Incandescent lamps technical resources & information

For those of you who want to know more about incandescent technology as it applies to flashlights, I have created this technical resources & information thread. I, and I hope others, will add to it as time goes on.

I will start things off with my favorite resource so far:

Osram's Tungsten Halogen Low Voltage Lamps Photo Optics publication.

There is some truly excellent information in this small book, including lamp physics, construction of low-voltage tungsten halogen lamps, stuff about color temperature, black bodies, luminous efficiency, and so on, and electrical characteristics of bulbs, lamp life, and proper handling and safety, and much more.

Next up is the place where, back in the day, all of us hotwire guys got our hands on the lamp re-rating formulas, which I will put here in black and white. In these formulas Vd is the design voltage, which you would get from the manufacturer, along with the design lumens, design current, design power, design bulb life etc. Va is what you are actually going to apply to the lamp - the applied voltage. The re-rating formulas all consider the ratio of Va to Vd (or its inverse in the case of lamp life), and apply powers to this ratio to predict re-rated lumens, life, current, power, etc. The prediction is most accurate for small deviations from the design voltage. The further away you re-rerate, the less accurate the re-rated prediction. The re-rating formulas are as follows:

Re-rated Lumens = (Va/Vd)^3.5
Re-rated Current = (Va/Vd)^0.55
Re-rated Life = (Vd/Va)^12

From:

Welch Allyn's Miniature Halogen Lamps publication.

I will also add to the re-rating formulas, the 65 percent rule of thumb to translate from "bulb lumens"--the number published on something like the Welch Allyn website, and "torch lumens"--the actual amount of light making it out the front of your flashlight. This percentage may seem to conservative, but it has been verified both via experience and with an integrating sphere. See my bLu vs. tLu: IS confirms 65% conversion factor thread.

OK. That's all for now. I will add to this first post as we come up with more technical resources that are available online.

Subscribed!

Awesome link and info!! :twothumbs

I've ALWAYS wondered why some bulbs have the point at the bottom (WA - Welch Allyn?) and some at the top (SureFire bulbs - Carley?).


And now I know......

Good to see you, Jim!

I'm suddenly feeling nostalgic as I remember the discussions around here regarding these formulas (formulae?.. haha).

However, instead of just desiring to recapture the exciting feeling of the old days, I'm going to follow the links you've provided to finally get a deeper understanding of bulb theory, and other stuff.

Thanks for posting, and best regards!


John

John,

How the heck are you? Good to see you around as well. I hope you enjoy the two documents. I think they're pretty neat, but then I've always had a fondness for good incans.

Hi Jim,

What a comprehensive info about incan bulb. thanks your sharing!

For the formulas, I have a newbie question: (Assume I use formulas with battery power source (e.g. 2xli-ion))

Is Vd same as working/under-loaded voltage of the battery which is considered by manufacture?

If so.. when re-rating(e.g. Lumens) a high current bulb, e.g. 7V5A, first I need to know the under-loaded voltage (2x2.7v) of Va (Va = 2x3.7v), so the bulb is underdriven by 5.4v, actually Va is 5.4v not 7.4, right?

Thanks

Thanks your sharing!

cenz said:

Hi Jim,

What a comprehensive info about incan bulb. thanks your sharing!

For the formulas, I have a newbie question: (Assume I use formulas with battery power source (e.g. 2xli-ion))

Is Vd same as working/under-loaded voltage of the battery which is considered by manufacture?

If so.. when re-rating(e.g. Lumens) a high current bulb, e.g. 7V5A, first I need to know the under-loaded voltage (2x2.7v) of Va (Va = 2x3.7v), so the bulb is underdriven by 5.4v, actually Va is 5.4v not 7.4, right?

Thanks

Click to expand...

Vd is the design voltage specified by the manufacturer, or just it's normal operating voltage that you have experience with.

Va is the applied voltage at the lamp, which is the voltage under load of the battery pack, minus any voltage drops between the battery pack and the lamp due to resistances.

In your example, if the two batteries are only supplying 2.7 volts at 5 amps, and your bulb is quoted at 7 volts, then your Va will be 5.4 volts--except it will be higher because the current draw will be lower. If you got 2.7 volts from a discharge curve, like from SilverFox's threads, and you looked at 5 amps because that's what the bulb draws at 7 volts, then you have the wrong current, because you're at 5.4 volts. You really kind of have to measure the voltage with a DMM to really know. (Plus, voltage under load changes as the battery pack discharges.)

But, yes, if you can find the Va, then you use it in a ratio with the design voltage (7 volts in this case).

I hope that helped! Let me know if you have more questions!