Point of use water treatment is practical with wavelengths longer than about 200 nm. 222 nm or phosphor conversion lamps have a reasonable efficiency and UV output such that they can be applied to this application.

Some phosphor powder (red and green) that is sensitive to 222 nm radiation was placed on the outside of a lamp. Note the white particles of phosphor on the table do not glow as they are not exposed to the 222 nm light in that location.


The lamp is placed into a beaker of water.


Some of the phosphor floats on the surface, but continues to fluoresce since the 222 nm radiation from the lamp travels through the water.


From the side view the phosphor can be seen glowing. 222 nm radiation is effective at killing pathogens and can be used to treat drinking water.