Friday, December 24, 2021

K2GOG EOY 2021 Loose Ends #1: Charting Work Bench Lighting

While at the Fair Lawn Amateur Radio Club (FLARC) hamfest back on June 5th 2021, I acquired some 4 foot long LED lighting strips that were part of some type of dismantled commercial display.  

The seller of these usually brings some "scrap" material from his day job and this was not the first time I bought something from this person, whose name escapes me at the moment.

It took until October to find a use for one of these LED strips after realizing that I needed a little more light than my two ring lights can offer while doing work bench videos that I did not want any shadows on.

K2GOG small project bench lit up with only the LED strip under the support shelf 
(Source: Steve Bossert K2GOG)

K2GOG small project bench showing the LED panel installed under the shelf.
(Source: Steve Bossert K2GOG)

Now with three sources of light on my "only small projects" work bench, I figured it would be handy to measure how much light is cast by this new under shelf fixture.

K2GOG 2021 Loose Ends:  Measuring Lux

Fast forward until the last days of 2021 when I have some spare time to knock out a few random projects.

A benefit of using a variable voltage bench supply with a serial output means I can do some nice real world data visualization with a practical purpose. 

Additionally, I also used a multimeter that can measure voltage, current and lux but not all at the same time for this article.

Sigrok is a very good open source application if you have a bench supply, oscilloscope, multimeter or other test equipment that you want to combine with your computer for data capture or logging if it can export its reading via a serial connection.

Scientific Process Commence! 

In chart 1 below you can see on the Y axis, the current draw and on the X axis, the voltage in 0.5 increments required by the LED strip.

Once I hit about 7 to 7.5 volts, the LED strip became dimly lit and its current draw is almost logarithmic as I increased voltage, but with a few fluctuations if you look closely as I stepped through the measurement process.

Had I run this test setup at maybe 0.1 or 0.2 volts per step, it may have been a little more accurate but had I run the test at 1 volt steps, a good bit of data would not have been shown. 

All I  really wanted to find was the "sweet spot" for voltage and current via a dedicated full time power source for the optimal level of light. And I found that easily after looking at this chart I created! 

Chart 1 - Y axis = current and X axix = voltage
(Source:  Steve Bossert K2GOG via Sigrok and a supported power supply) 

Past 20 volts, the current continued to climb but there was no benefit to moving past that point from the perspective of light output so is why the chart stops at 20 volts. The heatsink on the LED strip certainly got warm to the touch when drawing more than 3 amps too! 

We have the light!

Looking at the below chart 2, the X axis again shows voltage in 0.5 steps and the Y axis now shows approximate lux (lx) as measured by the ambient light sensor compatible with one of my Sigrok compatible multimeters.  

Please note the lux sensor stayed at a fixed location 14 inches below the center of the LED strip for all voltage comparison measurements. I am also not endorsing the accuracy of these lux measurements as all I needed were relative approximate lux measurements and not something that was lab grade accurate.

Chart 2 - Y axis = lux and X axix = voltage
(Source:  Steve Bossert K2GOG via Sigrok and a supported DMM)

As charted above, going past 16.5 volts does not give much benefit in terms of light output compared to the additional current draw.

And now the solution

So for a dedicated full time power supply, I will re-purpose an old laptop supply rated at 3 amps at 19 volts along with a pair of step down converters to give me a high and low light capability.

The high setting provides 16 volts and the low setting is set for 10 volts which gives me roughly 3x difference in light output.

Hope you enjoyed this loose end and to inspire you to try something like this.  And, if you were wondering, I kept some details like which power supply, multimeter, step down converters, etc out of this article on purpose so you can do some of your own research and to not promote specific vendors.

Happy Holidays! ~7 more days until 2022!

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