You can get a rough idea by taking a 5k potentiometer and put it in series with one lead. Use a 9 volt battery and do some voltage and current measurements. Set the pot to an equivalent brightens to a working light.
I use two meters like in the link below. They are plenty accurate.
I have worked at the component level in electronics since 1953.
The first 5mm LED's I worked with in 1972 were 20 ma max LED's.
Be aware that LED's are current operated devices, not voltage operated like light bulbs. The current is the important spec. You only become concerned about voltage when putting them in series. Too many in series for the available voltage and they will not light up or be very dim.
Most LED's, a 1k resistor is a good starting point.
Rich
http://www.trainelectronics.com/Meter_HF/index.htm
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
OK. Thanks for the info. All the patio lights have a single battery in them, because I have replaced some of them. I just wondered how they got away with it.
Yes, the early red LEDs were much lower voltage than today's. Different junction materials. Thise were also the days when one LED cost $5 or more, so messing up and using the wrong resistor was a costly mistake (well, when the only money I had for buying them came from cutting lawns in the neighborhood, it was). That's also why the guys who invented the blue LED wonthe Nodel Prize - blue + phosphors makes a white LED. Without blue LEDs we wouldn't have white LEDs which are now replacing all sorts of lighting everywhere.
The solar lights I had each had 3 nicad cells in them, for 3.6V. I suspect it may be more efficient to charge the cell at full power (same size solar cell array can be either higher voltage/lower amps by wiring in series, or lower voltage/higher amps wiring in parallel (or just being one large wafer). At higher current you cna get more of a charge into the battery, and a DC/DC converter is pretty efficient to step the voltage up to run the LED.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
i could have sworn that I have red LEDs from 20 years ago that operate at ~1.4V. but apparently it depends on color . See wikipedia article
greg - Philadelphia & Reading / Reading
There are some electronics inside that convert the 1.5Volts to a higher voltage pulse. Move the lit LED quickly in front of your eyes and you can see the strobe effect of the flashing.
Alan Jones in Sunny Queensland (Oz)
Is there only one battery, or two?
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
The formulas, physical and electrical properties of the materials used to produce different colors of LEDs result in different optimal operating voltages. The only way to be certain is to refer to the specs for each one. I haven't used any of the RGB ones yet. 1.5 volts sounds sort low, but may be the right voltage.
Mike Lehman
Urbana, IL
We are told that LEDs require 3 to 5 volts. But I have a half dozen solar powered LED patio lights, and they all have a 1 1/2 volt rechargable battery inside. A couple of them are color changing, and 1 1/2 volts. Any explanation on this?