Fortunately a 'daylight saber' doesnt need to "rival the sun" or be "more powerful than the sun" for several reasons:

1. We arent going to be holding up a saber directly in front of the sun itself to look at [which would be foolish and dangerous] so the sun itself does not need to be "rival[led]"...only reflected-sunLIT backgrounds eh?

2. The sun is fortunately 8 light minutes/93 million miles away so its brightness is greatly attenuated by the inverse square law by the time it gets to us...therefore a daylight saber doesnt need to be "more powerful" than the sun to be seen emitting light...if THAT was necessary the only EMISSIVE light sources that could be seen on Earth in daylight would be H-Bombs lol.

3. Jumbotrons, vehicle headlights and commercial signage are all visible in daylight WITHOUT need to "blow out your city's power grid" otherwise the Las Vegas strip, Times Square, or here in Toronto "Honest Eds" [Google it lol] wouldnt be visible except at night.

You are right that daylight sabers represent a technical challenge and we arent 'there' yet but there is no insuperable law-of-physics barrier to them as you seem to be suggesting only R&D time/expense/engineering difficulty...which should be overcome as more efficient light source technology evolves in time.

From what I've been able to gather from daylight lighting specs, a daylight visible saber should require something on the order of 2000 lumens [1650 lumens = 100W incandescent which is visible in daylight - unless held up in front of the sun to "rival" it strawman argument lol]...you are right we can't produce that with a battery powered saber in a standard size hilt NOW, but lets look at it more closely: IF we had a quad die under one dome LED each 'emitter' die would have to produce 500 lumens to be daylight visible...we are halfway there with a U-bin P4 white so its not SO far off though obviously more so for certain colours like blue...WHEN we can double-to-octuple efficiencies depending on colour a daylight saber should be possible with LEDs [but who says LEDs are going to be the most efficient light sources forever anyway?] using similar power requirements as now [or if we had a power breakthrough like room temperature superconductors but THAT would make REAL lightsabers possible so lets fuggedaboud better batteries as the solution]...advanced heatsinking and active cooling will almost certainly be necessary yes but thats just engineering not a physics 'barrier' to daylight sabers.

Engineering is a matter of time and expense [R&D] not possibility or "plausible or just plain busted Mythbusters style".

*paraphrased in best Dionne Warwick singing impression*

Do I know the way to San "NO-WAY-JOSE"...???

Not YET...but that doesnt mean there is NO way to ever get there.

So I wait, patiently.

Meanwhile I'll enjoy the sabers we CAN make now, until they reach my original purpose.

But I'm afraid I'm always going to be what someone called a "brightness *ho**" until then.