Table of Contents
For this experiment, I headed to CNET’s Product Test Lab in Louisville, Kentucky. There, using a reflectometer and a little basic physics, I assessed the machines’ performance, comparing their cleaning efficiency against the most common substances that stain carpets.
Colour
As you may remember from high school physics, color is simply our brain’s interpretation of visible light of different wavelengths. For example, red corresponds to long, low-energy wavelengths around 700 nanometers, while blue and violet represent short, high-energy wavelengths, with violet having the shortest of these wavelengths at only 380 nm.
The electromagnetic spectrum. Our eyes can only see the part in the middle. We call that visible light.
When we look at a red apple, two things happen simultaneously; the skin of the apple reflects only the long wavelength (red) light and absorbs most of the other light. Our eyes collect this information and immediately send it to the brain for processing. This is how we can perceive color (red, in this case) with astonishing precision. You may be wondering why black and white are not part of the image above. That is because white includes visible light of all wavelengths together, while black is the absence of visible light.
That’s all well and good, but how does any of this relate to testing carpet cleaners? Glad you asked.
Carpet Cleaning Efficiency Test
Our eyes can see the difference between a dirty and a clean carpet, but how do we actually see this? measuring unit that difference? In theory, if we could quantify the light reflected by a carpet sample (i.e., to measure its “color”), we could judge the cleaning power of each machine by taking color measurements of a brand-new piece of carpet and comparing them to measurements obtained after it had been stained and then cleaned. The ratio of these two reflectivity values (before vs. after) would allow us to judge performanceIn my testing logic, the more similar the numbers are, the better the carpet has been restored to its original color. We can repeat this procedure for each UUT (unit under test) and compare the results… Yes, that’s exactly what we did.
Photovolt 5700PC Reflectometer and Search Unit. The search unit contains a tristimulus filter that prevents other types of light (e.g. UV and IR) from interfering with the measurements, and a photosensor that measures the amount of light reflected from the surface of the test subject — our white carpet.
Meet the reflectometer, a device with many color matching applications in industries such as textiles and paint. Fortunately, the operating principle of the reflectometer also applies to our purposes. Our Photovolt Model 577PC Reflectometer has a search unit or “probe” that houses a tungsten lamp that emits light in all directions within a chamber and then measures how much of that light is reflected back to its photosensors. This measurement generates a voltage that is linearly correlated with the amount of reflected light seen by the photosensor, allowing us to quantify light and color. Science.
We use the Whiteness Index as a frame of reference. This parameter is used to measure how “white” a sample is by measuring its reflectance under two different light filters (blue and green) and then using an equation to correlate and normalize these values. Since we are using a white carpet for this test, by obtaining before and after WI values we get an accurate representation of how much dirt and stains were effectively removed from our carpet by each machine.
We segmented four 6″ x 6″ “spot squares” each with one type of soil. We placed the search unit on top of the brand new white carpet sample and measured its WI. To ensure repeatability and accuracy, we took five measurements at different locations in our soil square and averaged the reflectance measurements.
We have selected four fabrics for the coloring:
- 150 ml sweet red wine: A sugary, alcoholic substance with a proven stain-removing effect.
- 150 ml Black Coffee: An acidic, everyday substance that contains tannin, a naturally occurring colorant.
- 150ml Motor Oil: Our favourite oil stain. Difficult to remove as it does not mix well with the water released by the UUT.
- 60g marinara sauce: an organic substance made from tomatoes. This stain proved to be the hardest to remove.
Staining the carpet with sweet red wine, coffee, motor oil and marinara sauce.
We proceeded to soil the square sections, allowing the contaminants to settle for about an hour. We then began the cleaning process. Two cleaning cycles were performed on each colored square. A cleaning cycle consists of two wet passes followed by four dry passes. Finally, we measured the reflectivity values at the same five locations as before and took the average. The ratio of the final versus initial WI values tells us how efficient the carpet cleaner was in restoring the carpet to its original white.
Example of a stained carpet before and after it has been cleaned by a carpet cleaning machine. Note that in all cases the dirt was not efficiently removed from the carpet… Can you guess which unit this is? (Hint: it’s not one of the top three choices above.)
The heavy junk test
Our lab technician, Eric Snyder, carefully measures marinara sauce for the tough-to-get-on test.
Marinara sauce was the hardest type of dirt to remove. Since every cleaner had such a hard time getting it out of the carpet in just two passes, we thought it deserved its own category. Hence the heavy-duty mess test.
For this challenge, we followed the manufacturers’ recommendations to set each cleaner to the “max” or “tough mess” setting and performed any additional cleaning steps such as pre-treating with a supplied chemical, pre-treating and steam cleaning, etc. We modified the WI equation to be more suitable for comparison and performed the same procedure for taking color measurements and comparing the WI values.
Marinara stains are a stubborn, tomato-y mess.
Results
Let’s keep in mind that the test is designed to be harsh. To ensure comparability, the units were only allowed to be cleaned in a limited and controlled manner. More importantly, the WI comparison assumes that the sample under the reflectometer is pretty close to true white. White printer paper is 91% white, while our carpet is 55% white. It’s the whitest carpet we could find, but it’s not That white. Don’t be surprised if the scores seem low overall.
Here’s a fun fact: During this experiment we had a total 700 measurements, all to give you the right information to make an informed purchase decision that suits your needs. The table below summarizes the results, and remember, higher scores are better.
The results are in. See how different models compare in terms of cleaning performance (the higher the score, the better).
Other carpet cleaners we tested
Bissell Hydrosteam Pet Model 3423: I had high hopes for this model, as it is one of the more expensive models, but it only managed to score the third lowest in our heavy-duty mess test. Despite using steam delivery technology to pre-treat and clean carpets, we were not impressed with its performance.
Bissell ProHeat 2X Revolution Pet Pro Model 3587: This unit scored surprisingly high in our tough mess test, coming in third in that category with a respectable score of 66.1. It didn’t score as high when it came to cleaning other types of stains, finishing with the third-lowest cleaning score overall in our tests. It does come with a two-in-one furniture tool, a three-in-one stair tool, a 3-inch deep stain tool, and a very handy cleaning drawer for the unit, but we think there are better options out there.
Hoover Pro Clean Pet Carpet Cleaner: One of the least expensive models in the group, but its performance wasn’t all that great. For starters, this Hoover cleaner was the only unit to receive a “fail” rating in our test. In the case of marinara and motor oil, it even seemed to spread dirt along its path across the carpet, which is never a good thing.
Bissell Crosswave Hydrosteam All-In-One Multi-Function Cleaner 3515 Worst performer in both our cleaning efficiency test and our heavy mess test. It was very difficult to push this unit over our low pile carpet, probably because the cleaning brush roll was stopped by friction against the carpet fibers. Highlights of this product include its steam output capacity and that it can be used to clean other surfaces such as hardwood floors.
