What do you look for in far-UVC UVGI? 254nm UVC or 222nm far-UVGI?

The latest (actually not so new technology) is the 222nm far-UVC.
Typical wattage: 500w
Approximate length: 600mm
Expected life: 30,000 hours warranty

Important to have hour run meter.

222nm far-UVC lamps are recyclable and replaceable with no mercury.

• Lamp does not contain mercury or other dangerous materials.

• Rugged construction withstands harsh HVAC environments.
• Reduces wear and tear, extends the life of HVAC systems.
• Clears HVAC coils of mold and all other bio-growth.
• Single-pass kill of 99.99% in 1/5 of a second.
• Not affected by temperature or humidity.
• Engineered so as not to produce ozone.
• There are no electrodes to wear out.
• Minimizes maintenance costs.
• Power level is adjustable.

Note: 222nm has a human exposure limit of 25mj/cm and 254nm UVC limit is 6mj/cm2. Far-UVC is perceived to be safer but safety precaution is still mandatory.

The degree of pathogen inactivation by ultraviolet radiation is directly related to the UV dose applied. The UV dose is the product of UV intensity [I] (expressed as energy per unit surface area) and exposure time [T], 

therefore: 

DOSE = I x T, commonly expressed as millijoule per square centimetre (mJ/cm2).