# LED junk Flashlights, can I put & LED n & old school flashlight body?

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#### gary350

##### Well-Known Member
I have 11 LED lights that have all stopped working. 4 were cheep $1 lights some were$15 and $30 lights. I have 7 old school flashlights that work good but replacements lights bulbs are hard to find and people want$5 for 1 light bulb.

I have never worked with LEDs can i put & LED in an old school flashlight, It probably needs a resistor too?

I have several CREE lights that are BRIGHT, switches and circuit boards are all bad. Can i put a CREE light bulb in & old school flashlight body?

We need dependable flash lights when we go camping. It is bad to be returning from the shower after dark and the flashlight stops working. There are no street lights, even with a full moon it is dark as a cave in a forest of 50 foot tall trees. The other night returning to the camping in the dark wife has a flash light, i had a flash light and 2 spare lights. 1 by 1 they all stopped working. My back up light is a house wall switch taped to the side of an old school flash light body with wires soldered to the batteries and the light bulbs. No bad connections it always works but some day the bulb will burn out.

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#### audioguru

##### Well-Known Member
An LED needs a series resistor to limit its current. The resistor value is calculated from the spec's of the LED and from the spec's of the battery. An old fashioned light bulb is a resistor all by itself.

#### gary350

##### Well-Known Member
I put 2 AA rechargeable batteries in my old school flashlight it blew the light bulb. Alkaline batteries are 1.5 & rechargeable are 1.2v what up with that?

My LEDs are a bargan pack of 5o mixed colors? I have no clue about specs on these?

#### Tony Stewart

##### Well-Known Member
Gary LEDs are like Zeners with a Zzt knee resistance about 1/Pd in Ohms. and each colour has a unique Vthreshold and rated Vf at If.

So you know how to use zeners White being Vf=2.8V + If/Pd +/-25% roughly,.
Bargain LEDs are usually garbage and not like mine with 16,000 mcd at 30 deg. 4500K @20mA 5mm

#### gary350

##### Well-Known Member
LEDs were not invented when i graduated from college 1970. I have no clue what, Zzt, If, Vf, Pd is? I think I will put a variable resistor in series with an LED and battery then adjust it until it gets bright, then test the resistance of the variable resistor with the VOM.

#### gary350

##### Well-Known Member
OK, all LEDs are 20ma, voltage is different for each color. With 2 AA batteries = 3v and yellow LED is 1.7v so we need to drop 1.3v across the resistor. 1.3v/25ma=52 ohms.

I see no data for white or clear LEDs.?

#### ronsimpson

##### Well-Known Member
LEDs were not invented when i graduated from college 1970.
Background
Electroluminescence, the natural phenomena upon which LED technology is built was discovered in 1907 by British radio researcher and assistant to Guglielmo Marconi, Henry Joseph Round, while experimenting with silicon carbide and a cats whisker.

During the 1920s, Russian radio researcher Oleg Vladimirovich Losev was studying the phenomena of electroluminescence in the diodes used in radio sets. In 1927, he published a paper called Luminous carborundum [silicon carbide] detector and detection with crystals about his research, and while no practical LED was created at that time based on his work, his research did influence future inventors.

Years later in 1961, Robert Biard and Gary Pittman invented and patented an infrared LED for Texas instruments. This was the first LED, however, being infrared it was beyond the visible light spectrum. Humans can not see infrared light. Ironically, Baird and Pittman only accidentally invented a light emitting diode while the pair were actually attempting to invent a laser diode.

Visible LEDs
In 1962, Nick Holonyack, a consulting engineer for General Electric Company, invented the first visible light LED. It was a red LED and Holonyack had used gallium arsenide phosphide as a substrate for the diode.

Holonyack has earned the honor of being called the "Father of the light emitting diode" for his contribution to the technology. He also holds 41 patents and his other inventions include the laser diode and the first light dimmer.

(Another interesting fact about Holonyack was that he was once the student of John Bardeen, the co-inventor of the transistor.)

In 1972, electrical engineer, M George Craford invented the first yellow colored LED for the Monsanto Company using gallium arsenide phosphide in the diode. Craford also invented a red LED that was 10 times brighter than Holonyack's.

It should be noted that the Monsanto Company was the first to mass-produce visible LEDs. In 1968, Monsanto produced red LEDs used as indicators. But it was not until the 1970s that LEDs became popular when Fairchild Optoelectronics began producing low-cost LED devices (less than five cents each) for manufacturers.

In 1976, Thomas P. Pearsall invented a high-efficiency and extremely bright LED for use in fiber optics and fiber telecommunications.

Pearsall invented new semiconductor materials optimized for optical fiber transmission wavelengths.

In 1994, Shuji Nakamura invented the first blue LED using gallium nitride.

#### audioguru

##### Well-Known Member
With 2 AA batteries = 3v.
No. Two AA alkaline batteries in series produce 3.2V when new and produce 2V when they are fairly low. A 1.7V red LED is fairly dim at a current of only 0.3V/52 ohms= 6mA.

I see no data for white or clear LEDs.?
There are hundreds of LED colors/voltage lists in Google.
A white LED is a blue LED with a yellowy phosphor on top.
A clear LED is any color LED in a clear case.

#### Tony Stewart

##### Well-Known Member
LEDs were not invented when i graduated from college 1970. I have no clue what, Zzt, If, Vf, Pd is? I think I will put a variable resistor in series with an LED and battery then adjust it until it gets bright, then test the resistance of the variable resistor with the VOM.
Zeners have been around much longer than both of us and LED's behave exactly like Zeners and these are the parameters used.

Here are two LEDs 65 mW in 5 mm TH then 28x35 mm in SMD 500mW
Note the slope of VI is the ESR is inverse to Pd rating of package and thus Vf forward voltage can be predicted.

Zeners use Zzt for impedance of Zener Threshold instead of ESR and they have a wide tolerance just like LED's ( typ 25% ( which thus affects the rated Forward Voltage Vf at some rated current for DC operation..)

Thermal effects cause the Vf to reduce as well by about -4mV/'C

So ESR drops from 2.25 Ohms to 1.50 Ohms in this 500mW WHITE LED, It is a great LED due to low ESR and high brightness
That is from current rising from 30 mA to 200 mA or 600mW ( which would need a really good SMD heatsink)
4 sq. in of flat alum substrate per watt is my rule of thumb or less using a massive flashlight body.,

p.s.
Epoxy 5mm LEDs get hot inside so dont bundle them close together and drive them at 30mA and expect them to last 50kh.. They wont.

This is about 10% of the ESR in a 5mm LED which is approx 15 Ohms at 20mA

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