Garden Lighting Help sheet  No. 5: - Halogen lamp choice

12 volt MR16 reflector lamps

50mm in diameter and fit most low voltage outdoor spotlights, recessed uplights, downlights, recessed steplights and underwater lights except miniature garden lighting fittings such as the M2600 Piccolo planter light and copper hanging downlights M6450/M6455/M6460 which are stated as using the smaller MR11 lamp. Claimed average lamp life is 3000-4000 hours, which should be halved for outside use; 1000 hours is about the same as having your garden lighting on every night of the year for about 3 hours. Choosing lamps (bulbs) for any type of exterior spotlight, uplight, or downlight which uses a low voltage MR16 halogen spotlight lamp is partly a question of brightness and partly one of correct beam angle.

Beam angle

The principal beam angles are 12, 24, 36 and 60 degrees. Sometimes you will want a small pool of light from a narrow beam to accent a feature without lighting the surroundings; other garden lighting subjects, such as lighting diagonally across shrub borders, will require the widest coverage available, such as a 60⁰ beam. For example, a 60⁰ beam will provide wide coverage from a pergola beam only 1.5 metres above a table below, but if you are uplighting a slender tree the coverage of a 60⁰ beam will be wasted in the night sky; a narrower beam will “fit” the shape of the tree more closely.

Brightness

Brightness isn’t just about the wattage of the lamp. The brightness of a 20 watt lamp squeezed into a narrow spot beam can produce a brighter pool of light than that of a 50 watt lamp projected in a wide flood beam. So, first “fit” the beam angle to your subject, then think about brightness.

MR11 reflector lamps

35mm in diameter and fit the Megabay M2600 Piccolo planter light and copper hanging downlights M6450/M6455/M6460, as well as the Elipta Microspot and other miniature garden lighting fittings. These garden light fittings will accept a 35 watt lamp but we recommend a 20 watt lamp for most applications to reduce heat in the fitting and prolong lamp life. The MR11 lamp is also the coolest 20w halogen lamp option for the Nautilus recessed uplight. 

Halogen capsule lamps

Used in Megabay spreadlights, the M2099 light for use in oriental stone lanterns and other objects, and a variety of recessed & surface mount steplights. 20 watt lamps are normally used in most of these fittings and have the smaller G4 pins, same as the optional 10 watt lamp. Megabay copper spreadlights (M6405/M6410/M6415/M6420/M6425) can be fitted with 35 watt or 50 watt GY6.35 lamps for applications requiring exceptional brightness. Claimed average lamp life is 1000-2000 hours. 

240 volt GU10 reflector lamps

Similar in size and frontal appearance to 50mm MR16 lamps; they offer the advantages of 240v operation for ease of wiring, on house walls for example, and the use of a compact exterior light fitting which doesn’t need to house a bulky transformer. These usually outweigh the disadvantages; they are less efficient than MR16 lamps, meaning the light output per watt is less, and they have a shorter life of 2500-4000 hours. The choice of lamp wattage and beam angles is less than with MR16 12 volt fittings but is adequate for most general purpose downlighting, uplighting and accent lighting applications in the garden. GU10 lamps are used in Elipta’s 240v exterior spotlights and some BEL recessed halogen uplights.

NB. See also Help sheet 6 - Choosing lamps for spotlights