The direction of your solar panel will make a massive difference in how bright its light will be at night. As solar panels require large amounts of sun exposure to power the light, the more exposure they get, the longer and brighter they will shine.
The efficiency of charging and therefore extended brightness is enhanced with the best direction of light into the panel. A reflector can be created from aluminum foil or even anything painted white paint. The bigger the surface area of reflector, the better as long as it points the light into the panel.
The solar panels found on higher-quality lights will also tend to use premium photovoltaic cells. These will absorb more sunlight and can even generate more battery power for your solar lights in general. A premium light manufacturer tends to squeeze out more from their lights than cheaper variants.
If you find that your solar lights are not as bright as they used to be, try changing the angle of the solar panel. Sometimes a slight adjustment can make all the difference.
To make solar lights shine longer, position panels where they soak up 6-8 hours of sunlight daily. Dust them often for better energy absorption. Place lights in sunny spots, away from shadows or artificial light. Charge batteries fully initially for 12-14 hours. Keep panels clean for efficient charging.
If your panel is on a dark wall which soaks up the precious commodity of light the most, consider adding a reflector around it that bounces the light back towards the panel. Think about channeling light into the panel as if it is like adding fuel to a car. Spraying gas all over the car will see very little go into the tank, so it is with light too.