LED comparisons

[Alren Yewick]

A lot of places use Cree high power LEDs, and US have their own LEDs. I want to do a custom build using a US body, but I want a pretty unique blade color that will involve some color mixing. I looked at US first, but tgere isn't really an option for that. And I can't find any Cree boards with color. I was looking at Storm Mini LED Light Circle (Multi-color / 12V / JST) but I'm not great with understanding power usage of lighting or brightness. Would these work okay, or are they too dim?

[Alren Yewick]

I'm extremely open to suggestions BTW.

[Infinit01]

Hey there, Alren.

A few things that you need to have when calculating what you need for LEDs.

Using Ohms Law which states that the current through a conductor between two points is directly proportional to the voltage across the two points. ... More specifically, Ohm's law states that the R in this relation is constant, independent of the current.

That formula is V = I × R, where V is the voltage, I is the current, and R is the resistance. But how do you know what numbers to plug into that formula to get out the right resistor value?

1. Forward Voltage
This is found on the LED unit

2. Forward Current
Also found on the LED unit

3. Supply Current
Found on your battery setup (6 volts for 4 AAA, 7.4 volts for two 14500, etc.)


Lets start with a concrete example. Suppose that we are using a 2 × AA battery holder (like this one from our shop), which will provide us with a 3 V of power (with two 1.5 V AA cells in series; we add the voltages), and we’ll plan to hook up a yellow LED (like one of these).

LEDs have a characteristic called “forward voltage” which is often shown on the datasheets as Vf. This forward voltage is the amount of voltage “lost” in the LED when operated at a certain reference current, usually defined to be about 20 milliamps (mA), i.e., 0.020 amps (A).   Vf depends primarily on the color of the LED, but actually varies a bit from LED to LED, sometimes even within the same bag of LEDs. Standard red, orange, yellow and yellow-green LEDs have a Vf of about 1.8 V, while pure-green, blue, white, and UV LEDs have a Vf of about 3.3 V. So, the voltage drop from our yellow LED will be about 1.8 V.

The V in our formula is found by subtracting the LED’s forward voltage from the voltage of the power supply.

3 V (power source) – 1.8 V (LED voltage drop) = 1.2 V

In this case, we’re left with 1.2 V which we’ll plug into our V = I × R formula.

The next thing we need to know is the I, which is current we want to drive the LED at. LEDs have a maximum continuous current rating (often listed as If, or Imax on datasheets). This is often around 25 or 30 mA. What this really means is that a typical current value to aim for with a standard LED is 20 mA to 25 mA—slightly under the maximum current.

Aside: You can always give an LED less current. Running an LED near its rated maximum current gives you maximum brightness, at the cost of power dissipation (heat) and battery life (if you’re running off of batteries, of course.) If you want your batteries to last ten times longer, you can usually just pick a current that is only one tenth of the rated maximum current.

So, 25 mA is the “desired” current— what we’re hoping to get when we pick a resistor, and also the I that we’ll plug into our V = I × R formula.

1.2 V = 25 mA × R

or rephrased:

1.2 V / 25 mA = R

and when we solve that we get:

1.2 V / 25 mA = 1.2 V / 0.025 A  =  48 Ω

Where “48 Ω” is 48 ohms.  (The units are such that 1 V/ 1 A = 1 Ω; one volt divided by one amp equals one ohm.  If you are dealing with current in mA, convert to A by dividing by 1000.)

Our version of the formula now looks like this:

(Power supply voltage – LED voltage) / current (in amps) = desired resistor value (in ohms)

We end up with a resistor value of 48 Ω.  And, that’s a fine starting resistor value for use with a yellow LED and a 3 V source.

Let’s look at resistor values for a moment.  Resistors are usually available in values such as 10 Ω, 12 Ω, 15 Ω, 18 Ω, 22 Ω, 27 Ω, 33 Ω, 39 Ω, 47 Ω, 51 Ω, 56 Ω, 68 Ω, 75 Ω, and 82 Ω (and their multiples, 510 Ω, 5.1K Ω, 51K Ω, etc.), and (unless you specify higher precision while shopping) have a tolerance value of about ±5%.

If you do a lot of electronics projects, you’re likely to have a bunch of resistors lying around. If you’re just getting started, you might want to get an assortment so that you have some handy. Resistors also come rated to handle varying amounts of power— resistors rated for more power (more watts) are able to safely dissipate more heat generated within the resistor. 1/4 watt resistors are probably the most common, and are generally just fine for simple LED circuits like the ones we’re covering here. (We’ve discussed power dissipation previously—look into that when you start to move beyond these basics.)

Now, the resistor value we calculated above was 48 Ω, which isn’t one of our common values. But that’s okay, because we’ll be using a resistor with a ±5% tolerance, so it won’t necessarily be exactly that value anyway. To be on the safe side, we generally select the next higher value that we have on hand; 51 Ω in this example.

If you used the example setup, you would use the following:
3 V battery box, 51 Ω resistor, and yellow LED.

[Cyclops942]

Point to Infinit01 for the explanation!

[chalion]

Problem with color mixing, is that you really need a RGB LED module and a controller for it. UltraSabers does this by using either their Emerald driver board for LED control only, or the Diamond controller, to allow customization of the LED and sound. With either, you can adjust to the minutest color variation you can find, at a higher cost than a simple 1 color, or even a tri-cree LED costs.

You can find RGB LED's in the size that will fit into a US hilt (LED is @ 21 mm diameter) that fits in a LED module that US also sells separately. NOTE: The RGB LED US uses has 8 leads, so if you want to play with an 8 lead LED to get the color you specifically want, without using a controller, you would need to play around with different resistors to figure out what color you can get. It may cost a bit more, but an Emerald or Diamond would allow you to get the exact color you want, then be able to change it to another color, without tearing the LED out every time you want to change colors.

The Storm Mini LED Light Circle you listed in your post, seems like a viable alternative, except for 3 things: There's only 7 preset colors and it's 30 mm diameter (1 inch and 3/16) without heatsink and module to set into an US hilt. US module outer diameter is only 1 inch (same as the blade diameter), which would preclude using the storm. Many of the US hilts have removable emitters, so you could possibly use the storm, but it would be annoying to get it to fit. I'm not sure what lumens the Storm emits, but the Luxon and Cree LEDs are more focused and will light up the whole blade. I suspect the storm won't. My Reaper had a 34 mm socket area where the emitter screws onto, but its' not very deep, only @ 15 mm, including the threading to hold the emitter.

Third thing is the power requirement: Use it with 3S battery (10~13V) only. US uses 2-3.7v batteries for 7.4 volts total.

[Cyclops942]

Point to chalion for this explanation, too, especially since it contains some cautions that could save people LOTS of frustration and cost.

[chalion]

Another note: If someone didn't want to be able to change to any color, but instead wanted, for example, royal blue, but pale, you could buy a tri-cree led (royal blue, royal blue and white) and change the resistance on the white to allow it to be brighter. But the overall color will be royal blue.

3 color LEDs (all 3 diodes the same color) would all push out much more light, but would always be "on" that specific color.

[Infinit01]

Point to Infinit01 for the explanation!

Thanks, Cyclops! I really geek out over this.

[Alren Yewick]

Thank you guys so much! Infinit01 and and Chalion! Both responses were so helpful! I'm really excited about this and glad to have run in to some more experienced individuals! This helped me figure out how I'm going to set up the electronics, I believe.
 My question for color mixing would be, If I wanted to do a tricree, if I mixed a blue and two yellow, and had the blue at a less bright output, would it give me something close to what I'm looking for? Worst case, I'll just do a lime green. But I'm hopeful for a green yellow.

[Alren Yewick]

Also here are the "stats" for the LEDs in the tri cree
 
Amber Cree Part
107 Minimum Luminous Flux @ 350mA
Forward Voltage @1000mA = 3.28v

Blue Cree Part
45.7 Minimum Luminous Flux @ 350mA
Forward Voltage @1000mA = 3.4v

So I guess my question would be, since there would be two yellow, and one blue, I'd need a power source of more than 9v? In addition my activation switch has an LED ring, and it will need a resister of its own.
If I'm understanding correctly, In order to have enough power for everything, let's say I'd use a battery pack with 4 lithium ion AA at 3v each.
I'm having trouble on the math since the numbers on these LEDs seem a lot higher than the example. I used a conversion app that deals with this and it says a resistor of 8.72Ω but that doesn't seem correct to me. 

[firehand10k]

You are pretty close to correct if you wire them all in series If you wire them in parallel instead you will need more current instead of more voltage. You can safely run all of those with a single 18650 LiIon cell at 3.7 volts allowing more space inside and reduced weight or even 2 of the 14500 cells US uses but the needed resistors will be different.
Also amber LEDs are not yellow. They have a distinctly orangish tint to the yellow that will affect how your colors mix. If you wire in parallel you can try out different resistors at or higher than needed to fine tune your color mixing.

[chalion]

You are pretty close to correct if you wire them all in series If you wire them in parallel instead you will need more current instead of more voltage. You can safely run all of those with a single 18650 LiIon cell at 3.7 volts allowing more space inside and reduced weight or even 2 of the 14500 cells US uses but the needed resistors will be different.
Also amber LEDs are not yellow. They have a distinctly orangish tint to the yellow that will affect how your colors mix. If you wire in parallel you can try out different resistors at or higher than needed to fine tune your color mixing.

Point.

Suggestion: Before actually destroying (I mean, modifying) your lightsaber, I would suggest buying a breadboard or 2, get the supplies you're thinking of needing and then plugging it all into the breadboard to see if it all will work. This at least will save yourself the soldering, wiring mistakes/wrong resistors, then re-soldering to see if you got it all correct.

[Alren Yewick]

Firehand10k
With the tri cree, i believe it is run in parallel, so I will need more current, so a smaller resistor?

[firehand10k]

A tri-Cree can be wired either way. It all depends on how much space you have how much you want to use and what other components you want to use. I have used them with a single cell and 3.7 volts with a small resistor on each and with larger resistors on a 2 cell setup running at 7.4 volts. And in a combination of series and parallel with two cells and a buck puck as US does them.

 You need to plan the whole project and decide how you will mount your batteries and how many will be used. If you are using sound what board and what power supply does it need  and how does it relay to the LEDs? Is it direct drive or does it offer any controls.?

As challon said it is a very good idea to get a breadboard and try out different combinations to see what you like best.

We're giving basic answers that can be applied broadly but with more specific information on what you want to work with as a while better guidance could be offered.

[Alren Yewick]

Ah, that makes sense. Here is what i have so far.

Amber Cree
107 Minimum Luminous Flux @ 350mA
Forward Voltage @1000mA = 3.28v
^ 3 of these in the tri cree set up.

16mm Anti Vandal Latching switch, blue ring LED.
"There is no internal resistor on these so you need to use the correct resistor in order to not fry the LED. The LED has a forward voltage of 3.3V and runs at 20mA. 4.8V would use a 82ohm 1/4 watt resistor, 6V would use a 150ohm 1/4 watt resistor. Please ask if you do not know."

Power Supply.
7.4v Li-ion 800mAh 14500 Battery Pack
Made with 2x 14500 cells (AA sized) and it is PCB protected.
Size is 1.96" x 1.12" x .61"
These are wired with a JST connector that is compatible with the Modular Wiring System.
"DO NOT use L-ion batteries if you do not know the dangers of using them, and do not know how to handle them."

I also have a focusing lens for the tri cree, and a heat sync.

This is the parts list so far. Is there anything else necessary for a basic stunt saber?  I may some day want to add sound, but I will rewire the set up, if I decide to do that. So for now, let's focus on just a stunt saber.