Multifaceted reflector

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Left to right: MR16 with GU10 base, MR16 with GU5.3 base, MR11 with GU4 or GZ4 base

A multifaceted reflector (MR) light bulb is a format for halogen bulbs, made by a variety of manufacturers. MR lamps were originally designed for use in slide projectors, but are now used in applications including residential lighting and retail lighting. They are suited to a variety of applications that require directional lighting, such as track lighting, recessed ceiling lights, desk lamps, pendant fixtures, landscape lighting, retail display lighting and bicycle headlights. Lamps are designated by symbols such as "MR 16" where the diameter is represented by numerals. Common sizes for general lighting are MR 16 and MR 11, with MR 20 and MR 8 used in specialty applications.

Compact fluorescent lamps and LED lamps interchangeable with some sizes of MR halogen lamps are now available.

Designation

MR16 is a coded designation in which MR stands for multifaceted reflector, and 16 is the diameter in eighths of an inch across the front face. An MR16 is sixteen eighths, or 2 inches (51 mm) in diameter and an MR11 is 11 eighths, or 1.375 inches (34.9 mm) in diameter.

A common derivative is known as GU10, referring to the lamp cap fitting format invented by Havells Sylvania in 1997,[1] distinguishable from other MR lamps by the 'U' shaped ceramic base mount with 10mm (pin center to center distance) 2-pin bayonet-style twist lock, and by being mains voltage.

History

The MR16 lamp was first sold in 1965. Emmett H. Wiley of General Electric (USA) was awarded patent #3,314,331 for a miniature reflector lamp in 1967. The innovation was using the lamp rim, rather than the base, as the reference plane for focusing. This allowed more flexible electrical mounting arrangements and more precise focussing.[2] Note that this lamp was not "multifaceted"; faceted reflectors were introduced in 1971.

Halogen MR16 characteristics

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 (51 mm) 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° to wide flood lamps of 60°.

"MR" refers to the multifaceted reflector which has multiple small facets. This 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.

Dichroic reflectors

Some lamps use an aluminum coating as a reflector. Others use selective dichroic coating that reflects visible light and allows infrared radiation to pass through. This type reduces heating of illuminated objects since less infrared radiation is present in the light beam. However, dichroic lamps must only be used in compatible fixtures that can dissipate the heat.[3] Dichroic lamps must not be fitted to recessed or enclosed luminaires with the IEC 60598 No Cool Beam symbol.[4]

IEC 60598 No Cool Beam symbol

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.

Low voltage halogen lamps, such as MR16 lamps often have a better efficacy than line voltage incandescent lamps but not nearly as efficient as gas discharge lamps or some LED lamps.

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 that occurs initially when the lamp is cold. Dimming also extends life significantly.

MR16 lamps, like all quartz-halogen lamps, produce some ultraviolet light. Usually, this must be filtered out. Also, the quartz capsules of the lamps may rupture or explode upon failure of the lamps. 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 both ultraviolet and physical protection.

MR16 lamps are available in 10–50 W power ratings (150–800 lumens).[5]

Alternatives

See also: LED lamp
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. Fixtures designed for halogen MR16 or MR11 lamps that use electronic transformers may need to be retrofitted with LED-compatible transformers. 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.[citation needed]

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

MR16-compatible compact fluorescent lamps are also available. As of 2012 they tend to be cheaper than LED replacements and have comparable efficiency, but they may not be available with high output or with narrow flood angles.

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 ferromagnetic or electronic transformer—sometimes misnamed as a ballast—to convert the 120- or 230-volt mains voltage to the very low operating voltage required by the lamp. MR16 lamps may also be operated from direct current, but will have a shortened life.[citation needed]

Although halogen incandescent MR16 lamps usually operate on AC voltage, LED devices require direct current and require a rectifier and current driver in the unit. The current driver is commonly a buck–boost converter or buck converter. The rectifier must be able to operate efficiently at the high frequencies produced by electronic transformers and should also incorporate safety devices that operate in the event of component failure.[6]

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. They are often referred to as GU10, rather than MR16 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 closer together, preventing them from accidentally being interchanged with MR16 lamps.

MR16 lamps are commonly available in range of color temperatures, from about 2700 K to 7000 K, to satisfy various applications.

Advantages

MR16 lamps offer several advantages over other lamps with equivalent power ratings. They are typically smaller (transformers excepted), provide better beam control and offer a whiter light than ordinary incandescent lamps. The small size of the lamp allows designers more flexibility in placing the lamps and with the option of various beam widths, the light beam can be very specifically placed.

White LED MR16 lamps can be manufactured with different colour temperatures, normally ranging from warm whites, attempting to match the colour of halogens, all the way through to cool whites at 5500 K or more.

Disadvantages

MR16 lamps have several disadvantages over other types of lighting, most notably their high operating temperature and pressurized bulb. The halogen bulb can reach temperatures over 200°C,[citation needed] increasing the risk of fire should anything flammable come in contact or even be in close proximity to the bulb or fixture. The quartz capsule containing the filament and halogen gas is pressurized and can explode if improperly handled or damaged, and must be handled carefully prior to installation to prevent contamination with oil and salt from fingerprints, which can dramatically shorten the lamp's life.[citation needed]

Mounted clear of roof insulation and with an inbuilt air space around the luminaire fitting, they effectively form small chimneys resulting in heat lost from the room space to the roof space.[7]

In dusty environments, the high temperatures produced contribute to a burnt smell.[citation needed]

ANSI designations

A typical MR16 lamp

The following ANSI standard codes are used to designate certain power and beam angle combinations for MR16 lamps. Many manufacturers use these standard codes for lamps matching these specifications:

  • ESX: 20 watt, 10 degree beam (20MR16/10°)
  • BAB: 20 watt, 35 degree beam (20MR16/35°)
  • EXT: 50 watt, 15 degree beam (50MR16/15°)
  • EXZ: 50 watt, 25 degree beam (50MR16/25°)
  • EXN: 50 watt, 40 degree beam (50MR16/40°)
  • FNV: 50 watt, 60 degree beam (50MR16/60°)
  • FPA: 65 watt, 15 degree beam (65MR16/15°)
  • FPC: 65 watt, 25 degree beam (65MR16/25°)
  • FPB: 65 watt, 40 degree beam (65MR16/40°)
  • EYF: 75 watt, 15 degree beam (75MR16/15°)
  • EYJ: 75 watt, 25 degree beam (75MR16/25°)
  • EYC: 75 watt, 40 degree beam (75MR16/40°)

Note that MR16 lamps are available in many other power and beam combinations than those available above. For this reason, MR16 lamps are also often labeled according to beam spread abbreviations. Note that these while these abbreviations are commonly used, the angles associated with these abbreviations vary slightly from manufacturer to manufacturer. Typical beam angles for these beam spread abbreviations are as follows:

  • VNSP (very narrow spot): less than 8 degrees
  • NSP (narrow spot): 8-15 degrees
  • SP (spot): 8-20 degrees
  • NFL (narrow flood): 24-30 degrees
  • FL (flood): 35-40 degrees
  • WFL (wide flood): 55-60 degrees
  • VWFL (very wide flood): 60 degrees or more

See also

References

  1. ↑ "Direct LED Replacement Launched". Sylvania press release. Retrieved 28 February 2012. 
  2. ↑ http://www.lamptech.co.uk/Spec%20Sheets/TH%20RM%20Q150MR16-21%20EJM%20GE.htm
  3. ↑ Incidents – Cheshire Fire and Rescue Service
  4. ↑ Downlighters and fire safety – Electrical Safety Council
  5. ↑ "Replace Inefficient MR16 Halogen Lamps with LEDs". Maxim. September 25, 2007. 
  6. ↑ , MAXIM: LED driver solution for MR16 and similar retrofit lamps
  7. ↑ , BB0502: Air Leakage in Recessed Lights

External links

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