White Leds

Question: How long can three white LEDS run off AA batteries? Hi. I'm doing a POS design and need to incorporate 3 white LEDs. The thing is, they'd like it to run off of batteries. What would be a good solution battery-wise if I needed the LEDS to run for maybe 3 months? Anyone?

Answer: Select the LEDs, look up the forward current, multiply by three months and size the batteries to suit. example (other components required) a 3mm 1.5mc white led has typical forward current of 20ma at say 3V (pair of batteries) means each battery gives 30mW Duracell graph shows this will last 100 hours. You need many many batteries to last 3 months! You could: 1) reduce the current and the light output to extend the life 2) have a timer to turn off at night/ unoccupied 3) flash the lights, may be more attention getting and power saving.

Question: What size resistor do i need for 4 red leds, and 4 white leds? Supply voltage is 3v, Red leds have forward voltage 1.8v and use 20ma, white leds have forward voltage of 3.3v and use 25ma...i do not know what resistor i would need because the leds are different

Answer: Red: 3v - 1.8v = 1.2v, 1.2v/0.02A = 60ohms, nearest prefered value is 56ohms. White: Can't do it, as the supply voltage is less than the Vfwd. It will probably glow a little though.

Question: in texas is illegal to turn your turn signals blue or to turn your reverse lights to white leds? so my turn signals can only be amber? what about my amber reflectors, am i required to have those or can i take those out?

Answer: Blue for indicators. NO. It is red or a yellow for a reason. In dark or on a snowy or a heavy rainy day one can be seen clearly. They have come up with these rules after extensive research and tests. Automotive safety is a major issue and the research engineers keep improving things after a lifetime of study and experiments. So, you cannot screw around with safety issues. White for reverse, OK. and no other color.

Question: How to connect 8mm Ultra bright white leds to Car Battery, please provide circuit?

Answer: not sure where your putting them, but LEDS are polarity sensitive which means one of the little wires coming out the bottom has to go to the positive and the other one to ground, and they WON'T work in reverse! let me know the details of the installation and i'll tell u how to hook them up, but sorta depends on what your doing with them!

Question: How to connect 8mm Ultra bright white LEDs of 10 Nos to Car Battery of 12V, please provide circuit?

Answer: Your question makes no sense. You need to know the specs of the LED to calculate the correct value of resistor to prevent burning out the LED . I'd sign up over here : http://www.oznium.com/forum/

Question: What is the value of the Resistor to be used for 10 Ultra white LEDs connected to Car Battery of 12v?

Answer: It all depends, how you connect them. How many in parallel, how many in series? What is their voltage drop? How many mA do they need to glow? The LED calculator has some examples that should help you http://metku.net/index.html?sect=view&n=1&path=mods/ledcalc/index_eng

Question: What is the attenuation experienced by white LEDs?

Answer: . Would you like to ask the question in a different way? Do you mean how efficient are white LEDs?

Question: How long would two CR2450 batteries power 4 white LEDs?

Answer: If you are connecting the CR2450 batteries in series, you would get 6-volts with a nominal capacity of 610mah. A typical LED will draw about 30 milliamps, so 4 LEDs wired in parralel would draw a combined total of about 120 milliamps. At this rate, the LEDs would operate for approximately 5 hours.

Question: i have 3 bright white leds and a 9.6 volt batters? i have 3 bright white leds and a 9.6 volt batters and what should i add so the leds dont burn

Answer: This question requires more information to give you an exact answer. Basically, you will need a resistor. But the size & type depends on factors such as: 1. Voltage Drop across each LED 2. Desired LED current 3. If the LEDs are hooked up in series or parallel For example, if your LEDs are rated at 3.5v@20mA Hooking them up in parallel would require a 120 ohm, 1/2 watt resistor. The same 3 LEDs in series would need a 150 ohm 1/8 watt resistor.

Question: Hooking up LEDs... Warm White/Pure White? Resistors? I am using some LEDs on a small project of mine. However, I know very little about LEDs in general. You see, I only need about 6 or 7 of them to light up what I need. I bought some very thin wire from Home Depot, soldered them to the LED, and hooked them in place to an existing socket from a LED Christmas string of lights. They worked fairly well!! But some of the Pure White and Warm White LEDs became really dim after a few days...then brightened back up over a few days. What caused this??? Note that I have not used any resisitors in this project since I figured the already-existing string would have built-in resistors already. If I were to ditch the Christmas LED string and buy a plug from Radio Shack and hook them up individually, what voltage plug would I need? I already have a 3V. Also what Ohm Resistors should I use? The 1/2 watt 330-Ohm and 1/4th watt 100-Ohm make the LED much too dim. Anything much bigger would triple the size of the wire!! Suggestions? Please help!

Answer: Check out the site I linked below. It's full of articles and descriptions of experiments done by the author. He helped me understand a lot about LEDs. He also wrote a "review" of what he thinks of the LED Christmas lights and why he doesn't like them. Most of the LEDS I've seen advertised require 1.5V and 20 to 30 mA. The wattage of your resistors shouldn't change the brightness (I don't think) - it's the ohm resistance that does it. On the LED Center site (below) he has a "calculator" where you can enter your system voltage and the number of LEDs and it will show you what resistor to use.

Question: How easily can I replace the white LEDs in my LED party glasses with blue LEDs? I don't have a photo of the glasses unfortunately, and I'm an amateur. There are 4 small white LEDs I want to replace. How easily can I replace the white LEDs with blue LEDs? Great answer! I'm an amateur, but I've done similar work a few times before. I just hope I get the right blue LED, and luckily I have more than 1 pair of these glasses so in case I screw up I can change the LEDs on the other one(they're cheap too!).

Answer: White and blue LEDs usually have similar characteristics - or at least similar enough that you should be able to unsolder one and solder in the other. Just try to do the soldering quickly, so that the LEDs and the surrounding circuit does not get damaged from sustained heat. Also, you DO have to get the polarities right. IF you have a volt meter, you can test across the LEDs that are IN the circuit to see which side is positive. When you get your new LEDs the slightly longer lead of the two will be the positive side. Give it a try. You might not get it right the first time, but you will learn a lot more than if you did not try!

Question: How do I go about putting all leds in my 1999 honda prelude? I want to put white leds in the gauges, cruise conrol, sunroof button, gear shifter light, clock light, temperature control, pretty much everything that is orange. Anyone have any advice? I want to make sure I get all the right bulbs. Please help. Thanks.

Answer: I've seen kits on ebay for that.

Question: Ok...so i have 10 white LEDs that i need to light up....? Im in between using 3V or 9V or something in between how would i light up 10 LEDs in a circular pattern? i need help finding out how much power needed and the number/magnitude of resistors? thanks in advance

Answer: So you are making an Iron Man micro-fusion device (cosplay?). Okay. You should look at the datasheet for the LED just to familiarize yourself with design considerations, they will also have a test circuit that you can use to calculate what you need as far as a battery and resistor. Here's one that may be like yours: http://www.surplustronics.co.nz%2Flibrary%2FMega-White-LED.pdf You want "If" to be less than 20mA (~18mA) and count on "Vf" being around 3V. Put in the value of the battery you wish to use (say 9V) Rx = (V - Vf) / If = (9-3) / 0.018 = 333 ohms, one for each LED. To the plus side of the batt. you'll have the pos. bus. To the negative side of the batt. you'll have the gnd. bus. You'll have 10 Resistor/LED circuits soldered into place parallel to each other so that it goes "POS BUS to Resistor to +LED- to GND BUS". Good luck and have fun!

Question: Is it legal to have white lights behind my front grill? I was thinking about putting some white leds behind my front grill so it would shine on the radiator and reflect back through the front grill. I was wondering if this was legal. I know other colors of lights are illegal but is white illegal for this purpose?

Answer: that should be legal.

Question: Are White LEDs Converted to Ultraviolet LEDs by exposing them to radiation? Just Wondering What Effects Gamma Rays have on LED's

Answer: "Most "white" LEDs in production today are based on an InGaN-GaN structure, and emit blue light of wavelengths between 450 nm – 470 nm blue GaN. These GaN-based, InGaN-active-layer LEDs are covered by a yellowish phosphor coating usually made of cerium-doped yttrium aluminum garnet (Ce3+:YAG) crystals which have been powdered and bound in a type of viscous adhesive. The LED chip emits blue light, part of which is efficiently converted to a broad spectrum centered at about 580 nm (yellow) by the Ce3+:YAG. The single crystal form of Ce3+:YAG is actually considered a scintillator rather than a phosphor. Since yellow light stimulates the red and green receptors of the eye, the resulting mix of blue and yellow light gives the appearance of white, the resulting shade often called "lunar white". This approach was developed by Nichia and was used by them from 1996 for manufacturing of white LEDs." White LEDs can also be made by coating near ultraviolet (NUV) emitting LEDs with a mixture of high efficiency europium based red and blue emitting phosphors plus green emitting copper and aluminum doped zinc sulfide (ZnS:Cu,Al). This is a method analogous to the way fluorescent lamps work. However the ultraviolet light causes photodegradation to the epoxy resin and many other materials used in LED packaging, causing manufacturing challenges and shorter lifetimes. This method is less efficient than the blue LED with YAG:Ce phosphor, as the Stokes shift is larger and more energy is therefore converted to heat, but yields light with better spectral characteristics, which render color better. Due to the higher radiative output of the ultraviolet LEDs than of the blue ones, both approaches offer comparable brightness. The newest method used to produce white light LEDs uses no phosphors at all and is based on homoepitaxially grown zinc selenide (ZnSe) on a ZnSe substrate which simultaneously emits blue light from its active region and yellow light from the substrate. A new technique just developed by Michael Bowers, a graduate student at Vanderbilt University in Nashville, involves coating a blue LED with quantum dots that glow white in response to the blue light from the LED. This technique produces a warm, yellowish-white light similar to that produced by incandescent bulbs." From Wikipedia, the free, online encyclopedia at: http://en.wikipedia.org/wiki/Led Hope this helps!

Question: You can purchase what are called “White LED’s”. Why aren’t these truly considered white light emitting LEDs?

Answer: That depends only on your definition of white. For most practical purposes they are white, but their spectral content does differ from sunlight.