Graphing the efficiencies of LED light strips

After adding a few LED light strips above his desk, [Bogdan] was impressed with the results. They’re bright, look awesome, and exude a hacker aesthetic. Wanting to expand his LED strip installation, [Bogdan] decided to see if these inexpensive LED strips were actually less expensive in the long run than regular incandescent bulbs. The results were surprising, and we’ve got to give [Bogdan] a hand for his testing methodology.

[Bogdan]‘s test rig consists of a 15 cm piece of the LED strip left over from his previous installation. A Taos TSL2550 ambient light sensor is installed in a light-proof box along with the LED strip, and an AVR microcontroller writes the light level from the sensor and an ADC count (to get the current draw) of the rig every 6 hours.

After 700 hours, [Bogdan]‘s testing rig shows some surprising results. The light level has decreased about 12%, meaning the efficiency of his LED strip is decreasing. As for projecting when his LEDs will reach the end of their useful life, [Bogdan] predicts after 2200 hours (about 3 months), the LED strip will have dropped to 70% of their original brightness.

Comparing his LED strip against traditional incandescent bulbs – including the price paid for the LED strip, the cost of powering both the bulb and the strip, the cost of the power supply, and the time involved in changing out a LED strip, [Bogdan] calculates it will take 2800 hours before cheap LEDs are a cost-effective replacement for bulbs. With a useful life 600 hours less than that, [Bogdan] figures replacing your workshop lighting with LED strips – inexpensive though they are – isn’t an efficient way to spend money.

Of course with any study in the efficiency of new technology there are bound to be some conflating factors. We’re thinking [Bogdan] did a pretty good job at gauging the efficiency of LED strips here, but we would like to see some data from some more expensive and hopefully more efficient LED strips.

Reviewing the numbers from one month of solar harvesting

[Mathieu] just finished analyzing the numbers from a month of solar energy harvesting. You may remember that he was curious to see what kind of energy can be collected from small solar cells used indoors. He built several copies of a test platform which collected data between December 16th and January 16th.

First of all, it’s not shocking to find out that rooms with no sunlight produced negligible energy during that time. When you think about it, if they had been gathering a statistically significant amount wouldn’t that mean the lighting used in those rooms was incredibly inefficient? In other words, there’s no way you need to be making that much light.

But he did find that proper positioning in rooms that catch sunlight during the day can result in usable energy for small loads. He established that a 0.5 Watt panel harvested just a bit more than half of what a 1 Watt panel did. But perhaps the most useful discovery was that it’s quite a bit more efficient to have a charging circuit store energy in a battery rather than directly powering a fixed load.

It will take us a few more viewings to really decide what we can take away from the experiment for our own projects. But we appreciate [Mathieu's] quest for knowledge and his decision to put this information out there so that others can learn from it.

Getting the lead out of the Arduino runtime

mhvlib_arduino_efficiency_runtime

Ah, the Arduino.

Love it or hate it, there’s no denying that part of its accessibility comes at the expense of speed and efficiency. We honestly like the platform as well as all of the others out there, because we believe that everything has its proper place and purpose. The crew over at Make, Hack, Void think that the Arduino dev boards are well and good, but that the core of the Arduino runtime could use some improvement.

They have taken it upon themselves to dig deep into the code and make some of the improvements that many advanced Arduino users have been clamoring for. Their MHVLib is an efficiency oriented runtime library which works on all AVR microcontrollers, whether they be standalone uCs or Arduino-branded hardware.

They have changed the way that the Arduino handles pin and port information, as well as how object and buffers are allocated in memory. Their code still relies on an Arduino-style bootloader, though they recommend Optiboot since it’s about a quarter of the size of the Arduino version.

There’s a complete list of what has been implemented available on their site, and you can grab the code via their GIT repository if you want to give it a try yourself.

Cheap hack may double solar panel power

MIT researchers have devised something they call the Solar Concentrator which is to be placed on top of existing solar cells. Its purpose is to separate the visible and infrared spectra of light by absorbing the visible spectrum and routing the energy to specialized cells. They claim this could lead to doubling the panel’s efficiency and greatly reducing costs.

We have seen many promising advances to solar panel efficiency in the past few years, but what is special about this one is the amazingly simple and cheap technique. Essentially, all the team has done is coat a piece of glass with simple organic dyes. After the organic molecules absorb the visible light, they remit the energy to the sides of the glass where it can be routed to their specific cells. The process is more efficient because the dye absorbs the light rather than something expensive like silicon. That means less silicon, and thus a better price range. Also, the fact that this material is just a piece of glass also opens up the possibility of solar windows.