Lightbulb notes: Difference between revisions
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Incandescent lamps are | Incandescent lamps are | ||
a low-resistance wire that, with enough voltage, becomes hot enough to radiate EM in the visible spectrum. | a low-resistance wire that, with enough voltage, becomes hot enough to radiate EM in (and beyond) the visible spectrum. | ||
In air, the filament would oxidize | In air, the filament would oxidize quickly and burn out too quickly for this to be very useful. | ||
Putting the filament in a vacuum wouldn't oxidize, but instead evaporate. | Putting the filament in a vacuum wouldn't oxidize, but instead evaporate. | ||
While controlled, it turns out that this evaporation is faster than necessary. | While more controlled, it turns out that this evaporation is faster than necessary. | ||
So the refined form of incandescent lamps contain an inert gas ''instead'' of oxygen, typically argon (plus some nitrogen to help avoid arcing), | |||
as this makes for slower evaporation of the filament than in a vacuum - and both argon and nitrogen are common, cheap, and harmless gases. | |||
{{comment|(Krypton and xenon isolate better than argon, but are pricier, so are only used for designs that actually need that)}} | |||
'''Halogen lamps''' are a variant on incandescent, the name referring to the [https://en.wikipedia.org/wiki/Halogen_lamp#Halogen_cycle halogen cycle] redepositing some of the freed filament metal back onto the filament. | |||
This requires a halogen gas, and for the bulb to burn about twice as hot as is even practical for most incandescent, which is part of why these are usually higher-power bulbs and associated with bright lights (and also why they may use quartz glass, which deals with higher temperatures). | |||
Pretty much all variations of incandescent is inefficient in that they are so wide spectrum that, when you want a lot of it in the visible spectrum, you also similar amounts of power emitted in near infrared, i.e. as heat. | |||
While in cold climates this may help heat your house electrically, in moderate and warm climates that heat is a significant waste product (that affects your cooling bill) that has been avoidable since fluorescent, CFLs, and LED lighting because practical (roughly in that order). | |||
Dimming incandescent bulbs extends their lifetime due to slower evaporation of the filament. | |||
Dimming halogen lamps actually ''lessens'' their lifetime ''when'' you dim it enough to stop the halogen cycle, which happens very easily due to logarithmic-ish brightness-for-power. (That said, halogen lasts longer than typical incandescent so your expectation might not be violated) | |||
Halogen can be a little more trouble, because even with the extra layer of glass you sometimes get enough temperature differential to have glass shatter. This tends to happen only with larger-powered ones in cold places, though, and lamps for specific purposes (e.g. car headlights) are typically engineered for it fairly decently. | |||
Halogen can be driven from AC (e.g. just a transformer) or DC. | |||
You generally want to drive them at full power, | |||
and if they're 12V variant you'll need a relatively beefy power supply (which can just be a transformer). | |||
If you don't know the rating, note that due to non-flat I-V curve, the resistance you measure cold is higher, and becomes a factor ~15ish lower at full power). | |||
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'''Gas-discharge lamps'''[https://en.wikipedia.org/wiki/Gas-discharge_lamp] are a larger family of designs. | '''Gas-discharge lamps'''[https://en.wikipedia.org/wiki/Gas-discharge_lamp] are a larger family of designs. | ||
What they share is that they sustain ionization of gas | What they share is that they sustain ionization of gas and passing current through that (a plasma), the ways different lamps use this to produce light are different enough to really call them different types of lighting {{comment|(Even when you ''don't'' count carbon arc lamps - which basically set air on fire, and are now rare)}}. | ||
{{comment|(And all are quite distinct from incandescent, where a conductive filament is heated to the point that the filament itself radiates. Being a black body style thing, this is wide-band, simple, and relatively wasteful)}} | {{comment|(And all are quite distinct from incandescent, where a conductive filament is heated to the point that the filament ''itself'' radiates. Being a black body style thing, this is wide-band, simple, and relatively wasteful)}} | ||
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: but not visible to us | : but not visible to us | ||
* glow discharge is when enough current is involved in discharge that they start emitting a load of photons (often in the human-visible region) | * glow discharge is when enough current is involved in discharge that they start emitting a ''load'' of photons (often in the human-visible region) | ||
: for sensible voltages this is only practical/noticeable at lower pressures | : for sensible voltages this is only practical/noticeable at lower pressures | ||
: and lamps use gases more suitable than air | : and lamps that use this use gases more suitable than air | ||
* arc discharge is when the electrode becomes hot enough to also do thermionic emission, enough to sustain a a high-current arc {{verify}} | * arc discharge is when the electrode becomes hot enough to ''also'' do [[thermionic emission]], enough to sustain a a high-current arc {{verify}} | ||
:: which then becomes the dominant effect, and the properties of the gas are less influential | :: which then becomes the dominant effect, and the properties of the gas are less influential | ||
: current is higher, voltage is lower | : current is higher, voltage is lower | ||
Revision as of 14:41, 26 March 2024
Lightsource types
Technical side
Incandescent and halogen lamps
Gas discharge lamps (arc discharge, glow discharge)
Carbon arc lamps
High Intensity Discharge (HID)
Fluorescent lamps
On ballasts
Mercury and sodium vapor lamp
Metal halide lamp
Neon glow lamps
Nixie tubes
Further notes
VFDs
When you see displays that you suspect might be backlit LCDs, or maybe little text-shaped masks backlit with LED, but don't look like typical examples of either, look closer.
If looking close reveals a fine grid pattern (often hexagonal), they are probably Vacuum Fluorescent Displays (VFD) [1].
They can be seen as a cross between
- CRTs in why they light up (see also cathodoluminescence), and
- triode vacuum tubes in how they are driven:
- a phosphor-coated anode
- a cathode to generate electrons
- and a mesh grid inbetween to switch individual areas on or off
- in a low-pressure enclosure because air would make them stop working (typically glass, often rectangularish because of what they contain and for ease of production).
They are ~30V devices (order of magnitude), so need their own voltage supply, and a dedicated controller that controls that.
The segments are multiplexed to need fewer control wires - so yes, they are blinking, though it's less noticeable than LEDs because of the phosphor's persistence.
They frequently have a light blueish-green color (sometimes darker, using colored plastic in front), related to the choice of phosphor. Red, orange, and yellow also appear.
There may be filters in front for subtler colors, slightly better contrast, and sometimes varying color.
https://www.youtube.com/watch?v=PkPSDOjhxwM
LED
On flickering
On dimming
EL wire
Product side
The efficiency question
Lightbulb sockets
See Common_plugs_and_connectors#Lightbulbs
Other notes
On angle
See e.g. DIY_optics_notes#PAR_spot
"You shouldn't touch lightbulbs"
Yes, but only really for halogen bulbs, and then only a subset of them.
When?
In the wider realm of lightbulbs, halogen bulbs are one of a few types that specifically uses quartz glass envelopes, because quartz can deal with higher pressure and higher temperatures. Touching quartz has a few footnotes that apply to it more than to glass in general - see below.
Note that some designs with quartz use an additional regular-glass envelope around the quartz envelope - also in part as a buffer to protect against sudden large temperature differences - in which case this doesn't apply.
Also, apparently a lot of professional high-powered lighting uses hardglass, in which case it also doesn't apply.
...but unless you can reliably tell, it's good habit / rule of thumb to not touch anything that looks halogen, or to handle it via a cloth or whatnot.
Why?
When using quartz glass, there are two extra things that can happen.
One is devitrification, a change of the crystal structure from a more random to a more crystalline form. This is a more general concept, but in glass this happens more easily with higher temperatures, and/or when there is a nucleation center for a crystalline structure to start growing, which happens more easily when there are surface impurities. Like the oil from your greasy grabby hands.
Because of crystal properties of quartz, this will easily make it look cloudier, which is not ideal in a lightbulb, though also not necessarily the biggest worry, and devitrification by itself barely affects bulb life.
The larger issue is that the fat and protein from your fingers could create hot spots - bits that become higher temperature than the clean glass around it - which puts a temperature differential on the glass particularly while it's still heating, and thereby an amount of stress while it heats, probably breaking it sooner, sometimes much sooner.
In theory, a little oil may often just burn and sputter off soon enough. The issue is that in other cases, it could sort of etch itself in.