Lightbulb notes

From Helpful
Jump to: navigation, search

Lightsource types

Technical side

Incandescent and halogen lamps

Gas discharge lamps (arc discharge, glow discharge)

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me)


Carbon arc lamps

Fluorescent lamps

On ballasts

Mercury and sodium vapor lamp

Metal halide lamp

Neon glow lamps

Nixie tubes

Further notes

VFDs

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me)
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 little text-shaped masks backlit with LED, but look a little different from 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

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 (typically glass, often rectangularish because of what they contain) because air would make them stop working.

They are ~30V devices (order of magnitude), so need their own voltage supply, and also a dedicated controller.

The segments are multiplexed to need fewer control wires - so yes, they are blinking, though it's less noticeable than LEDs because of the phosphors.


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.



LED

On flickering

On dimming

EL wire

Product side

The efficiency question

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me)

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"

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, or tell me)

Yes, but only really for halogen bulbs, and then only a subset of them.


When?

In the realm of lightbulbs, halogen bulbs are one of just a few types that specifically uses quartz glass envelopes, because quartz can deal with higher pressure and higher temperatures. This setup happens to be a little more fragile to other things - see below.

For context, note that some designs with quartz use an additional regular-glass envelope around the quartz envelope (in part as a buffer to protect against sudden large temperature differences), in which case the below doesn't apply.

Also apparently applies less to a lot of professional high-powered lighting, in that much of that uses hardglass.

...but unless you can reliably tell, it's good habit / rule of thumb to not touch anything that looks halogen.


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. 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.

Because of crystal properties of quartz, this will easily make it look cloudier, which is not very useful in a lightbulb.

Devitrification by itself barely affects bulb life, though.


The larger issue is that the fat and protein from your fingers could create hot spots - which puts a temperature differential on the glass while it heats, and thereby an amount of stress while it heats, probably breaking it sooner, sometimes much sooner. (so it's partly just about the higher temperatures, though the surface of quartz probably doesn't help(verify))

In theory, a little oil may just burn and sputter off soon enough. The issue is that in other cases, it could sort of etch itself in.