Info on using and determining dropping resistors is in my LEDs 101 File. That file also explains why it is usually not good to connect an LED directly to a fixed voltage source.
Now for the other frequently asked questions:
Where do I get blue or white LEDs with a voltage drop less
than 3 volts?
How do LED flashlights work with just one battery?
How do LED keychain flashlights get away with no dropping
resistor?
Where do I get infrared LEDs with oddball wavelengths such
as in the 700's of nm?
Where/how do I get LED lights for motor vehicles?
Where do I buy XXXX?
I was sent here to look for goodies not mentioned above!
More likely your solution will be using a boost converter.
An LED flashlight bulb with a boost converter built in to utilize 3 volts
is described in Craig
Johnson's Starlite Flashlight and Night Pearl Flashlight Bulb Page.
UPDATE 9/23/2001 - Craig Johnson added a Night Pearl Bulb Page.
There are 1.5V and 3V versions.
One line of blue LEDs with low voltage drops at "usual" currents around 20 mA is the Luxeon series by Lumileds. These have large dice and are designed to run at really high currents up to 350 mA. At 20 mA, a blue sample that I managed to get into my hands had a voltage drop slightly over 2.8 volts and efficiency was good. But I do not expect these to be as useful as boost converters for 2-cell flashlights. Do not expect these to be cheap!
Info:
Lumileds home page,
http://www.lumileds.com
Lumileds' separate home page for their
Luxeon series, http://www.luxeon.com
Full production will start any month now, sometime in the summer of 2001. Purchasing them will normally be from their distributors.
LED flashlight "bulbs" with boost converters built in are available - check out Craig Johnson's Night Pearl Bulb Page.
One old traditional way of powering LEDs from a single 1.5 volt cell was
to use National Semiconductor's LM3909 LED flasher IC. One can pulse the
LED fast enough to appear continuously on, or one can add a diode and a
filter capacitor. However, the LM3909 is generally not the best way and
will not boost 1.5 volts to a voltage that will power blue, white, or
non-yellowish green LEDs. Adding a diode and a filter capacitor is
recommended if you use this to boost 3 volts for blue, white or
non-yellowish green LEDs, since those LEDs are generally more efficient
with steady current than with pulsed current.
Another IC that looks better for this is the Texas Instruments TPS61010DGS.
Craig Johnsom reviews some of these at http://ledmuseum.home.att.net/ledir.htm
Another supplier of oddball wavelength IR LEDs is Plasma Ireland, http://www.plasma-ireland.com. They have a whole line of IR LEDs including 735, 750, 810, 850, 870, 890, 910, 940, 1300 and 1450 nm.
Other suppliers wil be added here when I find out about them.
I have seen some units where the current reached levels that I would call adventurous - especially in Photon models with blue, green or white LEDs. However, you need really heavy use with constantly fresh batteries to damage the LEDs - and any significant LED damage if such currents are sustained will probably take hundreds or thousands of operating hours. I consider it a safe bet that few users of these lights will log 500 hours of use with highly fresh batteries in a lifetime. Normally, the battery can only provide current in excess of the LED's maximum rating for a few minutes. Also, it is not easy to notice if the LED deteriorates to even half its original performance. But if you do notice any fading, chances are something like 99 percent that it will be due to the condition of the battery rather than the condition of the LED.
Lights for cars, especially other than center high-mount brake lights,
are more customized and specialized. Availability is mainly as a
replacement part for a specific car, all too often at a very high price
through a dealer for that make of car. If the light is not at an edge or a
corner of the vehicle, you may get away with a truck light but I do not
guarantee this and I discourage replacing any light unit on your vehicle
with something else unless it is approved by DOT (in the USA that is, or
whatever authority has jurisdiction in your country) and the manufacturer
intended it to be used in your vehicle.
Replacing an automotive incandescent bulb with an LED "bulb" of the same
base style and of the appropriate color will appear to work, but light
output will fall short of requirements. Expect hype in claims of light
output from LED "bulbs" that fit where incandescent bulbs normally go.
In addition, the light distribution pattern will be different and even in
the highly unlikely event you have adequate total light output the amount
of light output into some directions will almost certainly not be in the
allowable range.
Homebrewing a vehicle light requires knowing the lower limit and upper
limit for amount of light into something like 40 different directions so I
do not recomend this.
My LED Top Page, http://www.misty.com/~don/ledx.html for links to manufacturers and suppliers.
Craig Johnson's Where To Buy Page, http://ledmuseum.home.att.net.
My Bright/Efficient LED Page, http://www.misty.com/~don/led.html has a bit of supplier info.
My Page on Nichia, http://www.misty.com/~don/nichia.html has a bit of supplier info, including surplus suppliers and a bit of info on non-Nichia products similar to some Nichia ones.
Craig Johnson's "Punishment Zone" flashlight review page, http://ledmuseum.home.att.net/zone.htm, mentions more LED flashlights than perhaps even he could remember! Plus a few items other than just flashlights.
First, explore My LED Top Page, http://www.misty.com/ledx.html and all links therefrom even if it takes several hours.
If this completely fails so badly that you think you are better off e-mailing a sort-of webmaster with a 50-hour-per-week unrelated fulltime job, then try e-mailing me, at don@misty.com Spammers beware - my sysadmin haas a hobby of tormenting spammers and I encourage and cooperate with him! But I do readm e-mail enough to avoid sending punishment to the innocent!
I have only a 90 percent response rate and my sysadmin just about has a hobby of attacking e-mail spammers. If you can read this file, then it pays you to avoid fancy-ing up your e-mail with HTML-sorts of fancy-ing means since I associate such techniques with e-mailers that I would submit to my syusadmin as "spammers". Spammers who fail to read and heed my advice will have blockage to some of the addresses on those 56-million e-mail-address CD's, or maybe even ISP account termination! My sysadmin gets lots of pleasure and joy from torturing e-mail spammers and he knows how to cause pain! Do not "spam" anyone in the misty.com domain!
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