Revisiting the Light Wash

Eighteen months ago, Andrew and I ran some experiments to see if I could improve the effect of light washing up the backdrop.  I was disappointed with the result, being too subtle to simulate sunrise or sunset.  I was pretty much ready to replace the RGB strips with a simple white strip.

This week, I am travelling for business, and began wondering if I could improve the performance by shining the LED strips onto a reflective backdrop in front of the sky.  If so, what is the optimal angle to shine them at such a backdrop, and how low below the top of the backdrop should the strips be?

Seeing as I was stuck in a hotel room anyway, I figured I might as well trot out the old high school trigonometry and see if I could figure it out.  At the end of the day, there will have to be some experimentation, but perhaps I can shorten the amount.

Backdrop light wash
Backdrop light wash

It was way harder than I expected! Eventually I found that there was a relationship between the angle of the LED strips and the spread of light reflected onto the backdrop.

I found that there is no way to use all the light coming out of the strips and get it onto the backdrop – certain angles go below zero if you try. However, you can capture about a third of it, and make it shine onto the backdrop. Whether the backdrop itself is then sufficiently rough to reflect the light back into my eyes is yet to be determined.


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