“18 watt OTT-LITE TrueColor tube is included and lasts for up to 10,000 hours
Energy efficient with low heat and glare illumination which helps reduce eyestrain”
Wonderful, right? Nice guy. However, Mom now lives in fear that the light and magnifying glass will line up just right and cause a light beam that will burn a hole in the quilt she is working on. I thought that was just for sunlight and little bugs on the driveway, but she’s convinced harm will come to her crafts.
Never heard of an Ott light before. But if it’s a halogen lamp, then that lamp will get quite hot. Halogen lamps have to – they only operate correctly if they’re running hot. At high temperatures the reaction that causes the tungsten to be plated back onto the filament (thu extending bulb life) operates. Otherwise, it doesn’t. Running a haslogen bulb at low temperatures is a waste.
The problem is that halogen bulbs can get so hot that cloth coming in contact with them can catch fire. This has especially been a problem with those torchiere lights, since cloth falling into or deliberatly placed on them (as an impromptu shade, or whatever) has a high probability of getting in contact with the bulb and maybe burning.
Of course, you’re not doing that – you’re using a magnifying glass to concentrate light onto your work surface.
When you use a magnifying glass to concentrate the sun’s light onto a piece of paper, or the campfire you’re trying to start, or a bug (you sadistic bastard), you’re concentrating the light from a source that 93 million miles away, but still too bright to look at. You can at least look at your halogen bulb.
BUT – you can still produce an image that is the same size as the bulb or smaller than the bulb on a piece of cloth. Can this cause it to burn? The answer, I think, is “maybe”. There’s a useful law in optics called the Raduiance Theorem that states that the number of photons per unit area per unit solid angle in an image cannot exceed that of the source*. Usually it’s lower, because you inevitably have losses. The point is that just because you make the image smaller than the object doesn’t mean that you’re going to get the image hot enough to burn things, if you start with a relatively low-power source. It does mean, though, that if you start out with a sufficiently hot source, you can. The surface of the sun, for instance, is hot enough to torch bugs. Similarly, the heat from a tungsten halogen bulb can demonstrably set cloth on fire (I haven’t done it myself, but there are plenty of reports), so conceivably the image of a tungsten halogen bulb can, too.
I think it’s not likely unless tyou work at it, personally. But if it’ll make her feel better, I seriously dobt that you’ll ever be in trouble with a fluorescent light source, or even a standard incandescent bulb.
*subject to other criteria as well. I assume you’re in the same refractive index, object and image.
I don’t know officially what kind of bulb it is but it’s the kind that has a bluish light to it, and stays relatively cool. Oh, “full-spectrum” I think. Does the 18 watts level make a difference?
That appears to be a screw-in fluorescent bulb. If it’s “Tru-Lite” it’s probably one with phosphors that make it look more like an incandescent bulb than old-style bluish fluorescent bulbs (the kind Tom Hanks rails against in Joe Versus the Volcano as sucking all the life out of you).
If that’s the case, you have absolutely no worries. Touvch the bulb when it’s on – it should be quite cool. And y the Radiance Theorem, it’s not going to be any hotter on your cloth.
My wife has an OTT light with magnifier. Tell mom no worries, she isn’t going to bun a hole in anything. My wife loves her OTT light for her needle work and hasn’t burned a hole in any of it.
There’s a greater “risk” to her crafts from slowly bleaching out if she works on them in natural sunlight. Or from the moisture from just breathing on them.
Why not take the most easily flammable material you can find, loose cotton, nice dry tinder or something like that, and let her try to ignite it? Or just char or discolor it lightly. Adjust the lens so that it creates the smallest and brightest patch of light. If you have a stronger magnifying glass than that of the lamp, try that too.
Show her that, even in the worst case scenario, nothing happens. If this still won’t dispel her fears, you know it’s time to cut her off from watching too much FOX News…
For future reference I’ve seen a halogen light and focusing lens burn paper unintentionally. It took like 15 minutes, so there was no sign of what was to come, when they set up the situation. It was the focused light and not the hot bulb that caused the burning.