Hey everyone! I am new to this board and had a few questions about my fluorescent T8's.

I don't know if anyone has heard of the brand Eiko? Back in December I bought a case of T8's from an online distributor which the model number is F32T8/841k. The case comes with 36 bulbs. It has a 4100k color temperature and 85 cri ... you know, the standard. However something is different about these bulbs compared to specifically Sylvania and Philips T8 cool whites. If I were to compare the Eiko bulb with a Sylvania FO32/841/ECO bulb or the Philips F32T8/TL841, the Sylvania and Philips will have a yellowish and slight greenish tint to them. This confuses me because isn't 4100 kelvin supposed to be 4100 kelvin no matter the brand. If I had to guess, if the Sylvania and Philips are truly 4100k, the Eiko's must be like 4500k or even 4600k? It's white without the blueish or yellowish tint to them. That's why I bought them. But if anyone can shed light on the question, it would be greatly appreciated.

Secondly, after having the Eiko's in a 2x4 T8 troffer for about 4 months, I was twisting 3 of the 4 bulbs off to have less light come from the fixture considering it's 4 lamps and in a small 5x5 room. All the bulbs had very little signs of aging until I twisted the 3 bulbs back in. On the last bulb after twisting it back in, the end of the bulb blackened like crazy! After looking fine before I took them out, now it looks like those bulbs that were in use for many years! Now whenever I turn the fixture on, a purplish glow appears at the blackened side for a few seconds then goes away.

Is this bulb now reaching EOL that quick? It still shines bright. Although considering that this fixture is turned on and off 5-7 times a day for the last 4 months, maybe this is normal? All the other bulbs look fine with very little bruise marks, if any!

Sorry for the long topic but I am very eager for these questions to be answered. Thanks to anyone who can shed light on this.

Hey everyone! I am new to this board and had a few questions about my fluorescent T8's.

I don't know if anyone has heard of the brand Eiko? Back in December I bought a case of T8's from an online distributor which the model number is F32T8/841k. The case comes with 36 bulbs. It has a 4100k color temperature and 85 cri ... you know, the standard. However something is different about these bulbs compared to specifically Sylvania and Philips T8 cool whites. If I were to compare the Eiko bulb with a Sylvania FO32/841/ECO bulb or the Philips F32T8/TL841, the Sylvania and Philips will have a yellowish and slight greenish tint to them. This confuses me because isn't 4100 kelvin supposed to be 4100 kelvin no matter the brand. If I had to guess, if the Sylvania and Philips are truly 4100k, the Eiko's must be like 4500k or even 4600k? It's white without the blueish or yellowish tint to them. That's why I bought them. But if anyone can shed light on the question, it would be greatly appreciated.

The same CCT and CRI does not mean the same color. The "CCT" is called "correlated", because it says at which temperature the blackbody radiator spectrum will CORRELATE the best with the discussed spectrum.
The light color is a 2D thing, while the CCT tells only one dimension (to which temperature corresponds the the closest point on the blackbody locus). But it does not tell, how far you are off that curve.
So if the light contains more blue and red, it may get purple without changing the CCT (the extra red compensates the extra blue).

The color rendering does not say anything about the perceived color of the light, but it describes, how accurately are colored objects rendered when illuminated by that light.
So if the shift is not that big, it does influence it at all either.

So you may well have two lamps, one yellowish, one purplish, while both being 4100K and 85 CRI. The purplish has just a bit more red and ble, the yellowish has more of yellow and green.

But what is strange: The eye is most sensitive around the green, so when you "focus" most of the radiated energy around there, you get the highest lumen output without the need to really radiate more power. That is the reason, why most companies tend to shift the color a bit towards the green/yellow from the blackbody "white", it boosts the lumens, so efficacy (lumens vs input power), without really needing to increase the energy efficiency (radiated power vs input power). Doing the opposite is strange, because it means you have to actually generate the light with higher efficiency to get the same efficacy. But on the other hand different wavelengths need different substances and different substances may exhibit different conversion efficiencies, so the combination may be still optimal from what materials are available for them.

Secondly, after having the Eiko's in a 2x4 T8 troffer for about 4 months, I was twisting 3 of the 4 bulbs off to have less light come from the fixture considering it's 4 lamps and in a small 5x5 room. All the bulbs had very little signs of aging until I twisted the 3 bulbs back in. On the last bulb after twisting it back in, the end of the bulb blackened like crazy! After looking fine before I took them out, now it looks like those bulbs that were in use for many years! Now whenever I turn the fixture on, a purplish glow appears at the blackened side for a few seconds then goes away.

Is this bulb now reaching EOL that quick? It still shines bright. Although considering that this fixture is turned on and off 5-7 times a day for the last 4 months, maybe this is normal? All the other bulbs look fine with very little bruise marks, if any!

Sorry for the long topic but I am very eager for these questions to be answered. Thanks to anyone who can shed light on this.

Well, 7 times a day is really frequent switching. If the ballast cold starts the lamps, most of the wear comes from the starts, so it may be, what wore them off.
The thing is, normally the blackening does not start until the emission layer gets consumed. So it may be, the lamps appear perfectly fine most of the time and only short time before EOL they start blacken. And that may have come just when you decided to play with the number of lamps.
And at last: If the fixture uses a common ballast for all 4 lamps, it may be, the output current for each lamp depends on the lamps inserted. You should never operate it in a configuration that the ballast is not rated for (if the ballast label does not explicitely describe how to run less lamps, you should not operate it without all lamps installed). It may happen, when some lamps are removed, the others are heavily underdriven (most important is that in the glow phase), with no cathode heating that may kill the lamps after really a short time.
And beside of that, disconnected lamps do cause quite some stress within the ballast, that may shorten it's life, unless the ballast is really rated for such operation (and there it may happen, than the unused channels actually fail after a while, but because that failure does not influences the used ones, it is not considered as a problem; no one expect the lamp connections would ever change over the ballast/fixture life).

Thanks for the reply! The ballast is an instant start ballast which operates all four lamps. I remember I used to have Sylvania's awhile ago, the fo32/735/eco, and only after a month of switching 5-7 times a day, the ends started bruising and getting darker day by day. Normally what I see is if you leave the lamp off for 2-3 hours or more, a big glob of black and gray goo appears on the ends and normally dissipates after a few seconds. But eventually it leaves light bruises and get's darker and darker as time goes on.
As for the Eiko bulb I have, the end is pretty dark, how much longer do you think this bulb would keep going if the same switching pattern happens.
These bulbs are rated for 24,000 hours at 3 hours a start on instant start ballasts.

There comes a balance point where if you have too many switching cycles, the quality of the lamps matter much less as the electrode wear (the result of which you call end bruising) will overcome any other failure mode, and much quicker than any rated life for said lamp. You could have the best quality lamp with the least manufacture defects and still get a relatively short life from them because of the switching cycle.

You could in theory extend the life of poor quality lamps with a programmed start ballast. Eiko lamps may not be the best (can't talk about experience here, however) but the underlying problem here is the choice of ballast starting method. Many people choose programmed start ballasts for applications with short duty cycles (such as a washroom). Hope this helps.

The darker grayish coat at the ends usually have two causes:
First is the sputtered electrode material. It appears mainly close to the lamp EOL (assume cathode limited) and once it happens, it remains there.

But very similar looking is a kind of dew formed from the condensed mercury. It does form more likely when there are other metal particles, but it does not need them, but on not too much worn lamps it tend to appear just after switch ON, when the rapidly heated electrodes boil off the mercury (when switched OFF, it tends to condense on the metal surfaces). The main distinguishing feature of the mercury dew is it evaporates when the lamp warms up (or at least part of it evaporates, around the hottest parts).
The dew is rather normal and does not relate to any wear or so, it depends on the temperatures and airflow around the lamps, so on the fixture design (some fixtures on some places tend to form it more intensively, others do not at all)


Regarding the switching cycles and wear: With 3hours per start with cold starting method, the main failure mode is already the starting related electrode wear. With pure warm start methods (so programmed start) the border is a bit shorter time, with starts where the ignition is triggered by the filaments just reaching emission or assisted heating cold start (the RS in the US, the 4wire per lamp instant start ballasts as common in cheap CFL or in Europe with cheapeese products) it is just the border.

The cathode design may greatly influence the robustness against sputtering, but it requires more complex wire shaping and that cost extra cents to manufacture. So such quality aspect does influence, how log lasting the tube would be.
Generally with classic designs, the life limitting factor was anyway the cathode life - it gets sputtered even during normal operation (but way slower compare to a cold start), so a quality lamp designed for longer lamp has the cathode assembly longer lasting, so the degree how far the lamp was made as quality vs low cost does influence even the starting cycle life. But it does not have to strictly correlate - some modifications prolong the general life without imrpoving the starting wear, some address mainly the starting wear, yet many still do address both.
It is only in recent years, when other failure modes than cathode fail become visible (atmosphere poisoning, insufficient mercury, glass cracks). The main reason is, the cathodes had improved a lot, so the lamps tend to last so long, those problems appear more frequently. And the thin, high efficient designs put more stresses to the materials as well.

I like Eiko fluorescent stuff. I have an Eiko FC8T9/D and it seems to be a well-made lamp. It has visible mercury condensation despite being marked "TCLP Compliant". I also have a few F8T5/W lamps from them, and while I haven't run them long enough to test longevity, I appreciate that Eiko is still putting out halophosphate White fluorescents. They're the last manufacturer I know of to do so.

I like Eiko fluorescent stuff. I have an Eiko FC8T9/D and it seems to be a well-made lamp. It has visible mercury condensation despite being marked "TCLP Compliant". I also have a few F8T5/W lamps from them, and while I haven't run them long enough to test longevity, I appreciate that Eiko is still putting out halophosphate White fluorescents. They're the last manufacturer I know of to do so.

That's awesome!
I love Halophosphate colors.