My estimated lumens numbers (based on 50 lumens per watt) were pretty darn close to the ones from the manufacturer.
Consumer LED lighting products tend to be in the 40-80 lumens/watt range.
There is some even higher performing stuff, but it is even more expensive. Not something you’re going to find in a $20-$30 solar fixture. You’ll find $10 worth of LED chips and another few bucks’ worth of driver electronics in a $100 retail 4-5W Kichler fixture. Which frankly puts good LED fixtures outside the price range of most people and I recommend they go with halogen instead. You can always get back into LED via the lamp, e.g. using an MR16 spot for which there are MR16 LED bulbs. Prices will come down over time.
At any rate, when the light output is off by a factor of 5 to 10, the last factor of 25-33% based on actual lumens/W efficiency is immaterial.
It takes some thought to do a nice job lighting your yard. I spent a few hours researching, and then did some fun things, like a pair of carefully aimed waterproof well lights illuminating a trio of birch trees in front of our house in light and shadow. It’s a dynamite effect, really breathtaking and makes the trees pop. You can’t see the lights unless you literally walk into the yard and go behind the trees, which is how it should be. A couple fruit trees are moonlighted, which is where you hang a fixture in a tree and then light filters down and out from its branches. A stand of bamboo is dramatically uplit. A couple of large bushes in back on a major sight line have small well floods. My path lights tend to be at critical, otherwise dark and important places like gates and steps. If they weren’t there, you’d fumble. With them there, you can see. Each one has a purpose. When we sell our house some day, I am confident we will get at least 3 times back on that lighting investment what I put in.
You can’t do ANY of those things with these lights.
When I go walking by a house with a set of these cheesy solar lights, laid out alongside their front walkway and there’s more light on the walk from the street lamp and their porch light than from the lights along the walk and I gotta wonder how much that person thinks about how their house looks. I know what I’m thinking - throw the dumb little things in the e-waste bin.