Back yard dusk-to-dawn lights are pretty common. They are also a big source of glare and light pollution.
Here is one of them turned on and I think you'll see what I mean.
Look at the piece of poster board on the right and you should see just how much light it throws sideways and upward instead of down. This is an example of what people who are concerned about light pollution call a "glare bomb".
Look at the picture below and then answer the (trick) question:
Which of these lights is turned on?
The answer is: "both of them"!
It may not look like they are both turned on as many people are used to looking at the source of the light and not the intended target of the light. So let's look at the illumination provided by each lamp:
The light on the right is a retrofitted fixture from Evluma. Notice that it is putting most of its light on where it is supposed to go - down.
They do this with an LED lamp that can be screwed into many existing dusk-to-dawn yard lights. While this LED is a much bluer light than we would like to see, it certainly has much, much better shielding than the light it replaces.
It is a bit pricey (a little over $200), but it also uses substantially less electricity than what it replaces. If you buy one it will pay for itself in a year or two (depending on your electric rates), though lower electric bills.