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At this point, we’ve created a simple circuit with a single LED on a solderless breadboard. A single LED doesn’t have enough luminance to light up a jack-o-lantern as well as a candle can.
Fortunately, adding additional LEDs is easy!
Schematic for an LED Pumpkin Candle with three LEDs.
Even though this LED schematic includes three LEDs, it doesn’t use more power than the single LED circuit!
The same electrical current that passes through the red LED is passing through the yellow LED and green LED on its way back to the battery. In fact, because some additional portion of the battery power is being converted into light by the extra LEDs, the three-LED circuit runs slightly cooler than the single-LED circuit.
To compensate for the extra LEDs, the resistor value has been reduced from 470 ohms to 220 ohms. If the resistance had not been changed, the LEDs would still have lit up, but the LEDs wouldn’t have been as bright.
Three LEDs on a solderless breadboard.
When creating this circuit on a solderless breadboard, notice that the wires shift over one column between the red LED and the green LED. If your yellow LED doesn’t light up, you’ve accidentally plugged all of the wires into the same column.
If none of the LEDs light up, then you have installed one or more LED(s) backwards. You can play around with guessing as to which LED is backwards, or you can keep a separate breadboard with the single-LED circuit to test the orientation of each LED.
The three-LED circuit has one important limitation worth noting: Unlike the single-LED circuit, the three LEDs can no longer be any color you want. The three-LED circuit can only use the red-to-green portion of the rainbow.
However, you can mix and match those colors. For example, you can have a red, yellow, and green LED. Or, you can use three red LEDs. Or, three orange LEDs. And so on.
But, you cannot reliably use aqua LEDs, blue LEDs, white LEDs, purple LEDs, or ultraviolet LEDs in the three-LED circuit. Each of those colored LEDs requires a high enough voltage (between 2.8V and 3.7V) that it is not possible to add three together and supply enough power from a partially-exhausted 9V alkaline battery or even a fresh rechargeable battery, such as a Ni-MH battery or rechargeable NiCad battery pack.
A 9V battery can’t fully power three white LEDs in series over the full life of the battery. A fresh 9V alkaline battery might power them for a short time, but they’d grow dim quickly.
However, a 9V battery can power two LEDs:
Schematic for an LED Pumpkin Candle with two LEDs (white or ranging from blue to ultraviolet).
Notice the specified resistor has changed values yet again. This time, the resistance has been dropped to 180 ohms to compensate for the extra voltage that these colored LEDs require. If the resistor had stayed at 220 ohms, the color LEDs would not have been as bright. If the resistor had stayed at 470 ohms, the color LEDs would have been even dimmer.
A blue LED and white LED on a solderless breadboard.
Two 5mm LEDs are easier to implement on a solderless breadboard than three 5mm LEDs. The resistor and LED wires are all in the same column.
But, only two or three LEDs are still not going to be enough to light up a pumpkin!
To add additional LEDs, simply add additional strands of two or three LEDs parallel to the first series. You’ve finally made it to the LED schematic that will be used to create replacement pumpkin candles.
Schematic for a complete LED Pumpkin Candle with numerous parallel strands of LEDs.
You can add up to five parallel strands of three LEDs and still be within the project’s temperature and power consumption limits. A fresh alkaline 9V battery will last over 5 hours with five strands.
LED Pumpkin Candle on a solderless breadboard with two parallel strands of LEDs.
Electrically speaking, you can mix and match different colored LED strands. That is, you can have a strand of two blue LEDs, followed by three red LEDs, followed by a orange/green/red strand, followed by a strand of two purple LEDs.
Visually speaking, mixing colors tends to result in a homogenous mess, rather than a stained-glass window effect. But, that’s why you have a nice solderless prototyping board: to experiment!
We’re ready to light up a pumpkin...
