# What Color Are Phosphors?
Before we can talk about color, we need to talk about the relationship between phosphors and the wavelength of light they produce. Below I have selected a few with particular historical relevance to displace technologies for which I was able to find the peak wavelengths.
| Designation | Color | Peak | Range | Uses | Composition |
| ----------- | ------------- | ------------- | --------- | --------------------------- | ----------------------------- |
| P1 GJ | Green | 525nm | 490-580nm | Monitors | Zn2SiO4:Mn |
| P2 | Green | 543nm | 450-640nm | Oscilloscopes | ZnS:Cu(Ag)(B*) |
| P3 | Amber | 602nm | 504-700nm | Monitors | Zn8BeSi5O19:Mn or ZnBeSiO4:Mn |
| P7 | Blue / Yellow | 440nm / 558nm | 390-650nm | EKGs, Blue with yellow fade | (Zn,Cd)S:Cu |
| P21 | Yellow | 606nm | 554-650nm | | |
| P24 GE | Green | 505nm | 426-640nm | VFDs | ZnO:Zn |
# What Color Were Monochrome Displays?
Real-life colors are affected not just by the wavelength produced by the ideal phosphor but also by impurities, age, glass in front of it, and other factors. Without specifically testing real displays, these are estimated values for the phosphors themselves and not necessarily the perceived colors when new or decades later.
Wavelengths of interest include all of those in the phosphor tables in the [[#References|linked documents]] as well as a few introduced by others online (despite providing no source of reference - these are sourced as `User` below).
| WL | | Color | Source |
| ----- | --- | ----- | --------------------------------- |
| 440nm | | Blue | P7 Phosphor Active |
| 502nm | | Green | User |
| 505nm | | Green | P24 Phosphor |
| 506nm | | Green | User |
| 524nm | | Green | User |
| 525nm | | Green | P1 GJ Phosphor |
| 539nm | | Green | User, incorrectly assigned Amber |
| 558nm | | ? | P7 Phosphor Trail, assigned Amber |
| 600nm | | Amber | User |
| 602nm | | Amber | P3 Phosphor |
| 606nm | | Amber | P21 Phosphor |
# Determining RGB Colors from Phosphor Wavelengths
There are many different techniques people use to convert a wavelength into a hex color. The canonical version used in industry is based on the work of [[Wavelength to RGB Conversion#CIE Table|CIE]] but I have found this powerful resource to be relatively inaccessible. So below I have used a few different approaches that are easier to access.
## Variation 1 - Kuntzleman-Jacobson Technique
Converted using [this online tool](https://academo.org/demos/wavelength-to-colour-relationship/) which is based on the [[Wavelength to RGB Conversion#Kuntzleman-Jacobson Technique|Kuntzleman-Jacobson Technique]]. Most other online tools also seem to generate results similar to this one.
| WL | Hex | Color | Description |
| ----- | --------- | --------- | ---------------- |
| 440nm | `#0000ff` | Blue | Pure Blue |
| 502nm | `#00ff7b` | Green | Spring Green |
| 505nm | `#00ff54` | Green | |
| 506nm | `#00ff46` | Green | Malachite |
| 524nm | `#46ff00` | Green | Harlequin Green |
| 525nm | `#4aff00` | Green | |
| 539nm | `#7eff00` | Green | Chartreuse |
| 558nm | `#bdff00` | ~~Amber~~ | Lime Yellow |
| 600nm | `#ffbe00` | Amber | Amber |
| 602nm | `#ffb700` | Amber | Selective Yellow |
| 606nm | `#ffa900` | Amber | Web Orange |
![[Screenshot from 2023-09-11 18-18-16.png]]
## Variation 2 - User Preference
These colors were selected by a StackOverflow user and they look good, but it isn't clear on what basis the user arrived at these colors so it is not possible to extrapolate the methodology to other wavelengths.
From my own research, it seems clear that the data is almost entirely based on aesthetics and simplicity of representation. There are a number of severe errors and inconsistencies from reality with no explanation.
| WL | Hex | Color | Description |
| ----- | --------- | --------- | --------------------------------------------------------------------------- |
| 502nm | `#00FF66` | Green | Green 3 |
| 506nm | `#00FF33` | Green | Green 2 |
| 524nm | `#33FF00` | Green | Green 1 |
| 525nm | `#33FF33` | Green | "Apple ]\[", "P1 Phosphor" |
| 505nm | `#66FF66` | Green | "Apple //c", "P24 Phosphor" |
| 539nm | `#FFCC00` | ~~Green~~ | "Light Amber" - even though the wavelength is green, the hex color is amber |
| 600nm | `#FFB000` | Amber | Dark Amber "P3 Phosphor" |
## Variation 3 - Spektre Technique
Using the [[Wavelength to RGB Conversion#Spektre Technique|Spektre Technique]] to convert the wavelengths gives more pleasant colors compared to Variation 1, while being far more accurate than Variation 2.
| WL | Hex | Color | Description |
| ----- | --------- | --------- | --------------- |
| 440nm | `#1d23be` | Blue | Persian Blue |
| 502nm | `#00ee69` | Green | Spring Green |
| 505nm | `#00f162` | Green | |
| 506nm | `#00f160` | Green | |
| 524nm | `#00fa39` | Green | Malachite |
| 525nm | `#00fa37` | Green | |
| 539nm | `#00f91e` | Green | |
| 558nm | `#72ee02` | ~~Amber~~ | Yellowish-Green |
| 600nm | `#fa9b00` | Amber | Orange Peel |
| 602nm | `#fa9300` | Amber | Pizazz Orange |
| 606nm | `#f98300` | Amber | Tangerine |
![[Screenshot from 2023-09-11 19-08-42.png]]
## Variation 4 - Bobtato's Modified Spektre
As explained in the [[Wavelength to RGB Conversion#Bobtato's Modified Spektre Technique|section dedicated to Bobtato's technique]] this is using curves fitted over the Spektre shapes, producing similar but not identical colors for a given wavelength.
| WL | Hex | Color | Description |
| ----- | ---------- | --------- | --------------- |
| 440nm | `#1926d3` | Blue | Persian Blue |
| 502nm | `#00f06f` | Green | Spring Green |
| 505nm | `#00f467` | Green | |
| 506nm | `#00f665` | Green | |
| 524nm | `#07ff37` | Green | |
| 525nm | `#08ff35` | Green | |
| 539nm | `#24fd1b` | Green | Harlequin Green |
| 558nm | `#6aef08` | ~~Amber~~ | Bright Green |
| 600nm | `#f68100` | Amber | Gold Drop |
| 602nm | `#f67800` | Amber | Chilean Fire |
| 606nm | `#f66500` | Amber | Blaze Orange |
![[Screenshot from 2023-09-11 19-09-08.png]]
# References
- There is a [big table on Wikipedia](https://en.wikipedia.org/wiki/Phosphor?useskin=vector#Standard_phosphor_types) of standard phosphor types which I used
- I also referenced this interesting [document](http://www.labguysworld.com/crt_phosphor_research.pdf) containing CRT phosphor data by Patrick Jankowiak
- As well as this [flourophore table](https://www.abcam.com/ps/pdf/protocols/fluorophore%20table.pdf) with wavelengths
- I used the [Name that Color](https://chir.ag/projects/name-that-color/) [extension for VS Code](https://marketplace.visualstudio.com/items?itemName=guillaumedoutriaux.name-that-color) to get some ideas for how to categorize the colors
```cardlink
url: https://retrocomputing.stackexchange.com/questions/12835/exactly-what-color-was-the-text-on-monochrome-terminals-with-green-on-black-and
title: "Exactly what color was the text on monochrome terminals with green-on-black and amber-on-black screens?"
description: "I am wondering what were the color shades and brightness of the text appearing on classic monochrome terminals?If I were to recreate approximately the green-text-on-black-screen or amber-text-on-b..."
host: retrocomputing.stackexchange.com
image: https://cdn.sstatic.net/Sites/retrocomputing/Img/
[email protected]?v=6b27f39a6023
```
```cardlink
url: https://superuser.com/questions/361297/what-colour-is-the-dark-green-on-old-fashioned-green-screen-computer-displays/1206781#1206781
title: "What colour is the dark green on 'old fashioned' green screen computer displays/VDUs?"
description: "I'd like to make my text editors display like the old skool white-on-green VDUs of yore that I can just about remember from my childhood. I have this idea they might be easier on my old eyes.I was"
host: superuser.com
image: https://cdn.sstatic.net/Sites/superuser/Img/
[email protected]?v=e869e4459439
```