On Porch Lights, Optical Geometry and the Ignition Point of Eyebrows

[DaveC426913]

Statement of the problem:
How many bedroom mirrors (of nominal dimensions six feet by one feet) are required to focus my neighbor's porch light with sufficient precision to raise the temperature to the ignition point of my neighbor's eyebrows?

Setup:

• living at this address for exactly one month today,
• neighbor has a porch light of approximately 10 million candlepower
• the porch light is line-of-sight to my bedroom window, distance: 30m
• light is on a motion sensor whose sensitivity is on the "molecules" setting
• duration is "Longer Than Any Sane But Sleepless Person Would Think Possible"
• line-of-sight to my property is bounded by wall of neighbor's house and by my property lines (see diagram)
• we can ignore airspace regulations, 30m height should be well below flight paths
• the 3m easement across the back of my property can likewise be ignored, as it only restricts building of permanent structures, and I expect to take the scaffolding down once my neighbor's eyebrows are well and truly melted off
• assume bedroom mirrors are flexible enough to be bent circular with a radius of 30m. This will give a lit area of 1 foot wide by some arbitrarily small height.
• If more concentration is required, I can split the mirrors vertically to make six inch by six foot mirrors. Anything narrower than six inches is unnecessary, since that it the lower limit of typical eyebrow (full set) width.
• assume light and neighbor's eyebrows are effectively co-incident
• assume neighbor is spherical and in a vacuum (and - if a chicken - at least six feet tall)

The porch light:

The image of my hand on my bedroom wall by porch light:

(in the morning I will find my hand just slightly more tanned than the rest of me)

The configuration:

 

[jrmichler]

I have relevant experience, since I was involved in the "Light Wars" about 30 years ago. Neighbors across the bay installed a very bright floodlight on the top of their cottage. It was aligned so that the edge of the beam lit up their beach, and the main beam lit up my friends beach. They turned it on for the first time when some of my friends were skinny dipping.

Multiple requests to realign it were ignored. So we installed a 1000 watt floodlight aimed at them, and turned it on when their light was on. There was some yelling the first few times this happened, then they got the idea and (I forget) either realigned or removed their light.

A fact bearing on the problem is that the neighbors had a very expensive three story cottage. My friends had a 500 square foot cottage in a group of five cottages that shared 50 feet of beach. The five cottages were built as a resort in the 1920's.

It looks like your bedroom window is nicely aligned to put in a mirror to reflect his light back into his window. Maybe you could pull a slight curvature into your mirror to concentrate the light somewhat.

 

[Tom.G]

A cheaper solution: Black-Out curtains, or offer to buy/make them a (custom?) shade to shadow your bedroom

(although I DO like the 1kW flood light; maybe with a parabolic reflector added
[edit] try searching for Parking Lot Lights, there used to be 1kW incandescents made for them, works only if their bedroom faces you[/edit])

 

[hutchphd]

I shouldn't even go there but does his bedroom face your house? It is not difficult to build a light actuated switch which could control a host of items.....spotlights, lasers, intruder sirens, a vortex gun to rattle only his windows... But perhaps a simple request for an intervening shade on the light could work? That being said LED spotlights run long and cool

 

[jedishrfu]

This sounds like a job for Mythbusters or Archimedes and his polished brass mirrors



https://www.npr.org/templates/story/story.php?storyId=4964987

https://www.wtamu.edu/~cbaird/sq/20...imedes-use-mirrors-to-burn-up-invaders-ships/

https://en.wikipedia.org/wiki/Archimedes'_heat_ray

and now back to our regularly scheduled program.

 

[Drakkith]

I know your pain, Dave. My neighbors moved in last year and installed super bright floodlights over their shed and on the front of their house. They are obnoxiously bright. The only reason I haven't complained to them is because the lights don't shine directly into any of my windows in such a way as to be annoying. But I can absolutely sit on my back deck and read a book by them on a cloudy night.