Typical for lightbulb/pear shapes. The number is the diameter in mm.
There's quite a few of them, but by far most common are:
- E26/E27 - common large screw variant
- Apparently E26 is for 120V countries and E27 for 230V countries, but they're close enough
- E14 - common small screw variant
- E10 - flashlight, bike light
- getting less common, because e.g. LED is more efficient than incandescent
There are a handful of other diameters in use (christmast lights, industrial)
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.
The number specifies the pin distance. Each distance tends to have a unique socket/plug design, in part to make them more easily identifiable.
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.
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.
Once you get to products, there are more variations, and more is specified, e.g. Power and beam angle can be specified .
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).
- 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.
- 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 .
- 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.
See also DIY_optics_notes#Stage_lighting.