If you make the object dark in color, you'll get darker photon spots. Changing the color of the transmitter object will change the color of the photons that cascade off of it. The best color for the receiver is one with a very dark ambient value, and a 50 percent diffuse value so the photons show clearly with good contrast.
More photons spilling from the lights makes for smoother shading.
Next, fine tune the light properties for Photon Emission. In the Light Property Editor, you may adjust the number of photons and the energy of each photon. Leave the number low while tuning, then turn it up to 10,000 or more for the final render. Changing the energy is more complicated. If your changes drop the photon energy too low when they strike objects you won't see the effects and you won't know what happened.