How do ceramic infared heat bulbs work and are they safe to stare at?
December 17, 2013 5:35 PM   Subscribe

I have a 150 watt ceramic infrared heat bulb similar to this one that I use next to my desk to help keep me warm. It produces no visible light, only heat. Sometimes I have the urge to stare at it, can it hurt my eyes from the infrared radiation, similar to how looking at a regular light bulb can hurt your eyes? I am also interested in how these bulbs work, and the type of infrared radiation they give off if someone can explain it to me.
posted by john123357 to Home & Garden (16 answers total) 1 user marked this as a favorite
There seems to be a well-established link between staring into infrared and developing traumatic cataract (google "glassblowers cataract"), but whether your lamp is strong enough I don't know.
posted by Namlit at 6:37 PM on December 17, 2013

According to the Wikipedia page, "Individuals exposed to large amounts of infrared radiation (like Glass blowers and arc welders) over an extended period of time may develop depigmentation of the iris and opacity of the aqueous humor, so exposure should be moderated." The amount of radiation given off by yours is miuch, much less and shouldn't be harmful.

The article also goes into detail about the workings of various types of infrared heaters.
posted by Johnny Wallflower at 6:39 PM on December 17, 2013

I don't know about your specific bulb, but it sounds similar to this one. The manufacturer's spec indicates that it's putting out EM between 2 and 10 μm, which is well past range of near-visible infrared that's supposed to be dangerous.

The danger with near IR (750-1400 nanometers. 1000 nm = 1 μm) is that it can be focused on your retina just like visible light. Since you can't detect it - and the retina doesn't have pain receptors - you might not notice exposure until damage had occurred. At the wavelengths listed your cornea should be absorbing the vast majority of the radiation before it reaches your lens or retina.

Of course, letting your cornea absorb IR can also damage it, but it's not being focused on the tissue like it would be on your retina and the cornea is quite good at healing. Infrared emitters in these wavelengths certainly exist which can damage the various components of your eye, but since your bulb isn't an infrared laser - and it isn't plastered with eye-safety warnings - you probably aren't in any danger.
posted by figurant at 6:48 PM on December 17, 2013

Does this type of bulb actually produce infrared radiation since it produces no light? Or is it just a metal wire that heats up inside a ceramic casing?
posted by john123357 at 8:59 PM on December 17, 2013

Yes. All objects emit thermal radiation due to their temperature. Normal light bulbs reach temperatures so high that their thermal radiation is in the visible spectrum. Your infrared bulb emits only at lower (infrared) frequencies, which is why you can't see any light but you can feel it as radiant heating.
posted by mbrubeck at 9:28 PM on December 17, 2013

like Glass blowers and arc welders

Well, arc welders are exposed to quite a lot of ultraviolet, not just infrared.

Near-infrared can cause damage the same way visible light does, with the added difficulty that you won't reflexively blink or look away.

But yer typical ceramic heat lamp is going to be mostly emitting in the farther infrared, as figurant notes, and that's a lot less dangerous (the googles suggest that it's unclear whether it's dangerous at all at these levels, eg, eg).

My non-medically-knowledgeable understanding is that in order to damage your eye you'd need to fix your gaze on the bulb for long periods and do this over a span of time. And possibly use a larger/hotter bulb and avoid blinking.
posted by hattifattener at 9:53 PM on December 17, 2013

Is it the heat from the bulb or the invisible infrared light that can damage vision? Would putting it 4 feet away and then staring at it be okay?
posted by john123357 at 9:56 PM on December 17, 2013

The heat and the infrared radiation are the same thing, not two different things.
posted by ssg at 10:10 PM on December 17, 2013 [1 favorite]

Yeah. To the best of my knowledge, the way that far-infrared damages your eyes is just by overwarming your cornea. Your cornea doesn't have as much blood flow as, say, your skin, so it can't deal with external radiant heat as well.

I don't like to say "don't worry, you'll be fine" because I'm not an expert and maybe I'm misleading you, but I'm pretty sure that, as far as idly gazing at a 150W heat bulb goes, you shouldn't worry, you'll be fine. It's no worse than, say, staring at a campfire.
posted by hattifattener at 10:28 PM on December 17, 2013

The heat and the infrared radiation are the same thing, not two different things.

Yup. Heat can transfer from one thing to another in the form of radiation (infrared light), conduction (touching it), or convection (warming the air next to it.)
posted by sebastienbailard at 10:29 PM on December 17, 2013

Is it the heat from the bulb or the invisible infrared light that can damage vision?

It's the heat in the tissues of your eyes caused by their absorption of the invisible infrared light, whose emission is itself caused by the heat in the bulb.

As a child, I laboured for years under the misapprehension that infrared was this special kind of light that is in some mysterious way "heat". Not so. Heat is nothing more or less than atoms and molecules just jiggling about, and absorbing any kind of light will make them do that.

If something absorbs infrared light, it will heat up. If something absorbs visible light, it will heat up. If something absorbs ultraviolet light, it will heat up. When you feel the sun's warmth on your skin, you're feeling your skin's reaction to absorbing all of whatever light doesn't bounce off it, not only the infrared frequencies.
posted by flabdablet at 8:28 AM on December 18, 2013 [1 favorite]

Is staring at this 150 watt heat bulb more or less dangerous than staring at at 150 watt incandescent light bulb?
posted by john123357 at 8:44 AM on December 19, 2013

It very much depends on how you define the risk, or danger. Staring at a normal light bulb makes you realize very soon that it's not a good thing to go on with it, and you stop. Staring at a heat bulb delays that effect since you can't see the light, so your preventive action will be compromised. I'd call that "more dangerous."

How dangerous staring at either bulb is per time unit will obviously depend on their respective wattage.

I hope this question is hypothetical.
posted by Namlit at 9:00 AM on December 19, 2013

I'd expect it to be less dangerous, both because the emission source is far more diffuse (staring at the heat lamp won't make a nicely focused image of a small high-temperature filament on your retina) and because the bulk of your eye is less transparent to infrared light than to visible light.

There is really nothing to know safety-wise about a "ceramic infrared heat emitter" that doesn't also apply to any comparably hot thing of comparable size; the infrared rays it emits are a straightforward consequence of the temperature of its surface, not some special kind of emanation from its mysterious electrical innards. If you're far enough away from this thing that your face isn't feeling uncomfortably toasted, your eyes won't be taking any more damage than they would from looking at, say, a hot cooking pot or kettle.
posted by flabdablet at 9:24 AM on December 19, 2013

I am also interested in how these bulbs work, and the type of infrared radiation they give off if someone can explain it to me.

They work by converting electrical energy to heat energy using resistance wire enclosed in ceramic, and the infrared radiation they give off is pretty much black-body thermal radiation.
posted by flabdablet at 10:45 PM on December 19, 2013 [1 favorite]

Incidentally, apart from the "enclosed in ceramic" part this is exactly the same way ordinary incandescent light bulbs work. Both are simple resistance heaters emitting black-body thermal radiation, but because the incandescent lamp's filament operates at a much higher temperature its black-body emission spectrum's peak is in the visible range.

An incandescent bulb's filament is far smaller and lighter than the ceramic-enclosed resistance element in an IR emitter with the same power rating, and this is why it achieves a much higher temperature when converting electrical energy to heat even though both the electrical resistance and power consumption are identical.

Halogen bulbs work the same way as well, but their filaments are smaller and lighter still and run even hotter, which is why their light looks bluer. A larger proportion of the "tail" of a halogen bulb's black-body spectrum falls inside the visible range compared to a standard incandescent's, accounting for the halogen bulb's improved lighting efficiency, but a fair amount of it falls outside the visible range on the upper side as well: halogen bulbs emit enough ultraviolet that you can actually get sunburn from them. Best not to stare at one of those.
posted by flabdablet at 11:18 PM on December 19, 2013

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