I had thought of this (idle) query a while ago and promptly forgot it, until just now when a thread on bizarre (zero-radiation emitting) nukes was OP’d.
Could you design nukes incredibly wrong-headedly, to produce the most radiation in the visible spectrum, forgetting about blast and other radiation goals, to achieve the most “amount” of light old Terra has ever seen not coming from space?
You want a new Sun? Let’s set one up. Blinding everybody is not an issue.
Not sure how to formulate this to distinguish from other energy measures/results, such as short bursts of intense light (in inertial confinement experiments?) that we already are producing.
The fusion reaction in thermonuclear weapons produces gamma rays and neutrons. All of the visible radiation you see is from secondary absorption of gamma rays by the cloud of bomb materials and the atmosphere which produces gas heated to incandescence. The resulting temperature is what drives the spectrum. There is no specific limit to how much yield you could get from a multistage thermonuclear weapon, although at some point it will not be possible to get effective containment and the weapon will blow itself apart before achieving anything approaching complete fusion.
Stranger
Since you discount blast and radiation, I suppose you could instead use the nuclear reaction to generate electricity.
The largest nuclear power plant in the world is the Kashiwazaki-Kariwa plant in Japan. It has eight boiling water reactors with a combined net output of 7965 MW. If you connected that output completely to household LED bulbs you could light 531 million 15-watt bulbs for a combined output of 850 billon (thousand million) lumens and sustain this output for about as long as the plant would run between refuelings.