At the time of this writing, I’ve tested 70 sunscreen formulations. Being a fun little hobby, this came as quite a surprise since I hadn’t initially believed I would have been able to acquire so many samples within such a short amount of time. Learning about the UV filtering performance of the tested formulas have been a blast, but what’s impressed me most about this journey has been with the performance of the Sunscreentester.com testing machine.

The sunscreen testing machine (combined with the documented testing methodology), is able to produce very consistent and accurate results. These results have allowed me to compare one sunscreen against another, and even produces results consistent enough to be used in determining if a brand is just relabeling a formula under a different name (See Banana Boat Sport Mineral High Endurance vs Sweat SPF 50)!

Although some people like to say, “if it ain’t broke, don’t fix it!” and though there is wisdom to that axiom, I am always looking for for ways to improve my designs. Because of this, I decided to upgrade the machine in a very important way. I discuss the changes and ideas behind them below.

Upgraded Cooling system

Concerns

Now that I’ve completed 70 sunscreen tests with a proven method and machine, I was hesitant to introduce any modifications to the system which could introduce factors which would render old results incomparable with the new. This was my primary concern when deciding whether or not to do these changes in the first place, but I believe the upgrades will allow for more precision, and better yet, the ability to increase consistency across tests by reducing the effect external temperature fluctuations has on the results.

On temperature and LED output

One of the drawbacks to using an LED as a UV source is that it is extremely sensitive to temperature fluctuations as output drops the warmer the LED gets. This means that if the ambient temperature is 85f, I may see the resultant UVI output as 13.5, vs 15.5 with an ambient temperature of 65f (cooler is more efficient). Combine this with the idea that temperature can fluctuate during the course of the 2 hour test, one may see slight fluctuations in resultant sunscreen efficacy. The fluctuations however are small enough to be considered negligible when the values are averaged (going further, if one considers the real world environment where sunscreen is used, it’s even more of a non-issue).

However, being a tinkerer and always wanting to improve, I decided to increase the precision of the machine if I can keep all else constant. My goal was to increase UVI output in order to increase testing resolution, and minimize UV output % change that ambient temperature had on UVI output. By doing so, test results should be more precise.

How does increasing UVI output increase precision?

An easy way of thinking about it is to imagine cutting an apple into 4 portions. With the 4 pieces, the apple can only be divided in 4 larger chunks. What if the apple was divided into 10 pieces instead? Because the apple is now cut into many more pieces, there is more precision in how that apple can be divided. It is this same principal where by using a higher UVI output, there will be more precision (or resolution) in calculating the % of sunscreen efficacy.

Controlling Temperature

Improved LED heat dissipation

The new heatsink uses a heatsink and fan combination which is not only more thermally conductive (using copper for the heat pipes and cooling fins), but is also much larger than the original heatsink and fan combination. The larger heatsink and fan help to reduce LED temperature fluctuations and aid in keeping the LED output steady during testing.

Temperatures can fluctuate by as much as 40f over the course of the year in my garage, so I have added a fan speed controller in order to help adjust cooling to compensate for really warm or really cool days. I am not 100% convinced this will even be needed and may just toss it out the window, but the option is always there to use it.

Do the upgrades affect the results?

Yes, but in a good way. After several tests on three sunscreen formulas (Trader Joes SPF 40 invisible gel, Cetaphil sheer mineral liquid SPF 50, and Eucerin Adv. SPF 50), the higher UVI did not affect test results for effective sunscreen (results differed by less than 1%). However, when testing a less effective formulation, the lower protection efficacy became more apparent. In my re-test of the Eucerin Adv. SPF 50 (tested 3 times), the difference in test results were 10-20% worse (with each of the test results falling within that range). This is due to the less viscous and inconsistent nature of the sunscreen, coupled with the higher UV output of the LED (thinner layer, + more UV irradiance = worse results). See results below.

Do these new readings render the previous tests incomparable?

No, because of the higher resolution, I believe the changes will provide higher precision in terms of differentiating strong vs weaker sunscreen. The previous results are still valid but slightly less precise when comparing weaker sunscreen when tested with the new cooling solution. In other words, weaker sunscreen formulations will probably test slightly lower using the new cooling solution.

How do I know which test is using which heatsink?

From this date forward (08/03/2023), I will be using the improved cooling solution to test sunscreen. The results will be shown in a table with a different coloring scheme in order to differentiate the change.

Before Upgrade

After Upgrade