LED mounted in a contact lens for possible virtual / augmented reality displays

Every so often, internet news aggregator sites run a story about a research group that put an LED into a contact lens, then inserted it into a rabbit's eye. I figured that I would try the same thing, but put the lens into my own eye. I accomplished this by laminating a coil of wire and an 0402 surface-mount LED between two ordinary soft contact lenses. I was hoping the lenses would stick to each other, but they did not, so I ended up fixing the edges together by pinching the plastic together with hot tweezers. This held well enough to capture a minute of video with the LED illuminated in my eye. For video purposes, I mounted the LED facing outward. An actual VR/AR display would have the LED facing inward.

I powered the LED by using a very primitive spark-gap transmitter built from a mechanical relay to send RF energy into a larger coil held near my eye. The large coil coupled the energy into the contact lens coil and pulsed the LED.

http://nextbigfuture.com/2011/11/single-pixel-contact-lens-display.html


http://www.cs.uic.edu/~kenyon/Papers/Soft%20Contact%20Search%20Coil.Vision%20Research.Kenyon.pdf

Tutorial: Electrical impedance made easy - Part 1

This is the first video of a short series in which I discuss the basics of electrical impedance from a practical standpoint.

In this video, I show how a simple LED power supply circuit can be made more efficient by replacing a resistor with a capacitor. I describe the difference between resistance, reactance, and impedance.

Shop lighting upgrade: T5 vs T8 fluorescent vs LED

I am in the process of upgrading the lighting in my shop. It currently has a number of 4-lamp and 2-lamp T12 4-foot fluorescent fixtures. The best solution is to replace the ballast in each of these fixtures with high-efficiency electronic ballast ($15), and replace the lamps with T8 high-CRI bulbs. This will save energy, and greatly improve the quality of the light. LEDs and T5 fluorescent are MUCH more expensive to install, and their energy savings are not nearly enough to justify the cost. Most LED systems actually use more energy than T5 or T8. Remember that running a T8 with an electronic ballast will provide more light than it's nominal rating, which is for magnetic ballasts. T5 are always rated for electronic ballasts, so it is not a fair comparison.

For new fixtures in my shop, the cheapest/best solution is to buy $10 "shop lights" and replace the ballast. The total fixture cost is $25, and efficiency is 96 lumens/watt for a total output of almost 6000 lumens. It can't be beat! Commercially-available T8 fixtures with electronic ballasts are more expensive, and the quality of the ballast is suspect.