Assignment

Manage what you measure

Measuring energy gives you insight into the process you are measuring, requires you to keep units straight (power vs energy; watt-hours vs watts, etc) and is helpful in comparing various processes in energy terms.

In the spirit of the class, this assignment combines the personal/local with the communal/global. For a subject you are interested in, combine direct measurements that you can make with related contextual statistics you find through research.

For example, if your interest broadly is food waste, you might measure both how much food you purchase in a week (in Calories), how much you dispose of (estimate as percentage of purchased), and the energy you use to refrigerate it (in kilowatt hours, measured by something like a Kill-A-Watt). You could compare this to food waste statistics at the city, state, country, and/or global levels, as well as fossil fuel inputs to industrial agriculture.

See the notes on measurement materials for some ideas on how to perform direct energy measurements. Make at least two direct measurements, and find at least two contextual statistics. Write up your findings in a blog post.

You should select an area of interest by week 4, when we will discuss your selection in class. We will not set aside a day to present measurement projects; however, you will be expected to share your findings and contribute to class discussions on your topic of interest throughout the semester. The written post is due by week 12, April 18.

Topic

I decided to focus my measurement project on RGB LED installations, since I love light art and how we as humans are naturally drawn to flashy lights.

There’s also been a dramatic rise in popularity of LED installations and art pieces in the last twenty years. This is likely due to their many benefits over conventional light sources like incandescent and fluorescent lights, such as variety of color and size options, energy efficiency, low power consumption, longevity, brightness, lower heat output, and less noise.

Obviously since this project is for Energy class, I’ll be focusing on the energy and power measurements of RGB LEDs specifically.

When measuring power consumption of LEDs, there are three measurements that are usually specified: maximum power consumption, black level power consumption, and standby power consumption.

An LED pixel recreates different colors by lighting up individual diodes (red, green, and blue) to different intensities. To present a full white screen, all diodes (R, G, and B) are powered to their maximum, so maximum power consumption is measured when displaying full white content at full brightness. To present a black screen, all diodes are switched off, so black level power consumption measures the power needed to run the supporting electronics (such as the controller, or drivers and receiver cards for LED walls) even when the diodes are off. Finally, standby power consumption refers to the power used when an LED display is running in standby mode, which is usually slightly lower than the black level power consumption. However, in my case I am actively mapping to my LED strips, so I won’t be measuring standby power consumption in this writeup.

Measurements

I’m also taking the Big LEDs class with Aaron Parsekian and Future Mapper with Chika Iijima this semester, both of which involve LED pixel mapping, so I’d like to combine my learnings with practical measurements from both classes.

I learned in Big LEDs that WorldSemi is the manufacturer of almost all addressable RGB LED pixels. Adafruit sells these as Neopixels.

For my LED mapping projects, I purchased this Blinkytape LED controller and this 60 LED/meter WS2812B strip. LED strips are sold in different densities, as shown below:

Unfortunately, datasheets for WS2812B aren’t very informative about the power consumption or current draw of each pixel. From the Adafruit Neopixel strip page, it states that the 60 LED/meter strip has a power consumption of 18 Watts max (~3.5 Amps @ 5V) per meter when all the LEDs are on full white and full brightness. Full white is used as the maximum rating because that means each R, G, and B LED are on at full brightness. Adafruit also states that each pixel consumes about 60mA on full white. However, Adafruit states that “usually the actual current for colorful design is about 1/3 to 1/2 the max current.”

I performed some measurements using a USB power meter (borrowed from the Energy cart) and mapping 1 meter (or 60 LEDs) on my strip using the Blinkytape controller.

VID20230418013422.mp4

References