FROM: snoll@advancedphotonix.com (Steve) SUBJECT: Incandescent Lamp Life - overvoltage effects? DATE: 5 Dec 2001 08:45:31 -0800 ORGANIZATION: http://groups.google.com/ NEWSGROUPS: sci.optics I'm using a grain-of-wheat type lamp that I would like to run over its rated voltage and at an elevated ambient and would like to know if there are formulas to predict lamp life. The lamp is a 7152, a tiny 0.125" x 0.14" bulb rated at 5V 0.11A and 40000 hours. It will be operating in an ambient of +70C. Does that temperature have a significant effect on life? And... is there a way to predict, for example, what over-voltage can be applied and still obtain 1000 hours life? I know there are rules of thumb for "regular" light bulbs, but I don't know if they are scalable to such miniscule lamps. FROM: skeckhardt@mmm.com.deletethis (Steve Eckhardt) SUBJECT: Re: Incandescent Lamp Life - overvoltage effects? DATE: 5 Dec 2001 20:10:00 GMT ORGANIZATION: 3M Visual Systems Division NEWSGROUPS: sci.optics In article , snoll@advancedphotonix.com says... > >I'm using a grain-of-wheat type lamp that I would like to run over its >rated voltage and at an elevated ambient and would like to know if >there are formulas to predict lamp life. > >The lamp is a 7152, a tiny 0.125" x 0.14" bulb rated at 5V 0.11A and >40000 hours. It will be operating in an ambient of +70C. Does that >temperature have a significant effect on life? And... is there a way >to predict, for example, what over-voltage can be applied and still >obtain 1000 hours life? > >I know there are rules of thumb for "regular" light bulbs, but I don't >know if they are scalable to such miniscule lamps. The rule of thumb for larger lamps is that life goes as the negative 13th power of the ratio of the overvoltage to the standard voltage. I would expect it to apply to miniature lamps because overvoltage increases the temperature of the filament and sublimes the tungsten regardless of size. Given that the filament is at 3000 K to begin with, I would not expect 70 C to matter. -- Best regards, Steve Eckhardt (skeckhardt@mmm.com) FROM: w.j.markerink@a1.nl (Willem-Jan Markerink) SUBJECT: Re: Incandescent Lamp Life - overvoltage effects? DATE: Sat, 08 Dec 01 21:49:47 GMT NEWSGROUPS: sci.optics In article <9uluuo$lr8$3@magnum.mmm.com>, skeckhardt@mmm.com.deletethis (Steve Eckhardt) wrote: >In article , >snoll@advancedphotonix.com says... >> >>I'm using a grain-of-wheat type lamp that I would like to run over its >>rated voltage and at an elevated ambient and would like to know if >>there are formulas to predict lamp life. >> >>The lamp is a 7152, a tiny 0.125" x 0.14" bulb rated at 5V 0.11A and >>40000 hours. It will be operating in an ambient of +70C. Does that >>temperature have a significant effect on life? And... is there a way >>to predict, for example, what over-voltage can be applied and still >>obtain 1000 hours life? >> >>I know there are rules of thumb for "regular" light bulbs, but I don't >>know if they are scalable to such miniscule lamps. > >The rule of thumb for larger lamps is that life goes as the negative 13th power >of the ratio of the overvoltage to the standard voltage. I would expect it to >apply to miniature lamps because overvoltage increases the temperature of the >filament and sublimes the tungsten regardless of size. Given that the filament >is at 3000 K to begin with, I would not expect 70 C to matter. Btw, does the distinction tungsten vs halogen matter in this context? And/or: does the formula apply also in reverse, lower voltage, for both types? All the way down to 0 volt? In specific: while browsing for automotive-base type LED-bulbs, I came across the distinction 24 volt vs 28 volt....I know the latter is a typical aviation specification, but I never thought about incandescent bulb life differences....all this in the context of having a 24 volt Land Cruiser (and already facing odd idiosyncrasies, like a minimum wattage for H4 bulbs of 70/75W, while 12v bulbs are 50/55W minimum (due to filament shape/strength/resistance issues I believe)....also the reason why Canadian 24v Cruisers have 12 bulbs, one tapping off each battery (nasty stuff in the context of ground vs hot wire....both wires are hot on the high end battery....but I digress....;)) Or: apart from the fact that I would need a (28/24)^2 = 1.36x stronger wattage to get the same light output, would my bulb life increase by a factor (28/24)^2 = 7.42x? All this assuming that a '24v' bulb is indeed designed for 24v, and not the typical 28.8v that a 24v alternator delivers, just like a 12v alternator delivers 14.4v; and that '28v' is indeed a different spec in this context. Would love to hear some educated opinions on this matter....:)) (all this in the very practical context that I am mounting some sidebars on the vehicle, which make accessing some side-markers and side-indicators very hard to access....the more life I can stuff into them before bolting the hardware on, the better....:)) -- Bye, Willem-Jan Markerink The desire to understand is sometimes far less intelligent than the inability to understand [note: 'a-one' & 'en-el'!] FROM: Sam Goldwasser SUBJECT: Re: Incandescent Lamp Life - overvoltage effects? DATE: 08 Dec 2001 19:26:06 -0500 ORGANIZATION: University of Pennsylvania NEWSGROUPS: sci.optics Rather than going into everything about lamp life and the distinction between halogen and normal incandescent lamps, perhaps first see the light bulb FAQ at: http://www.misty.com/people/don/bulb1.html Halogen lamps behave somewhat differently since the halogen cycle only operates at high envelope temperatures. There is also a newsgroup devoted to lighting related issues: sci.engr.lighting which may be more appropriate for these questions. --- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/ Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm | Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html