Ben's Website

Serious musings

LED Christmas Lights

For any given product, it is always interesting to see which aspects are improved and which languish.  Engadget's recommendation of the best LED and incandescent Christmas lights highlighted this; the difference between the LED and incandescent strands is almost entirely restricted to the bulb (and associated electronic driver).

LED Christmas light (top) versus incandescent (bottom)

Looking carefully at the above picture, the incandescent bulb can be removed from the socket while the continuous mold line (lying exactly between the socket's two flat sides) suggests that the LED bulb cannot be removed.  Assuming this, I'd wager that the LED bulb is first connected to the wires and then the socket molded around this connection.  The socket length and design, then, serve no functional purpose beyond fulfilling the consumer's expectation.

LED Christmas lights were just coming to the market during my senior year in high school.  My senior project focused on the attachment of the bulb to the wire, where I realized that the increase in bulb quality (incandescent to LED) and associated decrease in bulb failure lessened the need for consumer-replaceable bulbs.  So, I designed a light strand where the LEDs were directly inserted into the wire and also a machine to construct these strands.

LEDs can be inserted directly into the wire, then encapsulated in plastic/rubber for electrical isolation.

Removing the socket results in a more compact light strand which should be cheaper to produce (less material and elimination of a dedicated electrical assembly) and less visually-intrusive because the 'socket' has been substantially reduced (Christmas light strands are green to blend in with the tree).  Electrical contact is maintained without soldering by the compliance of the wire, much as a nail driven into wood is retained by forces from the compressed fibers.

A simple machine to make LED Christmas lights. From left; a spool of multistrand, multiconductor wire passes between two vertical-alignment rollers, through a wire-puller (drive), and into the LED inserter. LEDs fall from the vertical hopper into a bit and are driven by the pneumatic cylinder into the wire, such that their leads pierce the wire, making electrical contact. Exiting the wire, the leads are bent against the wire in the same manner as a stapler curls the staple on the back of the paper. This prototype does not encase the LEDs; after the press the light strand is wound around a spool for packaging.

I've learned much in the eleven years since this project, but this idea remains relevant and would be fun to revisit.  I built this project in the context of the Szmanda science scholarship, so my paper and presentation highlight the energy efficiency of LED lights against traditional incandescents. (The presentation's pictures tell a great story.)