It's hard to believe now but there was a time back in the early days of the Silver-Age that Green Lanterns didn't create anything they could imagine using only Will and an innocuous looking decorative bauble. Back then power rings deployed a solitary green beam possessing all manner of wondrous properties which were often very different to the abilities we are familiar with today.
I was amused to stumble across this panel in a reproduction of Green Lantern #6 (vol.2), 1961, showing an incapacitated Hal Jordan on the plant Aku . He must complete his mission to rescue the local populace from the snares of tyrannical doppelgangers and so he conjures up a perfect double of himself using his ring's energy.
The editor, credited as Julius Schwartz, is careful to point out that creating an image "out of thin air" is something we should not expect a Green Lantern to be capable of under normal circumstances. It is only thanks to the unique properties of the "super-magnetic field" of the planet Aku that we are able to witness such an extraordinary feat here.
I wonder what old Julie along with writer John Broome and penciller Gil Kane would say if they knew that, in a future version of the mythos they'd pioneered, making constructs would be the first thing that every new recruit to the Green Lantern Corps would learn at rookie school?