
And here is a side by side shot.

From the above shot, we can see that they put out the same amount of light. From the side by side, we can see that they are shaded lightly on the sides. This makes them darker looking, especially the large block because there is more surface on the sides to make it noticable. I tried with a completely white (255,255,255) color and the shades are still there. If you want the complete white texture, it is here -->
<--. Just right click it and save image as and save it with the name lightsplus_light.png in your minetest\textures\all folder and it will override the original texture. Or you could just save it in your minetest\mods\newlights\textures folder and overwrite the original texture. But it wont help you much.