This is a concern for me as well. I do not install solar landscape lights because you can barely notice them. But I have came across a single spot light that has 12 LED lights in a single spot. Check out the link.
I bought some here for my solar powered street light. They are not cheap but they are high quality. I have been burning some of these in a 12volt model for over two years now, no problems at all.
They simply do not have the lumens to properly illuminate this. Depending on existing light sources around the area to be illuminated, these self powered lights just don't deliver. If the area is very dark at night, they may help a little. There are LED lighting systems which are very low power draw and put our a great deal of light. Pricey, but pay off over time. They do not have as much of an issue with voltage drop either.
There is not light at all where I put this street light and I am getting 600 lumens on a 12 volt system that stays lit all night. That is pretty good as far as I am concerned. But others may have differing conditions where LED's won't produce the desired result. You just have to know what you are looking for and what you can live with as well.
Well Amazing mine are solar but that is because I built a system to power the lights. It was not something that you could buy already made, I had to make it and collect the appropriate parts as well.
Well the bulbs I am using can be used with any type of 12V system I just happen to have one that is solar. But it can operate on anything that puts out 12V. If you check out the link I posted that company also has the same bulb that operates on 120V AC. So you can have it either way. And though they are a bit pricy the 30,000 hour expectancy of the LED's offset the cost because that bulb burned 8 hours a day will last 3750 days or 10.27 years.
12 LED Spot Light
http://www.ledlight.com/par38-ultra-bright-l...