Hi,

About six months ago I bought two modern F15T8 Philips "Natural Light" tubes for my Dazor desklamp. These are sold as "full spectrum", 92 CRI, 5000K (online stores often sell them under the "Natural Sunshine" name). I really love this tint, reds and browns are vivid despite the cool CCT.

So I bought two F20T12's for my kitchen ceiling fixture. Same brand, same specs, same product name, same light blue package; only the rated life changes: 7500 hours for the F15T8 versus 9000 hours for the F20T12.

However the tints and light quality are different (altough similar for someone who don't pay attention on these things):
- reds and browns look less vivid under the F20T12;
- the F20T12 looks also a bit more yellowish;
- when I move a white pen over a black blackground, I see yellow bands with the F15T8 (which means that there are halophosphates in it, right?) but only black bands with the F20T12 (so I assume there are only triphosphors, right?).

Both fixtures use vintage non-electronic ballasts. I know CRI is a global and partial measure, so that different colour renderings may share the same CRI.

So here's my question: why do the same model of tubes have different tints and phosphor compositions? Is it due to tube diameter constraints, T8 vs. T12? Is it because Philips expects that the F15T8 would be intended to professional desk lamps, hence a better quality than on F20T12 that would be supposed to be for general lighting?

Thanks for your thoughts

The tubes may be the same brand but made by different manufacturers. It could be a batch difference as well phosphor wise. Might even be a difference in the drive level. The best thing to do when getting such high color rendering lamps is to buy a big brand (GE or Sylvania) and buy at the same time from the same source and hope for the best and that they were made in the same factory. Philips uses multiple factories worldwide and the phosphor mix could be slightly different.

this is not unusual.with lots of stuff globally sourced nowadays this is to be expected.many mfrs make mostly comparable items and buy from each other.
i have lots of f15t8 vitalites in service and lots of different oems and appearance/tint/color rendering.
btw the ones with the best color rendering and least spikey spd by my old eyes are the german made ones.
i can see this without a macbeth chart.

OK, thanks guys for your reply, that means that there's nothing weird here (even from well-known brands such as Philips or Vita-Lite, even on full spectrum ranges).
BTW, actually I purchased an additional F15T8 at the same time as the F20T12's (at the same online dealer): both "new" and "6-months old" F15T8's looks identical, so I compared T8 and T12 tubes bought from the same source.

Check the spectrum to see which phosphor the lamp uses. Triphosphors have 5 narrow peaks in the blue, cyan, green, orange and red.
Also: "Full Spectrum" is an american generic term for a fluorescent lamp with a >90 rated CRI and 5000K rated CCT, or for an incandescent/halogen lamp with a neodymium glass, despite their spectrum is far different from natural daylight. In fact, even the natural daylight/solar spectrum, isn't considered a "full spectrum", since it have many absorption lines that the metallic elements on the sun chromosphere absorbs (Fraunhofer lines) .

Unfortunately I don't have the tools to check the spectrum, but I'll ask a friend.

Indeed before trying these tubes for my desklamp I thought "full spectrum" designated "5-band" or so phosphors that mixed more types of phosphors than a standard triphosphor tube and emitted in deep red, but then I understood it was a marketing name as "daylight" simply designates a 6500K CCT whatever the colour rendering. You're confirming my assumptions.   

"Full spectrum" is not different than "LED TV" in meanings. Both are marketing terms that turned into generic names for the products that they were promoted ("Full spectrum" for Ra8>90 5000K fluorescent lamps and "LED TV" or simply "LED", for an active matrix full color Liquid Crystal Displays [LCDs]). 5000K is kinda daylight as well, but less cold than 6500K daylight. While "Daylight" is a real colour name, "Full spectrum", is a generic name and a misleading marketing term.
In fact, CFLs labeled as "full spectrum", have the same Ra8=85 CRI, color and spectrum, as "Non full spectrum" CFLs.

5000K is kinda daylight as well, but less cold than 6500K daylight. While "Daylight" is a real colour name, "Full spectrum", is a generic name and a misleading marketing term.

I understand "Daylight" as any 6500K fluorescent lamp, some having a 60 CRI and some others a 85 CRI. Is it false?

In fact, CFLs labeled as "full spectrum", have the same Ra8=85 CRI, color and spectrum, as "Non full spectrum" CFLs.

That's what I discovered when visiting websites that sell "full spectrum" lamps. I've even seen 80 CRI CFLs labelled "full spectrum" because their high peak in the blue area. They seem to be marketed for both humans and plants.
I don't know whether the lower CRI in CFLs is a real phosphor degradation/temperature issue, or a question of marketing.  

6500 is daylight, 5000 is kinda greener color

i think issue is that CFLs are not aimed at the professional market in the 1st place so they might think "80 CRI is full spectrum enough  to sell it to the home user that will believe anything, and more often than not he compares the CFLs to 40w halophosphor tubes and see that the CFL is better"

My understanding of this is that phrases such as cool white, daylight and full spectrum (and others) are too broad to have major significance. That is why we often see the colour temperature and the CRI for lamps, especially the professional ones. Then it is up to the user to judge if it is "full spectrum" enough for the application

Cool White and Daylight are well defined as 4000-4100K and 6500K respectively

Cool White describes a white colour that its shade is cooler (4000-4500K) than a plain white (3500K) and than a warm white (2700-3000K).
Daylight describes a white colour which have a shade that remainds natural daylight (Bluish white, 6500K).
Both are colour identification names in origin.
By the other hand, "Full Spectrum", is a marketing term in origin, that used to convince consumer that the lamp, have the same spectrum (And therefore color quality) that of the sun from the space (And therefore a perfect color and light quality), and is usually refered to a 5000K color lamp, since this is very close to the sun temperature in Kelvin and also its CCT, as seen from the space.
Therefore, since most US consumers and sellers, identifies a 5000K color temperature as "Full spectrum", and since unlike "cool white" and "daylight", "Full spectrum" is a marketing term in origin (It was also applied to incandescent/halogen lamp with a neodymium glass), it considered a generic term for 5000K color temperature (At least on fluorescent).

This is also what happens with the term "LED TV", which turned the word "LED", as a generic name for televisions and computer screens that uses Liquid Crystal Display (Regardless of backlighting type)(Several stores in Israel, even goes farther, and uses the word "LED" to generically describe a television in general, when they states the word "LED" instead of the word "Television", when they advertising their stock of electronic entertainment products that they offers and sells [Aka simply "LED 55"" instead of "LCD TV 55"" or "55" LCD television").

I dont say that those names are correct - i'd rather name the colors like

2700-3000 - extra warmwhite
3500 - medium warm white
4000 - light warm white
5000 - white
6500 - cool white
8000 - extra cool white

how 3500K can be called "neutral white" is well beyondme

But manufacturers do agree that 2700-3000k is warm white, 4000-4100 is cool white, 6500 is daylight (except in hebrew where it is said as "white" or "cold") and 8000 is sky. Those color names say nothing about CRI - for better description you'd use the color codes like 865 etc

The list above is what I had in mind, except that:

- 2700K is usually labelled "extra warm" for fluorescent but "warm" for leds (however 2700K rated look warmer in fluorescent than in led, probably due to the different spectrum peaks and shape);

- 3000K is usually labelled "warm" for fluorescent and "warm" or "soft white" for leds;

- I personally consider that 4000-4100K looks "neutral" with fluorescent (as labelled) (actually, "yellowish neutral" with halophosphate, "pinkish neutral" with triphosphors) but "medium warm" with leds (I'm not alone since some led flashlight manufacturers label their 4000K models as "warm");

- 10000K HID headlights look violet to me!

I like how led and CFL manufacters explain CCT in their packages, showing a 2700-6500K sliding bar on which the product colour is identified.

About "full spectum" : there are also 6500K fluorescent lamps advertised as "full spectrum", some as plant growing lamps, some as healthy lamps.

I see the 4000K halophosphors, as brownish white, in a 6500K halophosphors atmosphere. If viewed alone, they looks more pinkish white.
2700K and 3000K halophosphors, looks as a very ugly warm brownish or pinkish white
3000K colour called "Soft white" in the US also for fluorescents, not only LEDs.
2700K triphosphors looks like a warm pinkish yellow white or simply a yellowish white at the home, and it is good at homes. But at supermarkets, it looks like an ugly warm brownish pinksih yellowish colour, which is why I don't prefers <3500K lights at commercial locations.
4000K triphosphors, usually looks similar in shade to a yttrium vanadate coated self ballasted mercury lamps (Such as my Philips ML 160W and Osram HWL 160W).