# LED Christmas lights without limiting resistor

My LED Christmas light strings do not have a series limiting resistor, how is this achieved? They are 70 LED strings with two 35 bulb sections. I have carefully checked and there are no provisions in the plug or inline with the wire. I measured resistance from sockets back to plug and measured no impedance. What am I missing? Can the the LEDS be made (doped) so the internal resistance be high enough that as a group they provide sufficient impedance?

• These lights typically have a power supply for them ...that in all probability will be a CC supply so does not need any series resistance in the LEDs.. – Jack Creasey Oct 20 '18 at 16:05
• These are 120 Vac plug in lights, no separate power supply. I have used infrared thermometer and saw no heat rise in sockets or plug. – D. Elttub Oct 21 '18 at 21:07

In the 220V set he found 3 resistors in 3 of the LED bases, the rest had no resistor. Each resistor was 510R for a total of 1530$$\\Omega\$$. He also says he found a bridge rectifier molded into the bit where the wires split.