I have a white LED keychain light, and it uses a 3volt watch battery with no dropping resistor. So running white LEDs from 3volt logic ought to be a piece of cake. Running them at less than 4 volts must reduce brightness some, but they are still quite bright at 3 volts. ----- Original Message ----- From: "Russell McMahon" To: Sent: Thursday, August 24, 2000 7:38 PM Subject: [EE]: White LEDs > The following comment from a friend may be of interest. > A torch using eg a single Alkaline AA cell and an inverter with an 80% mean > efficiency (hard but not impossible) would give around a 25 hour continuous > battery life. Efficiency is said to be several times that of fluorescent > which in turn is several times that of incandescent bulbs. > > RM > __________________________________________________________ > > Have purchased several 5,600 mcd white LED's from DSE (cat Z3981, $9.95 ea > retail). > > They come with a brief data sheet which includes a prominent warning > regarding possible eye damage. This warning is not "nannying" - these > devices are truly stunning in terms of brightness at 20mA If. They are even > uncomfortably bright at 2mA, and usably visible (as a status indicator) at > 50 uA. > > I predict (as I'm sure others already have) that the days of incandescent > bulbs (and probably gas-discharge type lamps) are now numbered. Someday all > light sources will be phosphor-coated LED's. Buying shares in Nichia may be > a smart move. > > They do however have one limitation at present (other than cost). Their > emission is broad-spectrum but far from flat - a narrow peak at 460nm (100% > relative intensity) > with a wider peak at 560nm (50% relative intensity) separated by a minima at > 500nm (25% relative intensity). Emission is minimal below 425nm and above > 750nm. They can be filtered for other colours but the results will vary > depending on the actual colour sought (don't believe people who say you > can't filter tham at all - they have soft minds). > > Actually they have another limitation - forward voltage drop of around > 4.0V. This precludes their use in 3V systems (without trickery) and makes > makes current stability in 5V systems doubtful if you just use a resistor > for current limiting. You could however make a very nice torch using one of > the Linear Tech low-Vin switchmode inverter chips (running in constant > current output mode) and a 1.2V or 1.5V battery. > > Regards, > > Ken Mardle > > Applied Digital Research Ltd. Tel : +64 9 415-2514 > P.O. Box 6480 Fax : +64 9 415-3514 > Wellesley St Mobile : +64 25 879-648 > Auckland E-mail : kenmar@adr.co.nz > NEW ZEALAND WWW : http://www.he.net/~adr/ > http://www.acqura.com > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu > > -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu