# What is the difference between the T4 XM-L and the T5 XM-L?



## frascati (Jan 12, 2014)

I'm not technically adept enough to parse much beyond lumens/mA so I'm wondering why there is a choice available between T4 and T5. 

In short, please explain why anyone would opt for the T4 over the T5 to implement a neutral white xm-l when it appears as if the T5 provides greater lumens per mA. 

Guesses. 
1. The T4 has marginally better power consumption and trades off brightness for battery life?
2. The neutral white xm-l range is 3700 K to 5000 K and the chart above falls short of clarifying that the T4 represents the lower register of this range and the T5 the upper?
3. I give up


Thanks.


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## Yoda4561 (Jan 12, 2014)

Availability is the key word. Some tint bins just don't get many LED's made in the highest possible flux bin due to manufacturing/technology limitations. That results in a situation where *pulls numbers out of thin air* 90% of the leds with the desired tint are T4, 5% are T3, and 5% are T5 or higher. So people end up using what they can get their hands on, which is usually the 90% made in T4. In regards to battery consumption, the higher the flux bin the more efficient the LED, so no you don't gain anything in battery life by going with a T4 over a T6, rather if you run them at the same brightness the T6 will have bettery battery life every time.


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## frascati (Jan 12, 2014)

Thank you for that. Makes a lot more sense. 



Yoda4561 said:


> Availability is the key word. Some tint bins just don't get many LED's made in the highest possible flux bin due to manufacturing/technology limitations. That results in a situation where *pulls numbers out of thin air* 90% of the leds with the desired tint are T4, 5% are T3, and 5% are T5 or higher. So people end up using what they can get their hands on, which is usually the 90% made in T4. In regards to battery consumption, the higher the flux bin the more efficient the LED, so no you don't gain anything in battery life by going with a T4 over a T6, rather if you run them at the same brightness the T6 will have bettery battery life every time.


_
"So people end up using what they can get their hands on, which is usually the 90% made in T4" _

To overstate what might be obvious..., 
does that mean the T5 is likely to be more efficient but not guaranteed to be? 
does it also usually make the T5 more expensive? 
and does it make the T5 more consistent.... that the 12 T5 you order are more likely to share a narrower range of efficiency than the T4? 

If I were to order a dozen neutral white XM-l, and T5 was available, and the relative cost difference insubstantial for such a small order, it would make no sense for me to opt for the T4. Is that right? 

And if you might be thinking at this moment....
_
You're built too low. The fast ones go over your head. Ya got a hole in your glove. I keep pitchin' 'em and you keep missin' 'em! Ya gotta keep your eye on the ball!_

... thanks for your patience


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## TEEJ (Jan 12, 2014)

The higher the bin, generally, the less phosphor and the cooler the tint, and the more lumens you get from a given supply of power.

To get a warmer tint, you get fewer lumens for the same input. IE: Warmer uses more power to make less light.

Why get warmer then?

Some like the way it looks, or, the way things lit by it look, etc. That's it in a nut shell. If making your subject less well illuminated (Less lux on target) is ok as long as the colors look the way you want, then you go warmer. If you'd sacrifice the look for the lux, you go cooler.

Every one has their own preferences, so there's no one "right" answer...and one man's "too yellow" is another man's "perfect tint".


After that, its about cost and availability.


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## DIWdiver (Jan 12, 2014)

When they build these, there's some natural variation from one to the next. So they test them. The chart you posted is from an XM-L2 datasheet, which I can tell because the specs are given at 85C. That means they test them at 85C, and 350 mA. If they put out enough light to make it into the T5 bin, they are labeled T5 (or higher, if appropriate). If not, they are labeled T4 (or lower). The prices for each bin are set to maximize profit. Imagine that at some point 25% of the product falls in T4, 50% in T5, and 25% in T6. Obviously, because of market forces, the T6 will be the most expensive, and the T4 will be least.

Then someone gets a bright idea (pun intended) and makes a tiny change to the manufacturing process. That makes them on average, a little bit brighter. Now they are getting maybe 15, 50, 35%. Once they make enough improvements, they'll stop getting T4 parts at all. By this time they'll be getting into the U bins.

It's tempting to say that T4 will always be cheaper than T5, because nobody in their right mind would pay more money for less light. While they are both in production, it will probably be true. 

But imagine this scenario: I've built a light and sold it to the US Navy. When I designed the light, the best part available was the T4. So that's what's specified in the contract. The Navy wants 10,000 lights a year for 10 years. I can't afford to buy enough LEDs for 100,000 lights right now, so every year I buy for 10,000. Next year the T4 is probably still cheaper. But what about the final year, when Cree hasn't put out a T4 in 5 years? If I can even get T4 parts at all, they are likely to be much more expensive than better, more modern parts.


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## DIWdiver (Jan 12, 2014)

TEEJ said:


> The higher the bin, generally, the less phosphor and the cooler the tint, and the more lumens you get from a given supply of power.
> 
> To get a warmer tint, you get fewer lumens for the same input. IE: Warmer uses more power to make less light.
> 
> ...



+1, except for linking bins with phosphors.

To go up a bin, you don't change the phosphor, you improve the underlying blue led.


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## Yoda4561 (Jan 12, 2014)

frascati said:


> If I were to order a dozen neutral white XM-l, and T5 was available, and the relative cost difference insubstantial for such a small order, it would make no sense for me to opt for the T4. Is that right?
> 
> 
> ... thanks for your patience




As long as the T5's are in the tint range you want, there is no benefit to choosing a lower binned LED. Each flux bin is spaced 7% apart, so a T5 will on average produce 7% more light for the same power than a T4, a T4 will produce 7% more light than a T3 etc. In regards to how closely each LED matches, this is up to production tolerances. It may actually be that the thicker phosphor layers on lower bins result in less standard deviation in % thickness of the phosphor resulting in better matching LEDs. Perhaps the latest phosphor mix used on the U bins is more precisely applied and there's less deviation, no way to know without hand checking each LED as they're not usually sorted that closely at the factory.


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## znomit (Jan 13, 2014)

Yoda4561 said:


> As long as the T5's are in the tint range you want, there is no benefit to choosing a lower binned LED.



If you're building lights to sell and the end user can't tell a T3 from a U2 its beneficial to choose the _cheaper_ T3. And label it U2 like everyone else does.
:devil:


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## Joys_R_us (Jan 23, 2014)

Sorry, I still don't get it (although an engineer). Many high quality flashlights now have the XM-L2 with U2 (cool white) or T6 (normal white) specs. When I look at the Cree table above which I also already came across already, I see T6 in the cool white section instead of 4400 K as it ie supposed to be... !??


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## DIWdiver (Jan 23, 2014)

The bin is not about color. You can get T5 in cool white, or in neutral white. The T5 bin means it will put out between 260 and 279 lumens at 700 mA and 85C, regardless of color. When they get better, you'll start to see T6 in neutral white, and eventually warm white. By then the cool white will be in the U bins.

They start with a blue LED, add certain phosphors to make it cool white and different phosphors (or at least a different mix) to make it neutral or warm white. They can't make the highest bins in warmer colors because the higher percentage of red phosphors used to make warmer colors eat up some of the lumens.


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## Joys_R_us (Jan 23, 2014)

Oh, thx very much. Nice to be here in this forum with lots of knowledgeable and helpful people !


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