Test Halogen light bulb for wattage?

Light bulb filaments behave very non-ohmically. They'll show a very low resistance when cold or at lower currents, then a much-increased resistance at their operating temperature. That makes it very hard to tell what you've got from a cold ohms reading.

Pretty much the way you tell is by putting its rated voltage across it, measuring the current that flows then once it has stabilized, and multiplying the volts by the amps to get the watts.

If you have a handy little gizmo like the Kill-A-Watt, you plug the lamp into it, turn it on, and read the watts.

What kind of base does this halogen bulb have? You might have the option of finding something that will run cooler and use less juice, like an LED replacement using the same base.

 

A19 refers to the shape and size of the bulb. Any bulb that has the weird, arbitrary, familiar light-bulby shape, and is 19/8" across at the widest point, is an A19 bulb.

If it has a base that is 26 mm across (not eighths of an inch!) with the usual Edison screw-in threads, that's an E26 base.

https://blog.lightingsupply.com/blog/a19-bulb-vs-e26-bulb-whats-the-difference

So a bulb with an E26 base and A19 shape is pretty much the canonical "light bulb", the one that appears over anybody's head when they're having an idea.

And yes, there are lots of other options around with that shape and that base. You could put in an LED bulb that gives you the same amount of light as a 60-watt incandescent, and it'll use about 6 watts. Or put one in that gives you as much light as a 100-watt incandescent, and it'll use about 10 watts. Neither one will be anywhere near exceeding the limits of your fixture.

Aside from saving energy, this is a great way of getting more light out of old fixtures than you'd be able to get with the maximum wattage incandescent bulb they could safely accept.

 

Sounds like a good excuse for an amp meter probe.

Bob Wilson

 

Sure, but the needed toy count starts clicking upward soon enough.

Maybe you start with your amp meter probe.



But then, hmm, the cord to your light fixture has the gozinta and gozouta wires right next to each other. You can't just put your clamp over that, they'll cancel and always read zero. So are you going to slit your lamp cord and pull the two sides apart, so you can get your clamp around just one of them?

Who wants to do that? So now your toy list needs a clamp probe line splitter.



Before you know it, you've accumulated more toys than you'd have if you just had one Kill-A-Watt and plugged the lamp into it, and read the watts off.

 

Halogen bulbs don't burn any hotter than ordinary incandescent bulbs of the same wattage and configuration. The past fire problem with halogens was in 300 watt halogen torchiere floor lamps, which have a physically smaller lamp than ordinary A19 bulbs, and were susceptible to falling over and contacting flammable material.

The halogen A19 lamps I used, before CFLs became a thing, were actually (just slightly) cooler than equivalent incandescent bulbs. Being slightly more efficient (and whiter), a 52 watt halogen was equivalent to 60 watt regular incandescent. We also had some 75- and 100-watt equivalents, but I don't recall their actual wattages. They also lasted longer, probably about 3X.

There should be no problem in turning it on for a couple minutes to see how bright it is. If similar to a regular 60W bulb, then there shouldn't be a problem leaving it on.

If thriftyness is a consideration, then THROW IT OUT! and replace with a modern LED lamp. Those A19 halogens where a first minor step towards energy efficiency. CFLs saved far more, then LEDs did even better.

Using "free" incandescent or halogen lamps is very non-thrifty, because the energy to power them quickly exceeds the purchase price of good new LEDs.

 

For years I had one of those once-ubiquitous halogen desk lamps with the 'stylish' counterbalance mechanism (it was a gift).



It had a small capsule halogen bulb, and it did not have the disc of greenish glass that some of those fixtures had, below the halogen capsule, which was used partly (I later learned) to filter out the UV light that was given off generously by the halogen capsule.

It took me a surprisingly long time to figure out why my face always felt sunburned after working a long time at my desk. Once I did, I got rid of that desk lamp.

 

Well, like the thing Einstein almost said, it's as simple as it can be, just not simpler.

Wattage is the product of voltage times current. So you put the thing on its rated voltage, measure that with a voltmeter, measure the current at the same time with an ammeter, multiply the volts by the amps and boom, watts.

A voltmeter has probes you can just poke across something, easy. An ammeter has to be put in the current path, so as a practical matter you'd end up unscrewing something in your light fixture to wire the ammeter in, or wire up a plug and socket you can put between your fixture and the wall that diverts your current through the ammeter. Or you can use the kind of clamp probe shown in #6, but even then you still have to separate the two wires in your lamp cord, or plug it into the kind of splitter gadget also seen in #6.

So that's what makes a little gizmo like the Kill A Watt (also seen in #6) so handy. You plug it in the wall, plug your lamp into it, and it measures both the voltage and the current at once and multiplies them for you and shows you the watts.

Thumbs up on the LED. I'm sure you'll enjoy the 1600 lumens of light. And only using 14 watts. And probably the 7 to 13 year lifespan too.

(It's getting insane. I don't replace lamps because they burn out anymore. I use them several years and then replace them because somebody brought out new ones that'll give me more light from the same fixture, or better color rendering, or something, or just look nicer, like the filament-style LEDs. Then I take the old ones to the Re*Store.)

 

As for your fears of halogens being too hot, I should note that in this A19 form factor, halogens have an inner quartz capsule that is extremely hot. In the infamous hot torchieres and desk lamps, this quartz capsule was bare, but in A19s, it is surrounded by a larger and cooler glass shell.

The Kill-A-Watt meter shown in Chap's post is very easy.

Alternately, for standard incandescents in the 40-150 watt range, just "eyeball" by comparing their light outputs to other known bulbs. A visual version of an automotive "butt dyno". Not perfect, but this should be close enough. Halogens are very close cousins to traditional incandescents. If their light outputs match, then the halogen's wattage should be 28% (**) less than a 'standard' traditional incandescent.

The "eyeball" comparison won't work for CFL and LED lamps.

(**) 28% for recent products, maybe just 15-20% from some old products predating current law.

 

Also, most smartphones contain a light sensor, and there are lots of little apps for doing nothing but show the raw readings of the various sensors on the phone. (It seems to be a pretty common answer to people's "what should my first try writing a smartphone app be?" question. I installed one called Sensors Sandbox you can find on f-droid.)

So that's an easy way you can do a more quantitative, less butt-dyno-y comparison of two light sources.

For all I know, you might need some extra math to convert the raw sensor reading to the kind of calibrated number a photographer or architect would want. But for just asking "is this bulb brighter than that one?" the raw number is probably quite enough.

... which also acts as a UV filter.

If the outer glass shell breaks, the halogen bulb will still work (unlike the non-halogen incandescents). But your dermatologist might prefer that you stop using it then.

 

I don't even have any 'normal' light fixtures on the ceiling anymore. All have been replaced by thin flat surface-mount LED fixtures that have the control electronics sticking up inside the junction box. Very clean looking, no more ugly glass globes or covers from the ancient era. Nothing to gather dust or dead flies, or to be struck by very tall heads or swinging arms or flying kid's toys.

My biggest problem was that the available products would fit into "most" 4-inch junction boxes (or larger). But my house had the ones they didn't fit. I ended up laparoscopicly (i.e. through the ceiling hole from below, destructively, in pieces.) removing the junction boxes, and replacing them with re-work junction boxes with sufficient interior size. The one box directly underneath a fire sprinkler pipe was gingerly removed from above, in the attic, because I didn't trust that my laparoscopic method wouldn't break the pipe.

 

Not all glass globes are ugly*, and I've got a bungalow built in 1929, so with a little work one can find modern fixtures and globes that look approximately right.

The one place I've gone shamelessly newfangled is the unfinished basement, which never had much attention to lighting in the original design, and where the joists are low enough I've no desire to hang anything lower (other than the unavoidable plumbing and ductwork).

I got a roll of that 5050 SMD LED adhesive ribbon, and some wide metallic tape (as used for ducts). I can press a length of the aluminum tape along the bottom edge of a joist (and a bit up the sides) and stick a bit of LED tape right to the aluminum tape for heat dissipation, and do every second or third joist with a few short lengths of this spread out along the length of the joist, all wired back to a 12 volt 60 watt wall wart plugged in at the ceiling socket where the old bare bulb used to go. Result is basement very brightly and evenly lighted from everywhere, and nothing new to be struck by tall heads.

* On one trip to the Re*Store, I found a gorgeous ceiling fan whose light globes were stained glass. I called up an ex-sweetheart who has a house of similar style from the same period and told her about it, so she bought it and it's in her living room. I keep looking for another find like that one whenever I'm in there, but so far, lightning hasn't struck twice.

 

Sure, not all of them. Just lots them.

Those SMD LED ribbons look quite useful, but I haven't yet done much with them. Before I learned of them, several projects were done with earlier 12V LED modules: kitchen undercounter lighting; under-eaves (to minimize light pollution) very low power lighting for easier nighttime exterior inspections and eliminate any dark cover to hide; and lighting in a barn lacking utility service, powered instead by a small solar panel and battery. The later has been invaluable for midnight calving issues. If done today, these ribbons would do it all, and probably provide more lumens/watt than the items I used.