Lightbulb notes

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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, fix, 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



On flickering

On dimming

EL wire

Product side

Lightbulb sockets

Edison screw

Edison screw (E27, E14)

Typical for lightbulb/pear shapes. The number is the outer diameter of the metal screw part in mm.

There's quite a few of them, but by far most common are:

  • E26/E27 - common large screw variant
Apparently there's a correlation where E26 is for 120V countries and E27 for 230V countries(verify), but they're close enough
  • The more common small variant is usually E14 (Europe) and E17 (US)

There are a handful of other diameters in use, e.g.

E10 (miniature) in older flashlights, indicator lights, bike lights
uncommon now in all those uses, because e.g. LED is more efficient than incandescent
E39/E40 (giant/'mogul') in industrial / older stage lighting

See also:

bi-post / bi-pin

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, fix, or tell me)

Many bi-post are IEC 7004 (verify)

You may like overviews from image searches for terms like light bulb socket types diagram

The number specifies the pin distance. Each distance tends to have a unique socket/plug design, in part to make them more easily identifiable.

GU10 (230V MR16), GX5.3 (12V MR16 bulb)
G9 with its loops

Variants with smaller distances are typically small spots (classically halogen), for example:

  • GU10 - pins, 10mm distance, widened bayonet-style end (seems to be one of only a few G variants that has that bayonet)
  • GX5.3 - pins, 5.33mm distance
  • G4 - pins (4mm distance, thinner)

These may be easy to find in supermarkets and such.

  • G9 - flat loops, 9mm between the centers of the loops

Larger variants like

  • G23 and G24 are used in office lighting.
  • G53 is used e.g. in larger PAR spots

A few further details/associations are specified by the letters, e.g. G, GU, GX, GY, GZ.

For example, GZ bulbs use dichroic glass, which dissipate most of the heat so lets out most of the heat at the back.

Power and beam angle may wel be specified [1] though have some inconsistencies in specification.

While endless combinations between socket, bulb, and voltage could exist, there is a lot of consistency in what is actually produced, so in practice most most further details are (only) implied from most specific references being unique(verify).

For example:

  • GU4 are often 12V MR11 bulb
  • GU5.3 are often a 12V MR16 bulb
  • GU10 are often mains-voltage MR16 (as are various others with >7mm pin spacing)
GZ10 is like GU10 but does not have a beveled base, which means you can't use GZ10 in GU10 sockets (but can the other way around). The reason seems to be a heat/safety restriction: GU reduces heat to to the rear/socket, GZ does not.
  • G6.35 (1mm thick pins)
  • GY6.35 (1.25mm thick pins)
  • GY6.35, G8, or G9 are more frequently JCD type.
G9 is often mains, G6.35 is often low-voltage


Refers to a shape - just the small halogen bulbs, no reflector. Can be 12V, 24V, or mains voltage.

Comes in a few base sockets, often one of G6.35, G4, G8(verify)

Apparenly frequently semi-permeable glass, which is why you shouldn't touch it with your oily fingers.

MR, Multifaceted Reflectors

MR (e.g. in MR11, MR16) refers to a Multifaceted Reflector, which produces a more focused beam than simple parabolic reflectors. (see also PAR, which is more specifically an anodized reflector)

MR bulbs are mostly associated with G-style bases, including GU10, GX5.3, and G4.

The number in MRsomething is the bulb diameter - in eighths of an inch, so MR16 bulbs are 5.1cm in diameter, MR11 are 3.5cm.

The combinations of diameter and socket aren't unique - which means it's fairly easy to walk into a store and buy a MR16 and discover you needed one with a GU10 and GU5.3 base and got the other.

You sometimes see specifications of diameter as well as power and beam angle - see [2].

On voltage

Different MR bulbs may be 12V (most) or higher voltage (some), so never blindly assume.

12V may still be AC, though are often DC in practice.(verify) LED-based MR-series often won't care since they need to rectify anyway.

Some of the 12V (switch-mode) adapters designed for a string of halogen MRs will not like the low power draw of LED variants. You need a transformer that is not trying to be clever, one designed for lower draw, attach more lights on a single adapter, or get one designed with LEDs in mind.

Other notes

See also DIY_optics_notes#Stage_lighting.

See also

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, fix, or tell me)

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

In the realm of lightbulbs, halogen bulbs are one of a few that specifically uses quartz glass, because quartz can deal with higher pressure and temperatures.

Note that some quartz designs don't need to, or use an additional regular-glass envelope around the quartz envelope (in part to protect against large temperature differences), in which case the below doesn't apply.

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.

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 clear 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 fat and protein from your fingers could create hot spots - which puts a temperature differential and thereby the amount of stress while it heats, probably breaking it sooner, sometimes much.

In theory, a little oil may just burn and sputter off soon enough - it's more that in some cases it could sort of etch itself in.