I have two sets of lights on my Blazer. One set is 11 inches above ground level, the other set is, 67.5 inches above ground level.
If I shine these lights at a wall, on level ground, with a mark on the wall at the height of the lights (11 inches and 67.5 inches), at 10 feet away from the lights, how far down from the level mark on the wall should I point them, so the lights will shine on the ground at 400 feet ?
And, what is the formula for all that ?
I could do it at night, marking on a wall, then aiming them at a target that I would draw, but it is more fun to actually figure out the angles with trig, and aim them with a protractor, and see how close I get.
JOHN:confused:

I don't understand your question really. And I don't have time to read it to try and make sense of it.

Could you draw a diagram?

I'm sure someone with more time will come along and make sense of it, we have a lot of capable mathematicians here :)

I may know what you are getting at. I am not sure, but here goes.

You are 10' away, and want to know how far down to angle your lights so that when you back up 400' away the lights hit the ground. Headlights cast a broad beam, so I will have to assume a line instead of a spread out lightbeam.

You are 10' away. Mark the lower light 0.92 feet above the ground and the higher light 5.625 feet(67.5 inches) above the ground.

Now, if you are 400 feet away. tan^{-1}(\frac{0.92}{400})=0.13178 \;\ degrees

Now, setting at 10 feet away, you would use this angle to mark down the appropriate amount. 10tan(0.13718)=0.023 \;\ feet You would mark down about 1/4 inches in order for the light to hit the ground at 400 feet.

Now, for the 67.5 inch lights. Same technique:

tan^{-1}(\frac{5.625}{400})=0.805668794153

10tan(0.805668794153)=0.140625

You would mark down 0.14 feet. About 1-3/4 inches.

I hope I interpreted you correctly.

Thank you galactus !
That's just perfect!!
John (KI4NDA)