I would like to understand the optics in this LED pin-spot light, Please.

[colinbm]

I would like to understand the optics in this LED pin-spot light, Please.

The LED is mounted on a star base & has a collimating lens in front of the LED then there is a convex lens at the front of the snoot.

With shining the light up close say, 300mm / 1ft, away from an object the light is a nice round 50mm / 2" circle, but when shone across the room it is an image of the projected LED.

Yes I am surprised they have not earthed the heat sink as it is mains supply ?

[dabateman]

I counted 3 lenses. One directly mounted on the LED. It was quite large, you saw it when he swapped out the original LED.

Then a planar convex lens used in front, possibly 20-25mm in diameter that might be between 50mm to 100mm in focal length. The flat side facing the LED. This one he was adjusting with the spacing from the LED. His new configuration needed it much farther than the original.

The last optic is a bi convex lens possibly 100mm focal length at about 38 to 50mm in diameter. Hard to see exactly the size but looked less than 2 inches (50mm). The curvature was clearly more than a 150mm focal length lens. But not a bulbous as the 75mm I have. I justgot a fused silica 50mm round 39mm focal length lens. Very fun.

So I am guessing the optics based on the recent fused silica lenses I have and have been playing with.

There might be a software program around to type this in to get the best focal lengths for projecting.

Based on the cost of his unit. I would also guess them to be standard BK7 glass elements. So wavelength cut off around 350nm.

Which is not bad at all for an LED, since there are very few at 340nm and less.

You could buy one of these and flip out the chip for yours and see if it still works. With the correct driver of course, which I still haven't gotten my head around yet.

 

[colinbm]

Thanks Dave, Yes I have one, blue 460nm, was sold as a 30w, but only draws 2.5A at 240V.

The planar convex lens in front of the LED is plastic, the bi-convex lens is glass if unknown formula.

LED drivers are a whole science of their own.....

[Stefano]

I guessed the video before opening your link. I saw it too. You see a circle if you are not far enough because you see the unfocused image of the LED.

[colinbm]

Why would you want the projected image of the LED ?

[Stefano]

Why would you want the projected image of the LED ?

Because that's the narrowest beam you can get. You can not collimate an LED or a light source as much as you want (except for lasers, which are still diffraction-limited, but that's another thing). If you have an LED and a convex lens (the best is to use a plano-convex lens with the flat surface towards the LED), and you put the lens above the LED, you will notice that the beam becomes narrower and narrower as you increase the distance between the lens and the LED. At a certain distance, correlated with the focal length of your lens, you will see a projected image of the LED on a wall or something (far away from you). If you keep moving your lens, the image will become bigger and bigger again. It is like using a magnifying glass under the Sun to burn things (even if that isn't collimation, but "re-concentration"). You can't make an infinitely small spot. When you have the minimum spot size, what you actually have is a miniature image of the Sun's disk.

[colinbm]

Thanks Stefano, I can see it clearly now.