perfect. I need a bulb that is as bright as I can find, but that has a wide angle of light, and that can easily be wired through the lamp with little or no base.

My two questions then are:
a) Bulb recommendations, what and where to find?
b) What power source? AC, or a DC converter? I'm no electrician, so I need to be spoon fed the electrical.

Any help would be greatly appreciated. The lamp being used can be seen in this pic:

Thanks.

[RGBrainbow]

Hi,
are the lamps meant to light up Your model street or only themselves?
regards
joachim

[ToyLamp]

I don't have expectations that I can make them bright enough to light the entire model, but the closer I can come to it safely the better. I want them to look the correct brightness for their scale, that they'll light the area around them.

[gwbaltzell]

A white LED in each would likely look good. If you could find any of the ones with a milky diffusion in the epoxy, it would give a more even light and no color artifacts as many have. Second choice would be something like this 5 mm (T1-1/5 [3/16"]) 70° inside your frosted ball. LEDs are also available in 3mm (T1 [1/8"]) if you need smaller. Final power supply needs to be current limited DC. For your purpose a wall wart would be fine with a resistor in series with each LED. Take the total number of LEDs you plan to use and multiply by 40. This is the lowest mA rating of a single wall wart. I'm going to suggest 9 V but the resistors can be recalculated for anything from 4 volt and up. The value for a resistor can be had by taking the voltage of the supply and subtracting the Vf of the LED usually 3.6 and dividing by the current 0.02 A (20 mA). This can be plugged into Google™ like this: (9V - 3.6V) / 0.020 A =
We get the answer back: ((9 V) - (3.6 V)) / (0.020 A) = 270 Ohms
And use the next higher standard value resistor. Since 270 Ohms is a standard value, we will use this. Power dissapated by the resistor (as heat) is the current squared times resistance: 270 ohm * (.02 A ) ^ 2 =
270 Ohm * ((.02 A)^2) = 0.108 Watts
or the voltage across the resistor times the current: (9V - 3.6V) * .02 A =
((9 V) - (3.6 V)) * .02 A = 0.108 Watts
Always double this. So 1/4 Watt resistors. If we preferred 1/8 Watt we should use a lower voltage wall wart.
Pay attention to the polarity of the LED, the longer leg is postive. It doesn't matter which leg the resistor goes in series with.

Good luck. Looking forward to pictures of the final layout.

[ToyLamp]

Great. Perfect. Thanks for the info. I'm anxious to get started now.

Another question. This looks like it has very low power consumption. Could it be powered with a simple 9V battery? If so, how long would that be expected to last on one battery?

I really like the wide angle of the 5mm you linked. Can I get something brighter and still maintain a wide angle, or are they inversely related?

[gwbaltzell]

You got the idea right off, this style LED basically output the same amount of light but variation in the packaging give different beam angles and therefore different "brightness" on the surface it illuminates. This is normally measure at one foot and given in mcd (1/1000 candela). This figure is meaningless without the angle.

There is one brighter that you might be able to use but requires careful heatsinking. You might be able to disguises the heatsink as an old fashion wavy metal reflector. The same site carrys these 1.2 W Luxeons and a "puck supply" to regulate the power. The low dome version will provide a fairly wide angle (I think 120° without double checking the spec. sheet) and these are rated by light output (20 lumens). The 5 mm typically are about 3 lumens tops. This makes the Luxeon about 5 times brighter. Human vision is not linear. Surface brightness might not be much brigher because of the wide angle! Current draw is 350 mA each.

Battery power is possible with a few but comes with some more design considerations. For the smaller LEDs, if you are willing to allow the light to dim as they discharge, I would recommend 4 AAs or Ds or a 6 V lantern battery. I would suggest running slightly beyond the recommend high current (will be brighter on fresh cells) but still be somewhat bright when the cell are low. This recommendation is 68 Ohms per LED. There are other solutions that would provide a constant brightness but at a higher cost.

You might prototype the battery - resistor solution, since the cost is low, just to get a feel for it without actually putting it in the model. Cost 2 LEDs (or however many you want), a resistor per LED, battery holder, switch, cells.

If you're in GB or Europe, Maplin might be easier to get some of the parts, they do carry LEDs. In the US resistors, battery holders and switches can be had at Radio Shack and a number of surplus places. I'd buy LEDs and drivers from CPF sponsors (see banners in the forum list) or places recommended in the forum. Typically in the LED section.

[ToyLamp]

How bright is 3 lumens, say, compared to a little Christmas tree bulb. I'm trying to get a sense of just how bright (or dim) that is.

[gwbaltzell]

That is really hard to say. But if pressed I'd have to say similar. Anyone else?

[JanCPF]

Just bear in mind that with the 5 mm leds you'll get a bluish white light as opposed to the warmer yellowish white that incan bulps put out.

Jan

[gwbaltzell]

There are now warm white LEDs if you're trying to recreate the incandesent era. [img]/ubbthreads/images/graemlins/wink.gif[/img]

[JanCPF]

[ QUOTE ]
gwbaltzell said:
There are now warm white LEDs if you're trying to recreate the incandesent era. [img]/ubbthreads/images/graemlins/wink.gif[/img]

[/ QUOTE ]

But can you get them as 5 mm leds? I thought you could only get the warm whites as Luxeons.

Jan

[gwbaltzell]

Nichia makes some and thery are on their direct order site.
I have seen Super Bright LEDs list them before, but none currently on their list.
May be harder to find than I thought! Checked Craig's site The LED Museum to see who else makes them and didn't find any! Craig?
None at All Electronics.
None at Best Hong Kong.
Nada at Alltronics
Quickar has Nichias but no warm.
Zip at Digi-Key. No whites listed?

Who have I missed?

edit: a 20° one at The LED Light. And they have some of the milky cool whites! Min. order 6 pieces at $1.95 each.

edit again: The original link I gave you may be for a milky 70° (photo may be wrong). I ordered one when I ordered my EverLED and got a milky. If I can find my paperwork I'll let you know.

edit: corrected Nichia direct link info.

[The_LED_Museum]

[ QUOTE ]
gwbaltzell said:
...May be harder to find than I thought! Checked Craig's site The LED Museum to see who else makes them and didn't find any! Craig?...

[/ QUOTE ]
The only warm white LEDs I know about are the Luxeon Star ones. Not 5mm ones. [img]/ubbthreads/images/graemlins/frown.gif[/img] [img]/ubbthreads/images/graemlins/jpshakehead.gif[/img] [img]/ubbthreads/images/graemlins/frown.gif[/img]

[gwbaltzell]

Craig

I'm surprised no one at Nichia sent you samples!
I may have to order 6 though I'm not really interested in this color. I do like the milkys, however, and disappointed they stop making the 3 mm ones. A milky on Craig's site. Scroll down to the Nichia NSPW515BS.

George

[gwbaltzell]

correction: warm whites are on Nichia's direct order site, original post corrected. look for NSPL

[ToyLamp]

Just wanted to get back to yall and let ya know I finally finished my street lamps, and I'm very happy with the result. Couldn't have done it without your help. Thanks.