Lightbulb notes

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Lightbulb types

Technical side

Lightbulb sockets

Edison screw

Typical for lightbulb/pear shapes. The number is the diameter in mm.

Most common are:

  • E27 - common large screw variant
  • E14 - common small screw variant

There are a handful of other diameters in use


See also: http://en.wikipedia.org/wiki/Edison_screw#Fittings

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 of these are IEC 7004


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

  • GU10 - pins with widened end that lock bayonet-style (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.


Larger variants like G23 and G24 are used in office lighting.


There are quite a few variants of these G-number bases, which vary in:

  • base shape
  • pin distance (between center and center)
  • pin thickness and length
  • pin shape (round/flat)

The number specifies the pin distance.


A few details are impled by the letters. For example, GZ bulbs use dichroic glass, which dissipate most of the heat so lets out most of the heat at the back. Beyond that, there are associations to be gleaned from extra letters (G, GU, GX, GY, GZ).

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 rear/socket, GZ does not.


  • GY6.35, G8, or G9 are more frequently JCD type. G9 is often mains, G6.35 is often low-voltage



JC, JCD

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 [1].



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 may need a stupider transformer, or just one designed for lower draw - or just attack more lights on a single adapter.



Other notes

See also DIY_optics_notes#Stage_lighting.


See also