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Discussion Starter #1
I'm trying to figure out what LED I could use to replace an incandescent bulb with and get about the same brightness? For example, if I have a 12v 80ma bulb, what would the equivalent be for an LED? Is there a way to do this?
 

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The 3 to 5 Volt "Bright white" LEDs put out lots of brightness when viewed looking at the rounded end. Can actually be painful to the eye at times. BUT, the general lighting effect is not the same as an incandescent bulb.

LEDs typically draw only 20-milliAmps.


First, the majority of the light come out the rounded end and little out the sides so some sort of diffuser is needed to disperse the light around.

Second, the frequencies of the light are in very narrow bands and although they are white and are very bright to the eye looking directly "AT" them, the light that shines on other objects to be reflected back to the eye seems to be very dim. I have several LED flashlights that have from one to 47 LEDs in them and looking right at them is difficult and quite painful, but using them to illuminate a work area is near useless... even the 47 bulb flashlight I have just does not provide enough light to do any useful work, in my opinion... better than no light at all if stumbling around in the dark when a fuse in the house is blown, but not good enough to look for the fuse that fell on the floor while changing it!

If your power supply is 12-Volts, you can put 4 LEDS in series to account for the supply voltage or you can put a resistor in series with just one LED. The resistor should be about 450-Ohms (+/-20%) for 1 LED on a 12-Volt supply. There are also LEDs that have the resistor built-in... check the specs of the LEDs you get/have.
 

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Lumens is the way to measure brightness, but what you asked is basically "what led is the same brightness as an incandescent".

Charles has it down, it's not even as simple as measuring it with a meter. The dispersion of the light is all different. Basically, if you want it to be really bright, look for the "super bright" LEDs, or if possible, use multiple LEDs.

Regards, Greg
 

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I have "Warm Yellow" LEDs in stock, if anyone is interested. If you want to shop around on your own, look for those in the 5500mcd range. They give out plenty of light, but no where near that of the super bright LEDs. I think mine look good as a loco headlamp. What is your application for the LED?
 

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Discussion Starter #6
I'm looking at making some signals. Do you have color LEDs, red, green, amber?
 

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Since the best/brightest led's from the Shack need to be ordered, go to Allied Electronics, newark, digikey, jameson , etc for led's.

there are 3 and 5 mm bright led's available and in many different brightness and colors.

These places will also have 1/2 and 1 watt resistors for limiting the led current.

Remember that a 3 volt led at 20 milliamps on 24 volts needs to have 21 volts dropped resulting in almost .5 watts. A 1 watt resistor should be used here.
general rule for resistors is to use double the wattage needed to keep the resistor cool (read: will not melt plastic).
 
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