Turning on an LED from 120V 60 Hz current

120(Voltage) - 2v(led volts)=118 _________ 118v ÷ 20ma(led amperage) = 5,900 ohms

Hope these aren't us answering homework assignments for someone....wouldn't be cool

120v is a the rms voltage. You need the peak to zero voltage (since an led is a diode) and assuming the Vpp/2 isn’t higher than the breakdown voltage. Usually I put a diode and a resistor in series. Meh about 5k or so. If I have a bag of leds, and I usually do, I just guess until they are as bright as I want and don’t blow up. I mean there’s a minimum forward voltage to get any light. But that usually isn’t ideal and quite dim so you want to be a bit higher. The series diode lets you use much more reasonable resistors. Remember you have to dissipate the heat from the voltage drop. Using only a resistor you would need a very large resistor (physically large- not value)

Neon lamps are actually ideal for this application - ac /mains voltage and desiring a lamp. As I’m a hobbyist- I was unaware these existed until the recent past. Same basic form factor as an led , a bit more fragile, think mini Christmas lightbulbs but much more friendly to the voltages here. I think there with 120 V it takes maybe 180 ohms. Google it don’t quote me