I wrote about using a ping ball as an LED diffuser in this previous article. One major issue with this idea was that the LED has a focused light that creates a bright spot on the ball opposite where the LED is. You can see problem in the picture here.
There were a lot of great comments with suggestions for improving the LED diffusing. I put several to the test in this article to see which works best. The ultimate goal is a brightly lit ping ball with out the bright spot. I did find a few good answers and a few bad ideas as well.
I also play with labeling the ball so that it shows some text on the surface when lit. The general idea is that when a ball indicates some kind of fault, it would show some details of the fault, projected on the balls surface by the LED. I had some limited success with this idea.
I used the adjustable current source mentioned in this previous article and the bread board power supply module mentioned in this article to power the LED. I went though my collection of LEDs and found a few bright RED LEDs which I purchased some time back from Alan’s Electronic Projects. I wanted some very bright LEDs with large clear bodies to experiment with.
The adjustable current sink made it very easy to set whatever current I wanted in the LED. I played around and learned a few things. LEDs will take a great deal more then their maximum rating. Most LEDs max out at 30mA. High brightness LEDs generate a good amount of light at about 5mA. If you push the current up, the LED gets brighter to a point. At some current, about twice the max rating, the LED will get dimmer. I think it’s heating up at this point. The LEDs do get hot, mostly along the leads. The plastic body does not conduct heat well so it travels out the LED legs. If you are pushing an LED beyond it’s normal limits, check its temperature at the leads.
I was able to pump 300mA into an LED. It did get hot and dimmer after about 60mA but did not fail. I ultimately did blow out an LED when I knocked my current set point diode limit out of the breadboard. I was using it’s ground lead as a meter connection point and bumped it. For a brief second the current sink tried to pull more then an amp. I did not even see the LED brighten up. It just went out as if power was disconnected, no flash of light, smoke, or popping.
I set the LED current to 40mA after playing around with the current a bit. At 40mA the LED was bright and its leads did not get hot.
As you can see in the picture here, I did figure out how to diffuse the LED to make an even lighting of the Ping Pong ball. I found that you can file or sand the top of the LED or just cut the top off completely. The later is very easy with a hack saw blade and your power drill.
In this picture you see a cordless drill with an LED in the chuck. This trick made it very easy to cut the tip of the LED off. I used a small copping saw, laying the blade against the front edge of the chuck. Moving the saw back and fort with a light pressure was enough to cut the top off as you can see in the picture below. This works very well to diffuse the LED. I also found that filing the top with a small rat tail file works. The filing was harder to do and did not work as well so if you have the option, I recommend cutting off the LED top.
Other ideas tried
On of the commenter’s suggested that the top of the LED could be covered with sharpie ink. I did try this as you can see in this picture. Instead of a bright spot it was a darker spot and the overall light level was substantial reduced. I tried using Red ink as a test too. Just in case it would let some of the light through, to keep the brightness up. I believe that the brightness of the ball is greatly effected if you end up blocking or absorbing the LED light. Filing or cutting the LED top is better.
A commenter suggested that Styrofoam balls would work better then Ping Pong balls. I thought that would be a neat thing to try. I don’t have any foam balls to try but I did find some packing foam and pushed an LED into that. It does light up the foam and even has a neat effect, sort of like lava. But again it dimmed the light greatly. I do believe it did a good job of diffusing the LED and the effect is very neat. If you were building a model volcano, this would be the way to simulate lava.
Light up text
One of the ideas presented in the previous article was some way to label the Ping Pong ball LED light so that it would show the fault type or some other helpful indication. This text or icon would not be apparent when the indicator was off, but would show well when the LED was on. Of course you could write on the outside of the ball, this would work fine except that it would be present when the LED was off. Ultimately, I think this is the best answer but there were some suggestions for neat tricks that I wanted to try.
First I tried to make a small sign with paper, the idea was that the bright LED could shine through the paper and project the text on the inside of the ball to be seen outside. The long tail of paper was used to position the sign inside the ball though the same hole the LED goes in. The paper did not work at all when wrapped around the LED. I cut open a ball so that I could force the paper against the inside surface of the ball. This worked but not real well either.
The next thing I tried was marking on clear plastic with the sharpie and inserting this though a slot in the ball. This did work although it did not provide a strong effect. The text was invisible with the LED was off, showing only when the LED was on. As you would expect, the closer to the balls surface the film was, the less distorted and darker the image was.
I tried cutting a ball in half, writing the label on the inside and sticking it on top of the LED ball like a hat. This worked as you can see but I like the clear film better. Lastly, I tried putting the ball I cut in half back together. I
just taped it crudely but this might work with some glue or clear tape and careful work.
If you want a label that only shows when the LED light up, then the clear plastic film inserted though a slit is probably the best thing I tried. I could see this film being printed to have icons and possibly color pictures even using a white LED. Maybe even slide film stuck inside the ball or near the LED to project the picture onto the Ping Pong ball from inside.
The weather indicator could be a few Ping Pong balls, each with an actual slide picture of the weather conditions. A cloudy sky for example. When the weather conditions are cloudy, the ball for cloudy sky lights up showing a cloudy sky picture. I wonder if you could use multiple white LEDs each with a separate picture attached to the top of the LED. That way a single orb could show multiple conditions with icon projections. With a white LED and color film you should be able to do a color projection.
I don’t have any slides to test this with. The multiple LED test would probably require the resolution of slide film. I could print some color images on clear film to try but the resolution would probably require that I keep the film against the inside surface of the ball.
Any other ideas to try?