Does anyone know the light property differences between halogen PAR20 & GU10?
I am hoping that this is an accurate question as I am not sure that I am comparing apples to apples.
It seems that GU10 is a bulb base type and PAR is a type of bulb, that can have different base types (ie edison).
Can somone please shed some light on this?
It's a matter of size: a PAR20 (with an Edison Screw-base) is bigger/bulkier than a MR16 cup (with a GU10 twist-n-lock base). By the bigger optics (diameter 64mm versus 51mm), the PAR20 will have better beam characteristics (smoother spot on the wall) than MR16 lamp with a mains voltage halogen capsule (rather big coil, so difficult to control the beam). Both types work on the mains voltage, so the output in terms of lm/w will be similar. PAR20 will be more used in professional applications where the MR16 with GU10 made the biggest inroad in the home lighting.
Their connector is different. PAR20 is a screw base, just as its name, with screw thread around its base. You can have a look the screw base like this, http://www.alled.com.au/goods-242-6X240V+7W+LED+E27+Downlight+Globe+Free+Shipping.html
While the GU10 connector, there are double bi-pin at the bottom. See the picture to have a look.
Indeed GU10 is a base, it's the twist-and-lock that is reserved for mains-voltage lamps, typically producing a beam of light.
PAR20 is strictly speaking a names that refers to the reflector shape of the lamp (it is parabolic) however as Alex and Ben correctly point out, it normally comes with an edison screw base.
Please note that GU10 lamps exist as tungsten and LED, and that PAR20 lamps exist as tungsten, metal halide and LED.
The PAR20 is noticeably larger than the GU10.