There's a lot of hands-on evaluation that goes into this product category. One of the main reasons for that is the bulbs themselves. It's difficult, if not impossible, to use a product's specs or photos to get a feel for how durable you can expect the bulbs to be. Sometimes you'll get lucky with a "shatterproof" notation in the description, but not always.
Another bulb aspect to consider is the physical connection. Some of these come preinstalled and you can't replace them yourself. Some are preinstalled and can be removed. Most bulbs, in my experience, come packaged separately for you to install yourself. Most of the time, that isn't a problem. Occasionally, since these products all attempt to have a waterproof seal, the bulbs can be difficult to install. A couple of times I found myself gripping and twisting the small bulbs hard enough that I was concerned they might shatter in my hands. None did, but it might be worthwhile to have a pair of gloves on hand if you find yourself in the same situation.
Overall, the main concern with most lights is how much light they put out. In the past, for some of our standard light bulb testing, we've used an integrating sphere. That type of equipment can get you a ton of information for a light source, including brightness in lumens, color rendering index and more. Read more about our light bulb test lab.
For this category, I was specifically interested in brightness. Unfortunately, these string lights can't be tested in our integrating sphere, but with some fancy math wizardry, I changed the calculations we needed from a sphere to a linear path and came up with a workable solution. Using a standard digital light meter, I was able to get an approximation of each bulb's light output in lumens.
Looking at the chart above, you can see the brightness of one individual bulb from each strand, as well as the total brightness of the entire strand from the solar and battery-powered options. The Real Living bulbs were dim. Hampton Bay has the brightest individual bulb, while Coleman says the brightest strand in this series overall because of a higher bulb count.
In the AC-powered options shown below, Brightech carries the brightest individual bulb at about 196 lumens. Multiply that by 15 bulbs and you nearly hit 3,000 lumens. Magitec wins brightest overall with 30 bulbs at 165 lumens, for a total of almost 5,000 lumens. To be fair, Magitec offers two strands for the price of one, so one individual strand would be about 2,500 lumens; about 500 less than a single Brightech strand.