Both fluorescent tubes and many mercury vapor lamps have phosphors that make the light more usable. While most semi-modern fluorescent tubes emit wonderful light that is pleasing to the eye with the help of complicated concoctions of phosphors, MV lamps are stuck with much simpler phosphors that produce a much more industrial light that doesn't look nearly as appealing to everyday people.

What is the difference? They both convert mostly the UV radiation of mercury vapor to visible light, right? So why can't MV lamps be high-CRI and beautiful like fluorescent tubes?

Surely there must be a valid reason for this, but I don't know what it could be.

Thanks!
 

It is simple.

Low pressure mercury discharge radiates mostly at mercury resonant line 254nm, which is for sure invisible, while just a very minor amount of energy is radiated at visible lines. So you can construct a phosphor mix on pretty whatever spectral requirements in visible light, be it efficiency, CRI, plant growth, meat counter, festival lights etc etc...

With HPM, things are in reverse. Most of high pressure arc radiated light energy is at visible wavelengths, and a minor part is UV. So using phosphors in HPM lamps is pretty much limited just to augmenting already strong blue-yellow-green light of mercury arc with some phosphor band. Sure, most popular option is to add some red light. Second most popular is to add some extra blue, to avoid that yellow-greenisch coloration.

Spectral balance of HPM lamp can be bent some further by adding a color filter, squeezing a bit of CRI and making CCT a bit lower, see a recent example of super deluxe lamp. But of course at the price of serious efficiency penalty. And while people here rave for super deluxe color, personally I don't regard it that much, preferring pinkish unfiltered deluxe lamps.

It also has to do with the high temperatures in a HPMV lamp. Many phosphors lose their strength at the temperatures used in HPMV lamps.

I use to mistakenly think of why they didn’t use the modern, (at the time), Tri-phosphors in mercury lamps like they did in CFLs? 🤨 until I learned that the mercury discharge tube would make them look awful and dull due to their type of UV 🫣

It is simple.

Low pressure mercury discharge radiates mostly at mercury resonant line 254nm, which is for sure invisible, while just a very minor amount of energy is radiated at visible lines. So you can construct a phosphor mix on pretty whatever spectral requirements in visible light, be it efficiency, CRI, plant growth, meat counter, festival lights etc etc...

With HPM, things are in reverse. Most of high pressure arc radiated light energy is at visible wavelengths, and a minor part is UV. So using phosphors in HPM lamps is pretty much limited just to augmenting already strong blue-yellow-green light of mercury arc with some phosphor band. Sure, most popular option is to add some red light. Second most popular is to add some extra blue, to avoid that yellow-greenisch coloration.

Spectral balance of HPM lamp can be bent some further by adding a color filter, squeezing a bit of CRI and making CCT a bit lower, see a recent example of super deluxe lamp. But of course at the price of serious efficiency penalty. And while people here rave for super deluxe color, personally I don't regard it that much, preferring pinkish unfiltered deluxe lamps.

There is the 365nm UVA mercury line, which is as strong as the visible mercury lines in HPMV lamps. The modern Eu:YPV phosphor use it.

We all know this very well, sure.

But there is a little problem, though.

Vanadate phosphor is not very much sensitive to 365nm. Before going to argue Dor, go ahead shine UVA flashlight on a modern mercury lamp. Old fluorogermanate lights up pretty ruby, but modern lamp shows just a weak pink... Some say sensitivity shifts for a hot phosphor. But... No.

 

@RRK: So why yttrium vanadate mercury lamps glowing brightly under blacklight fluorescent and mercury lamps? Both emits 365nm. Aren't they?

You did this *in person*?

Go ahead, show us!

First, run the lamp in an intended way, on mains power, and capture the spectrum to confirm it really contains rare earth phosphor, and not fluorogremanate, arsenate, silicate, phosphate, sulphide, whatever. Show this sharp 615nm peak!

Second, shine some UVA light and show the lamp phosphor lights up bright orange-red, not a barely noticeable pinkish light.

First, run the lamp in an intended way, on mains power, and capture the spectrum to confirm it really contains rare earth phosphor, and not fluorogremanate, arsenate, silicate, phosphate, sulphide, whatever. Show this sharp 615nm peak!

Nowere is said what kind of MV lamp it is in the picture you linked nor which type of phosphor it has...

You did this *in person*?

Go ahead, show us!

First, run the lamp in an intended way, on mains power, and capture the spectrum to confirm it really contains rare earth phosphor, and not fluorogremanate, arsenate, silicate, phosphate, sulphide, whatever. Show this sharp 615nm peak!

Second, shine some UVA light and show the lamp phosphor lights up bright orange-red, not a barely noticeable pinkish light.

Also: I remember that I had a Flash Light blacklight CFL which caused all of my SBMV lamps to glow red color.
But my 365nm LED flashlight indeed barely causing the phosphor of my SBMV lamps to glow red color.
Sorry that I didn't captured this.