# average lamp life expectancy?



## cognitivefun (Mar 22, 2005)

What do you think a P90 or P91 lamp life is like? Or the lamp in a TL-3?

Any experience with lamp lifetimes? Any input is appreciated. Thank you.


----------



## AW (Mar 22, 2005)

I read somewhere about the xenon bulbs having a 25 hours lifespan.


----------



## socom1970 (Mar 22, 2005)

SF cust svc. told me approx. 30 hours, but I've heard of SF LA's lasting over 100 hours. /ubbthreads/images/graemlins/confused.gif


----------



## LightObsession (Mar 22, 2005)

How about the lamp in a Brinkman Maxfire?


----------



## rajanf1 (Jul 12, 2005)

I can't find the life of streamlight's tl-2 lamp in their literature. Can anybody point me to the right information? Also, does the tl-2/3 lamp blow if you drop the flashlight (any experience on this)? tia.

(was going to start a new thread but found this instead)


----------



## PoppyGoddess (Aug 3, 2005)

I happened to have just done some research on this subject. The average life actually has a very wide variability. This life is measured by running the bulb continuously. But 100 hours off a 20 hours spec bulb seems too much. PentagonLight says 25 hours on the B-X2 bulb. But I was told it can vary between 15 to 35 hours easily. I also called Surefire. They gave 30 hours.


----------



## js (Aug 3, 2005)

The average life expectancy of incandescent lamps is measured in two different ways. Some lamps have a fill gas, such as xenon or krypton or argon, but do NOT have a halogen added, such as idodine or bromine. These lamps blacken over time, and have a continually decreasing output. (The stock mini-mag bulbs are a good example of this). IIRC, their life rating is the number of hours, on average, that it takes for the lamp to decline to 85 percent brightness.

Other incan lamps have traces of a halogen added, and are called "halogen lamps". It should be noted that almost all "xenon lamps" are in fact halogens, because I know of no company that would go to the expense of using a mainly xenon fill gas mixutre, without adding a trace of a halogen. It would make no sense. So in general, xenon and halgoen are not competing types of incandescent lamps, although it is theoretically possible to make a xenon lamp without adding a halogen.

Anyway, the halogen in the fill gas actually transports tungsten atoms which have been deposited on the glass wall of the lamp to the filament, where the intense heat causes the tungsten atom to be released from the iodine atom and be re-deposited on the filament. The Brinkmann Nexstar 2AA T1 xenon 2.4 V lamps do in fact have a halogen in the fill gas, because they do NOT blacken over time. Here at work we have been using the same Nexstar lamps in our mini-mags for 6 months straight, an average of 8 hours a week, and they are no dimmer than they were at the beginning.

So, halogen lamps life rating is the AVERAGE number of hours of life until the filament burns out. Welch Allyn does this using a controlled, constant, DC voltage source, which would be the ideal scenario. Anyway, this is a statistical thing. If you took 100 halogen lamps and ran them all continuously at the same voltage, at some point 50 would have burned out and 50 would still be running. THAT is the life rating in hours. But it should be obvious that many (half) will have burned out sooner, and half later. The spread, or standard deviation, depends on a number of factors which I am unaware of, but I can tell you that it is significant. It is more than 10 percent, I would guess.

This means that while unlikely, it is quite possible that someone got 100 hours from a P60. Entirely possible. It's also possible that some poor bastid only got 5 hours.

In any case, *there is no standard life rating for all halogens or any other type of incandescent lamp*. For a given lamp, the hours of life depends directly (but not linearly) on the applied voltage. Increase the voltage by only 10 percent and you reduce the life by more than a factor of 3. Thus a 6.0 volt lamp rated for 30 hours of life driven at 6.6 volts will only have a 10 hour life. (on average). The formula for halogen lamp life re-rating is as follows:

Lr = (Vd/Va)^12*Ld, where Lr is re-rated life, and Ld is design life, and Vd is design voltage and Va is applied voltage.

As you can see the re-rated life goes as the *twelfth power* of the ratio of design to applied voltages. That's HIGHLY non-linear.

One consequence of this is that when direct driven from batteries lamps take the biggest hit on their filament lives at the beginning of the battery capacity, when the voltage is highest. So those who are always changing thier batteries (or recharging) early will be running thier lamps harder than those who try to get the last drop of juice from thier batteries.

Also, a cold filament has a very large inrush current at start-up, which is hard on it and reduces the life. This is why regulated incandescents, such as the SF A2, or my M6-R, have a soft-start feature which limits the current for the first 50 to 100 mili-seconds or so. This is claimed to prolong filament life, and it certainly doesn't hurt, but by far the most important factor in getting the most life from a filament is precise voltage control, or at least prevention of volage spikes. Just a few seconds near the melting point of the filament takes many minutes off of the life of the lamp.

What I'm getting at, is that filament life also depends on HOW you use your flashlight. It's just an average, best-guess kind of number.

And, yes, the P60 and P61 and P90 and P91 lamps are all officially rated by SureFire at 30 hours. Going by the CCT (i.e. beam-color or "whiteness") and by known over-drive limits, I would guess that this is a touch on the conservative side. It's probably actually more like 35 or 40 hours.

For those of you who really want more punishment, I present the "rule of threes" from halogen lamp design:

At a CCT of 3330 K a lamp has an efficiency of 30 lumens/watt, (which corresponds roughly to 30-35 hour life depending on the fill gas and other factors). Every 3 lumens/watt increase or decrease in efficiency raises or lowers the CCT by 100 K. 37 lumens/watt is the practical upper limit of efficiency and overdrive, which would correspond to a CCT of 3550 K. Unless you are a modder I doubt very much that you will have seen an incandescent lamp pushed to this level of over-drive. It is an almost religious experience (or it was for me). Most professional photographic type lamps, which require high CCT, run at 3200 to 3400 K, and this is quite white (for an incan). The SureFire P60 and P61 are not as white as this, but are close (with fresh batteries), so I'd say, going by beam color, that this corresponds to a 40 hour life. But it's just a guess, and there are factors which affect this, most especially whether or not xenon was used as the fill gas. Xenon can increase luminous efficiency by about 5-10 percent, which corresponds to a CCT increase of 100 K. This can only be used in "low" voltage (less than 50 volts) lamps, otherwise you'd turn your incan into a poor excuse for an HID. hehe.

OK. Sorry if it seemed like I was playing professor. Just thought that maybe some people might be interested, being flashaholics and all.


----------



## pradeep1 (Aug 3, 2005)

Jim you have collectively raised our intelligence and awareness and at the same time collectively made us all feel dumb! Thank you. /ubbthreads/images/graemlins/tongue.gif


----------



## js (Aug 3, 2005)

Ahhh, errrr, aaahh, sorry about that last bit! I honestly didn't mean to make anyone feel dumb. I was just emphatic about certain things (like the variability of filament life with drive voltage) because they are so important that they cannot be stressed enough. Hotwire 101, as it were.

But anyway, sorry that I came across this way.


----------



## bwaites (Aug 3, 2005)

Jim,

As always, no matter how many times we discuss something, I greatly appreciate it when it is written down. 

I have copied your post, with appropriate attribution, and will include it with mods I send out so people will understand the color/life issues inherent in highly stressed lamps!

Thanks again!

Bill


----------



## Phaserburn (Aug 3, 2005)

Jim, seriously nice summary, dude. Should be part of a permanent sticky or something, so it doesn't get lost over time.


----------



## 270winchester (Aug 3, 2005)

[ QUOTE ]
*js said:*... Unless you are a modder I doubt very much that you will have seen an incandescent lamp pushed to this level of over-drive. It is an almost religious experience (or it was for me). 

[/ QUOTE ]

LOL /ubbthreads/images/graemlins/buttrock.gif 

That's so true!!!

I thought I saw my creator(well, whatever the secular coutnerpart of god is) when I lit up my Osram 62138HLX with 12 cells...

And Js, just on the side, what type of gas is in the newer Tigerlights? I remember the sales rep told me that it was a Halogen lamp, but my lamp is blackened considerably after a month of regular use(about 20 minutes a night)...


----------



## SilverFox (Aug 4, 2005)

Hello Jim,

I have data that suggests some lamps have a life expectancy of 8 hot turn on's... /ubbthreads/images/graemlins/grin.gif 

Like Bill, it is wonderful to have these thoughts presented in written form. 

Thanks.

Tom


----------



## js (Aug 5, 2005)

[ QUOTE ]
*270winchester said:*
. . .

And Js, just on the side, what type of gas is in the newer Tigerlights? I remember the sales rep told me that it was a Halogen lamp, but my lamp is blackened considerably after a month of regular use(about 20 minutes a night)... 

[/ QUOTE ]

270,

It's a halogen lamp, so if it's blackening on you, it is defective. E-mail Michael Teig at [email protected] and tell him about it, and I'm sure he'll warrantee it.


----------



## TORCH_BOY (Aug 5, 2005)

Up to 25 hours sometimes more, depends on battery types used, how frequently the light is switched on/off, temperature, bumps, knocks ect


----------



## Dave. (Mar 28, 2007)

I was just pondering the blackening and now poor output of my P91 and was going to post something about it when a search for "blackened P91" threw up this thread. I was so impressed I am bringing it to the top again! 



js said:


> Just thought that maybe some people might be interested, being flashaholics and all.



You got that right! Seriously good post Jim, and thank you for all the information. 

As for me, this is in fact my very first P91 coming to the end of it's life, and the reason I was pondering it's blackened state is because I was wondering just how long the poor thing intends to drag out it's ever decreacingly bright life!

It's already down to about the same output as a fresh P90 I have, or indeed my L4, and has been going that way for some time now. It's just a little over 7 months old at this point, and has been used pretty much daily since I got it for anywhere from 5 to maybe 15 minutes a day. Averaging at 10 minutes a day that's a total of 35 hours, plus whatever time I've put on just playing about with it. Not bad really, and spot on Jim!

At this point I would already have ditched it, sad as that may be before it actually burns out, but I am waiting on some new cells to use with a new body so the next P91 is reserved for that. Plus I am kinda attached to the guy now... 

So Jim you already answered my question and more, and I guess this P91 will continue limping on down through the ratings until it's good and ready to quit. The thing is the change is so gradual it took me a while to realize it wasn't that the batteries were always running flat and that something more was up! Now I know to keep an eye and retire assemblies before old age really takes its toll and not hold out for the "pop". :thumbsup:


----------



## mdocod (Mar 28, 2007)

js pretty well covered it....

but to elaborate further I think it is worth mentioning that there is going to be a difference in life depending on which batteries are chosen to drive the lamp....

9V lamps are a favorite of Li-Ion users, on 3 fresh primaries, a lamp like the P90 sees voltage around 9V for a few seconds, the first few times it's turned on (if they are short increments)... so primary cells really work the lamp hard at the beginning, but then they settle down and run a P90 at more like 7.5V for most of the run. The advantage of running Li-Ion is that the bulb never has to deal with the initial voltage spike of ~9V, ~8.2V on large (18650) size cells is the highest voltage the P90 would have to tolerate. 

When driving high power lamps like the P91, high power Li-Ion cells actually push the lamp significantly harder than primaries would have throughout the duration of the run. The result is that lamp life is overall going to be slightly less, especially for those who "top up" their Li-Ions regularly.


----------



## LiteTheWay (Mar 28, 2007)

A great post JS - very illuminating - really!


----------

