Another use for thee bane of civilized world, junk mail.

[Toolmaker51]

Really! Beyond fire tinder, wrapping odd items, cutting patterns?
My driveway has a mercury-halogen flood light attached to freestanding garage. While they might work best high above area to be illuminated, whoever installed mine, [pre 2005 on property built 1902...] got a leetle-beet carried away. We call that a lottle; like a little, but a lot, lol.
Bulb has burned out after a few years constantly on, seems a timer or light sensitive switch is in order, but I digress. Trying to gauge height by tape measure's a joke, best tapes only stand out 11'. From second story [9'5" ceilings plus grade] window ledge, still had to crane my neck to see the lamp fixture. Yikes this isn't a driveway light, it needs an aircraft warning light of its own; a lighthouse 1200 miles from nearest coastline, maybe signal to extra-terrestrials? ET didn't need a phone, a convenient beacon is in my side yard!
I know of, or personally, almost everyone who's lived in this house since being built, one must be a clone hiding his purpose here....

Anyway, my efforts after dark were a failure too, wall texture and angle wouldn't disclose mark from my laser level.
Next day, disposing junk mail I hit upon this solution. By folding over top edge of paper to adjacent side, an accurate square results. Folding two opposing corners creates an accurate 45°. Next, tape plastic drinking straw to the 45° edge.
as usual, click the pic for a less microscopic illustration.
Step forward or back, until intended object appears through the straw, while holding corresponding paper edge parallel [or perpendicular if you prefer] to the ground.
Mark the spot on the ground at your toes. Step back additionally the height of your eye from ground level. That new point is intersection of 45° from whatever object viewed to figuratively horizontal plane. Measure distance from that second mark to a spot as close to directly under [plumb] the object sighted in the straw.
My light turns out to be about 31 feet up, in 1" rigid conduit!
That bit of geometry will help ordering a scaffold and suction cup tipped bulb wand. I have 15' feet of scaffold, 4 jackscrews, and a 12' wand, have to trust ability to reach up and maneuver a $25.00 bulb.....hmmmm
Or be an OSHA poster boy with step ladder on the uppermost scaffold planks?