The left picture shows the crystal when only the top half has been exposed to white light. Ice crystals are only growing on the part that has been exposed to white light. The bottom half has only been exposed to red light. No ice crystals grow on that part. The right photograph shows the crystal after it has all been exposed to white light.
Ice crystals grow on all parts of the crystal.
The change is due to a change in surface energy caused by a redistribution of charge in the crystal caused by the light. It is also interesting to observe the colors of the ice crystals. These colors are due to the constructive interference of light reflected from the top and the bottom of the ice crystal. The color changes with the thickness of the crystal. These crystals are growing from slightly supersaturated water vapor in contact with the silver iodide surface.