A schematic of a Lambda field generator
A Lambda field generator was a piece of equipment used in conjunction with a Krieger wave converter to produce Krieger waves.
Doctor Nel Apgar used a 23 megawatt low frequency lambda field generator for his experiments with Krieger waves. The generator (located on the surface of Tanuga IV) produced harmless Lambda field energy pulses that were reflected by the converter on Dr Apgar's space station in orbit of the planet. The generator was placed on the planet's surface as it requires a minimum of five-thousand kilometres for the field to produce parallel rays of light. The generator inadvertently caused the facsimile of a Krieger wave converter created on the holodeck of the USS Enterprise-D to produce Krieger waves, resulting in radiation bursts on the ship. (TNG: "A Matter of Perspective")