Lightbulb notes

Lightsource types

Technical side

Incandescent and halogen lamps

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Incandescence in a wider sense means "glows primarily because it's hot".

Incandescent lamps are a low-resistance wire that, with enough voltage, passes enough current and becomes hot enough to radiate a broad band of EM in (and beyond) the visible spectrum. (you can choose the material and thickness to work at human-safe voltages, but we mostly know this for mains-voltage variants).

In air, such a wire 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. While more controlled, it turns out that this evaporation is still 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. Both argon and nitrogen are common, cheap, and harmless gases. (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 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 even if you put its peak in the visible spectrum, you also similar amounts of power emitted outside of it - probably most in (near-)infrared, including 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, compact fluorescent, and LED lighting became 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, because logarithmic-ish brightness-for-power means you would probably turn it down a lot. (That said, halogen lasts longer than typical incandescent so your expectation might not be violated).

See also:

• https://en.wikipedia.org/wiki/Incandescent_light_bulb
• https://en.wikipedia.org/wiki/Halogen_lamp

Gas discharge lamps (arc discharge, glow discharge)

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VFDs

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larger-segment VFDs. The wires in front are the cathode filaments(verify)

dot matrix VFD

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

The efficiency question

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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"

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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.