One of the long-standing facts about LEDs (Light-Emitting Diodes), is that for any color (wavelength) of light to be emitted, a different semiconductor material was needed, each with a different gap-energy, and therefore also each with a different forward voltage-drop.
What seems to have happened in more recent times, is that in the cheap, mass-production of LEDs, the Industry is realizing cost-reduction, by always producing the famous Blue LED (InGaN), but putting a different phosphor coating onto it, which absorbs most of the blue light, and which emits a mixture of wavelengths to taste.
But this is also the reason for which, when we buy glow-sticks for camping for example, we may no longer find the traditional, deep red glow-sticks as easily as we could before. What has happened is that here too, a Blue LED is used, but a phosphor put onto it that emits red light. And then, a small amount of the blue light passes through the phosphor without being absorbed, so that a ‘pink’ shade of light emerges.
At least, if the ones I just bought are any indication.
One disadvantage to this is the fact that deep-red light tends to blind human vision the least at night, so that assuming night-vision, there used to be advantages to pure red light for signaling purposes. Because the newer LEDs still contain some light-energy at the (shorter) wavelength that looks blue, those LEDs will also have a stronger, undesirable tendency to ‘dazzle’ a person’s night-vision.
My favorite color of glow-stick for camping is actually the green one.
And the reason for that is the fact that several times, I’ve gone camping as part of a group, and on some occasions, certain campers actually tented. When this was being done, we decided on a different color for each camper, and a blinking glow-stick would have signaled to a supervisor, that one camper was in some sort of trouble.
What I was able to do with battery-powered, LED glow-sticks quite easily, was to leave mine on steadily, throughout each night, and still to be able to fall asleep. Like that, the glow-stick was also a source of illumination for my tent. And at each morning, my source of illumination was still working.
And ‘green’ suited me best for that.
If the reader finds a glow-stick in a retail store, in a package that invites “Try Me,” where, the button on the glow-stick works, without the packaging having to be opened, then the reader should expect that this type of glow-stick has been factory-programmed, to shut off automatically after 1-2 hours. This beats any store-clerk having to watch out when the store closes, whether there are still any blinking products on the shelves.
And, this can hinder in certain camping-uses.
These two were hanging on the same item-hook at a Walmart today, and according to their packaging, came from the same company, under the same brand: “Life+Gear”. Each only cost C$ 7.98 +taxes. I know that the 3 additive primary colors are Red, Green and Blue. I’m making the far-out-assumption that, the circuit-diagram of each is essentially the same, meaning that the two colored light-emitters operate at the same voltage, and that the two quasi-white emitters, operate at the same voltage. And yet one looks green, while the other looks pink to the eye. Red ones were not available, even though the stock was plentiful.
When I bought glow-sticks on the Internet in the past, those had thin plastic strips between a battery terminal and the device, which are pulled out before first use, to avoid discharging the battery before sale. In my experience, those will stay on for the duration of a night, or, until turned off by the user.
BTW: ‘Pink’, or ‘Purple’, has ‘Green’ as its complementary color. It would in fact be possible to add a green phosphor to a pink lighting-device, but due to the additive mixing of colors, doing so would just make this light-source slightly less pink.