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Comment by ninjinxo | Hacker News Reader

Tennis balls are fluorescent; UV light gets reflected back as a set wavelength. This means they'll be brighter than a non-fluorescent yellow/green and thus easier to see. The amount of UV light (time of day, natural vs artificial light, overall light levels) will push the subjective colour between green and yellow.

This becomes a minor consideration when doing tennis court lighting upgrades, as Metal Halide lamps emit UV whilst new LED ones don't. Since tracking of the ball is primarily based on strong and consistent contrast against the background, having a UV light component that only lights the tennis ball is a major boon.

Tennis can be played under blacklight with relatively weak lights: https://www.youtube.com/watch?v=-x4mfQITXtM

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I wonder how many daily things still have fluorescent elements. In the 90s there was a little fad (my ikea bed light has a fluorescent switch, and we had a few items like this).

LED replacements for Fluorescent tube lights are very common now. took me by surprise because for some reason the idea did not register until I saw them when I needed a replacement.

end of summer they finally replaced the remaining halogen street lamps in my neighborhood, we had an every other arrangement. now I have light the equivalent of a full moon which is both good and bad out front

There are 3 different kinds of LED T8 replacement lamps. ‘Type A’ use the existing fluorescent ballast, ‘Type B’ use an external LED driver, and ‘Type C’ use a driver integral to the lamp.

White shirts and office paper have fluorescent dyes.

This is also how "whiter than white" detergent works.

And why bees will sometimes harass people that look too much like a tasty flower.

> Tennis can be played under blacklight with relatively weak lights: https://www.youtube.com/watch?v=-x4mfQITXtM

1:14 "The balls we use are green dot balls and orange balls"

So they are not using standard yellow balls for UV light games.

They're using low compression (lower speed, kid friendly) balls, often they're the same colour as your standard adult tennis balls just with a small alternatively coloured circle to indicate.

https://www.tennis.com.au/learn/rules-and-scoring/10-and-und...

Look at the box of balls at 1:30.

> 1:14 "The balls we use are green dot balls and orange balls"

> So they are not using standard yellow balls for UV light games.

A "green dot ball" is exactly the same color as a standard ball, except it has a dark green dot stamped on it.

Being fluoreszent makes a lot of sense, as it vastly increases the brightness of the balls. Hadn't thought about them being fluoreszent. But for the fluoreszent effect, it is sufficient that the light has a shorter wavelength than the floreszent color. So any wavelength from normal green into the blue spectrum should work, no need for UV for that.

> for the fluoreszent effect, it is sufficient that the light has a shorter wavelength than the floreszent color. So any wavelength from normal green into the blue spectrum should work, no need for UV for that

That is not how fluorescence works. You have a fluorescence excitation spectrum offset from the emission spectrum and there is a peak. I don’t have the spectrum for a tennis ball, but it very well could require UV light for any meaningful fluorescence

https://www.sciencedirect.com/topics/chemistry/fluorescence-...

Yes, of course, there is some offset between the absorption range and the emission wavelengths. But there is no requirement for the absorption to be in the UV region. The absorption range is also wide peak. All the fluoreszent colors which "work" with e.g. car headlights have a sufficiently strong effect in the visual range. It is also an easy test for fluorescence to shine e.g. a blue light at something which has a strong orange color. If it still is strong orange, fluorescence obviously is the dominating effect. I don't doubt that UV light shows a strong fluorescent effect, especially as you cannot see the UV light itself, but of course the fluorescent emission it is causing.

Is there much use of fluorescent colors that work in car headlights? For signs and markings, reflective paints seem to be more effective in showing up under headlights, particularly as the light is directed back towards the source, rather than scattered widely.

The article below describes the benefit of fluorescent dyes under weak natural light, as they can use the UV component of natural light to increase the amount of visible light reflected. Downshifting visible light to a longer wavelength, which is what fluorescence excited by visible light would do, would reduce the intensity of the reflected light.

https://www.3m.com/3M/en_US/road-safety-us/resources/road-tr...

This discussion could use some examples, and there seem to be some named dyes here that are excited by visible light. On the other hand, the simple fact that it was an issue in the replacement of tennis-court artificial lighting shows that UV excitation is a factor in the fluorescence of the dye used for tennis balls.

https://www.thermofisher.com/us/en/home/life-science/cell-an...

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