The stock P3D landing and taxi lights seem very weak to me. I found a solution on the P3D forums that I'd like to share here. The lights are now significantly stronger and more realistic.
Make a backup copy of the fx_landing.fx file located in the Prepar3D Effects folder.
Open the fx_landing.fx file using notepad or some other text editor.
Find the [ParticleAttributes.0] section.
Change the Falloff Exponent value to something between 1 and 2. I set mine at 1.5.
You'll have to reload the sim to see changes.
Done