A Question About Bulbs.

[coominya]

I just picked up this fiber optic light source to allow some top illumination, etc.








The bulb is supposed to be a 15V 150 Watt, but it's not...

This is what it's supposed to have.



And this is what is actually in it. A household down light I presume.




So instead of 15V 150W
I have one 12V 50W

Shall I use it until the new bulb arrives from Hong Kong in a MONTH or so, or is it wise to just wait? It's pretty bright as it is, but I assume that the rheostat should not be pushed too high if using the current bulb.

[PeteM]

Assuming you have a voltmeter, might want to see where the dial is for 12 volt max output. Don't go past that and your current bulb should be OK.

I'm a bit surprised you had to pay that much and wait that long. Might not be in stock, but this was Google's first listing for that part number: https://lamphouse.proflamps.com/en/Prod ... F/p/14150/ There are probably cross-references you could check at a place like Don's Bulbs (website).

[coominya]

I'll check the voltage, and no I didn't pay that much, that's just a picture.

[75RR]

Assuming you have a voltmeter, might want to see where the dial is for 12 volt max output. Don't go past that and your current bulb should be OK.

Go a little lower yet and you can extend the life of your bulb by a substantial number of hours.

[apochronaut]

Generally speaking, Chinese and Hong Kong value bulbs are poor value. Some of the ones manufactured to a name brand company's specs., may be pretty good but I have used quite a few brandless ones and they tend to fail prematurely. The halogen ones develop hot spots and large areas of tungsten deposition rapidly and get dim and clouded quickly.

You have to watch out for the maker of the bulbs on line. Retailers will sub. inferior bulbs for the genuine article often, if they don't specify the brand. They will give for instance an Osram # but supply a Chinese bulb of similar design. Sometimes the filament isn't even the same shape as the original design called for. Look for Sylvania,Osram,Philips,GE, Ushio. Hosobuchi, Toshiba, Eiko.

[billbillt]

"Shall I use it until the new bulb arrives from Hong Kong in a MONTH or so, or is it wise to just wait?"

By all means use it till the proper one arrives....

BillT

[coominya]

Thanks for the replies. I haven't actually ordered the new one yet, $20, but I have dozens of these 12V halogen bulbs laying around so I might just see how the one in there goes. They have been basically throwing them away here since the energy saving fat took hold. Why spend good money and wait 2 months for delivery of a bulb that has a mere 50 hour rating?

[75RR]

Why spend good money and wait 2 months for delivery of a bulb that has a mere 50 hour rating?

If you run it below the max voltage you can extend its life substantially.

Using the formula above I calculate that running the 15v - 150w - 50hour bulb at 12v (admittedly less brightly)* you can extend its life from 50 hours to around 900 hours.
*Whether it would still be bright enough for your needs only you can say

Here is the formula again + the calculator steps ...
The figures are for a 12v - 60w - 100hour incandescent bulbs running at 10v.

[MichaelG.]

Here is the formula again + the calculator steps ...
The figures are for a 12v - 60w - 100hour incandescent bulbs running at 10v.

That's a very useful formula for 'normal' incandescent bulbs ... but I must mention one serious caveat

Tungsten Halogen bulbs were designed to run hot, and under-running them can [perhaps counter-intuitively], reduce their useful life; because the 'cycle' is not activated.
https://www.litetronics.com/how-does-th ... ycle-work/
https://en.wikipedia.org/wiki/Halogen_lamp

MichaelG.

[Hobbyst46]

Here is the formula again + the calculator steps ...
The figures are for a 12v - 60w - 100hour incandescent bulbs running at 10v.

That's a very useful formula for 'normal' incandescent bulbs ... but I must mention one serious caveat

Tungsten Halogen bulbs were designed to run hot, and under-running them can [perhaps counter-intuitively], reduce their useful life; because the 'cycle' is not activated.
https://www.litetronics.com/how-does-th ... ycle-work/
https://en.wikipedia.org/wiki/Halogen_lamp

MichaelG.

Michael, thanks for point out this important information and link!
To cite Wikipedia:"Tungsten halogen lamps behave in a similar manner to other incandescent lamps when run on a different voltage. However the light output is reported as proportional to V^3, and the luminous efficacy proportional to V^1.3 [ref 17]. The normal relationship regarding the lifetime is that it is proportional to V^(− 14). For example, a bulb operated at 5% higher than its design voltage would produce about 15% more light, and the luminous efficacy would be about 6.5% higher, but would be expected to have only half the rated life. "

The problem is, that a consumer, including microscopists, cannot tell the temperature at which the light bulb is running. So I would expect that the power supply of a halogen lamp for microscopy, at least, to bear a "minimum" setting mark, so the light intensity would change from zero (when turned off) to a decently bright level (when turned on) as step function, not gradual brightening from very dim to bright. Is this the situation with power supplies for halogen microscope lamps ?

[75RR]

Tungsten Halogen bulbs were designed to run hot, and under-running them can [perhaps counter-intuitively], reduce their useful life; because the 'cycle' is not activated.

I believe running a volt or two under the designed voltage would both extend halogen bulb life and allow the bulb to maintain its cycle. Halogen bulb power supplies come with dimmers after all.
In fact an important tip to avoid shortening bulb life (both incandescent and halogen) is to avoid turning them on and off at high voltage.
It is advisable to dim down before turning a bulb off and slowly increase the voltage when turning a bulb on.

[coominya]

an important tip to avoid shortening bulb life (both incandescent and halogen) is to avoid turning them on and off at high voltage.
It is advisable to dim down before turning a bulb off and slowly increase the voltage when turning a bulb on.

Good tip. I was just experimenting with that very practice tonight, wondering if it might prolong their life, and now you have confirmed it.
On the lowest setting the light source I bought is VERY bright when positioned over a subject, since I can position the tip of the fiber cable within a few mm.

[Hobbyst46]

For some fiber optic lamps (Dolan Jenner for example) collimating lenses are available (push-on type) that enable to modify the light beam.

[MichaelG.]

It is advisable to dim down before turning a bulb off and slowly increase the voltage when turning a bulb on.

That reminds me : Back when 35mm projectors were popular, I recall seeing a simple design for a 'soft start' for the lamp.
... If I can find the schematic, I will post it here.

MichaelG.
.

Edit: Here's one for 12V 50W lamps:
https://www.electroschematics.com/8088/ ... gen-lamps/

[coominya]

For some fiber optic lamps (Dolan Jenner for example) collimating lenses are available (push-on type) that enable to modify the light beam.

lol, I wondered what that little lens attached to the end of one of the coily pipes was, it seemed useless for what I wanted to do as it only widened the beam. I just went over and discovered that by loosening the set screw and moving it out the beam gets narrower and narrower.

I owe you one HB, I owe all you guys a lot actually