Lux Conversion

Bring in the efficiency of the light source in lumens per watt, and the distance to the illuminated surface, considering a spherical surface at that radius.

As I read the definition of lux, it relates to the illuminance as perceived by the human eye. Since the lower limit of human vision is around 400nm, your wavelength of 254nm is way too short for the human eye to perceive, and the luxmeter should not respond to it, other than to indicate danger!

If your luxmeter is really measuring radiation of that wavelength, then perhaps it is missing an ultraviolet filter.

If there is indeed significant radiation at that wavelength, then you need eye protection to enter that area! The most painful thing I have ever experienced was eye damage from excessive exposure to ultraviolet light!

The lumens/ watt capacity of all the lighting sources are different.

Visible light is between 400nanometers to 700 nanometers.The one mentioned by you lies in ultaviolet region and is harmful wavelength and should not be produced in open places.

normally Halogen lamps may give you max 14 l /watt

Light emmiting diods 100l / w

however lux level will depend up on application area