There are many ways you can many your lucid dreams brighter, you just have to be creative! They're your dreams, therefore, you can bend them to your will. You can try something as simple as a voice command, starting off with stabilizing, "stabilise!" and then perhaps increasing the vividness/clarity of the dream. Finally, use something like "brighten". If that doesn't help, you may just have to turn on a light or.. summon a sun A pair of night vision goggles, maybe?
What you can do is endless, just use your imagination~