MR16 and MR11,Multifaceted reflector

Multifaceted reflector
MR16 and MR11 (sometimes referred to as MR-16 or MR-11, rarely MR8 or MR-8) are standard formats for halogen multifaceted reflector light bulbs made by a variety of manufacturers. MR16-compatible LED lamps are also available. MR16 lamps are regularly used in place of standard incandescent light bulbs for applications including residential lighting and retail lighting, while MR11 ones are used in specialty applications. MR16 lamps were originally designed for use in slide projectors. They are well suited to a variety of applications that require directional lighting of low to medium intensity, such as track lighting, recessed ceiling lights (only if not dichroic), desk lamps, pendant fixtures, landscape lighting, retail display lighting and bicycle headlights

Left to right: MR16 with GU10 base and with GX5.3 base, MR11 with GU4 or GZ4 base

Designation

MR16 is a coded designation in which MR stands for multifaceted reflector, and 16 is the number of eighths of an inch the front is in diameter. An MR16 is 2 inches (51 mm), an MR11 is 1.375 inches (35 mm).

[edit] Halogen MR16 characteristics

[edit] Design and construction

Halogen MR16 lamps consist of a halogen capsule (bulb) integrated with a pressed glass reflector. The reflector of an MR16 lamp is 2 inches (50mm) in diameter. The base conforms to bi-pin GU5.3 standard. The compact size of the MR16 allows for much smaller, more discreet fixtures than the incandescent reflector bulbs that pre-dated MR16s.

The reflector controls the direction and spread of light cast from the lamp. MR16 lamps are available with different beam angles from narrow spot lights of as small as 7 degrees to wide flood lamps of 60 degrees.

"MR" refers to multifaceted reflector, indicating that this reflector is usually shaped with multiple small facets. This multifaceted reflector gives a soft edge to the area illuminated by the lamp. MR16 lamps are also available with smooth reflectors, resulting in a sharper fall-off to the illuminated area. "16" refers to the maximum diameter of the lamp in eighths of an inch, 16/8" or 2 inches (5 cm).

[edit] Dichroic reflectors

In less-expensive lamps, the reflector has an aluminium coating that reflects all light. In more-expensive lamps, the reflector commonly has a dichroic coating that reflects particular frequencies of the visible spectrum in the direction the lamp is facing, while not reflecting infrared light. By not reflecting infrared light (which produces heat), these lamps reduce the amount of heating of the subject upon which they are focused. The combination of the halogen light source and dichroic coating also means that these lamps provide a high color rendering index and a higher color temperature than standard incandescent bulbs. This makes them well suited to applications where color rendering is important, such as retail display lighting.

Dichroic lamps, however must never be used in recessed lighting as they are a common ignition source for building fires.^{[citation needed]} In some countries (e.g. UK, Australia), lamps suitable for use in recessed lighting can be identified by the IEC 60598 No Cool Beam symbol.

[edit] Operation

The brightness of MR16 lamps can be adjusted when used with appropriate light fixtures and dimmers. However, the color temperature changes significantly when the lamp is dimmed.

MR16 lamps produce significant heat, and care must be taken to avoid contact with skin or proximity to flammable materials when the lamp is on or has been on recently.

Halogen MR16 lamps are typically more efficient than standard incandescent bulbs, but not nearly as efficient as fluorescent lamps or LED technology. MR16 lamps typically have a life expectancy of 1000 to 3000 hours.

With both types of incandescent bulbs, useful life can be considerably shortened if their filaments experience mechanical shock or vibration. Using an electronic transformer with a 'soft start' feature can considerably extend life as it reduces the characteristically high inrush current which occurs shortly after switch-on. Additionally, it can be less strainful on the eyes, giving the pupils more time to react to a sudden increase in environmental lighting level.

MR16 lamps, like all quartz-halogen lamps, produce substantial amounts of ultraviolet light. Usually, this must be filtered out. Also, the quartz capsule of the lamp sometimes ruptures ("explodes") upon failure of the lamp. For these two reasons, some MR16 lamps include a cover glass that serves as an integrated ultraviolet filter and explosion shield. MR16 lamps lacking this cover require the use of a fixture that incorporates an external piece of glass specifically designed to provide this protection.

[edit] Compatible LED replacements

 

LED MR11, 70 lm/W LED MR16

MR16-compatible LED lamps are also available. They are similar in shape to halogen MR16 lamps, and can be used in most fixtures designed for MR16 lamps. The same is true of MR11-compatible LED lamps.

Versions of the led lamps have been patented in the UK^{[citation needed]}. Due to the low heat and power consumption, they have been produced from plastic, although this does not affect their efficiency. Their non-polarised AC/DC operation, with current limitation over a wide voltage range (11.5 ~ 18 volts as a standard 12 volt version), allows a wide range of usage.

Average rated life, as quoted by manufacturers, is typically 30,000–50,000 hours depending on the product in question. This amounts to continuous operation for 1250–2080 days or approximately 24 hours per day, for three to six years.

Fixtures designed for halogen MR16 or MR11 lamps that use electronic transformers may need to be retrofitted with LED-compatible transformers. This is because the standard electronic transformers have a minimum power-usage requirement in order to function. Some LED-lamps may be below this usage requirement. Fixtures that use magnetic transformers can generally be used with LED-lamps without modification.

LED-lamps from some manufacturers incorporate full wave rectification circuitry into the 'bulb', so that either AC or DC can be used, whilst others require a DC supply and correct polarity.

At this time, there are few standards for MR16 and MR11 compatible LED lamps. As such there is a wide variety of designs, varying significantly with regard to beam width, light colour, efficiency and luminous power.

Unlike halogen MR16s, LED-lamps often do not have the multifaceted reflectors that give MR16s their precise beam width control. Some rely on the optics of the LED(s) to control the beam width. Some designs may have simple cut-off apertures that limit beam width, or even individual reflectors for each LED.

As with other LED lamps available today, the quality and color temperature of the white light produced by such lamps varies. Many tend towards the blue end of the spectrum, being even "cooler"-coloured than fluorescent lighting. Because of this variability, some MR16 and MR11 compatible LED lamps will create significantly more natural looking light than others.

The least efficient of these lamps produce about 26 lumens per watt (lm/W), which is similar to the efficiency of halogen MR16s. The most efficient of these lamps available today produce about 100 lm/W, which exceeds the efficiency of compact fluorescent lamps.

In terms of total luminous power, such lamps range from being significantly less powerful than their halogen counterparts, to being comparable to the lower power halogen MR16s. The brightest available halogen MR16s are still slightly brighter than the brightest available LED versions.

[edit] Variations

MR16 lamps most often operate at 12 volts, although they are also available in other voltages. The common 12-volt MR16 lamps therefore require a magnetic or electronic transformer (sometimes misnamed as a ballast) to convert the 120 or 240 volt mains voltage to the very low operating voltage required by the lamp. Note that although halogen MR16 lamps can usually operate on either AC or DC voltage, LED devices require DC voltage and as such will require a rectifier in the unit if AC is to be used.

Certain MR16 lamps can operate directly on the mains voltage. These lamps typically use a GU10 turn-and-lock base, so they cannot be accidentally interchanged with low-voltage lamps. As such, they are often referred to as GU10 rather than MR16 lamps. Because of their use of much-finer wire, the filaments of lamps that operate directly from mains voltage are much more fragile than those used in low-voltage lamps.

Low-voltage MR16 lamps almost always have ANSI standard GU5.3 two-pin bases. MR16 lamps with an integrated transformer are also available. These lamps have screw bases to fit standard medium-base Edison sockets.

Smaller lamps are also manufactured in the less common MR11 and even less common MR8 formats, which have reflectors that are 1⅜ inch (11/8" or 35 mm) and 1 inch (8/8" or 25 mm) in diameter, respectively. These smaller lamps appear very similar to MR16 lamps, also featuring similar multifaceted reflectors that are available in a variety of beam spreads. Their smaller size makes possible even smaller fixtures, but limits them to lower powers. MR11 and MR8 lamps have pins placed more closely together, preventing them from accidentally being interchanged with MR16 lamps.

Feit Electric produces a compact fluorescent version that can replace an MR16, however this runs only a few watts, and scatters the small amount of light widely, thus is only suitable for limited applications.