sitelights
07-22-2003, 06:27 PM
Why are there so many lamp base and socket types in low voltage applications? To prevent, as much as possible, overlamping the luminaire and creating a fire hazard; "overlamping" is simply placing a higher watt lamp into a fixture and exceeding its rating. Conversely "underlamping" is using a lamp that is below the rating of the luminaire. Ideally it would be physically impossible to use the wrong i.e. higher watt lamp; in practice there are a number of circumstances where a luminaire can be overlamped either by accident or by design. The primary barrier to overlamping is pin spacing and pin jaw size. Bear with me while I sketch in some background. Note that nomenclature is not always jargon but lamp language is rather specialized so a halogen lamp catalog with complete specs and the appropriate photometric diagrams would be helpful.
Some years ago I was frustrated while attempting to lamp a incandescent 120v recessed light housing with a PAR lamp; I was trying to replace a 60w A19 with a 50PAR30/CAP/NSP9. I was actually going to drop below the rating of the housing but a flange in the housing prevented me from installing the PAR lamp. I also noticed that the flange did not permit the use of a larger, higher watt A21. The flange built into the housing prevented overlamping for reasons of safety. I later learned that the 50PAR30LN/CAP/SPLNSP9 would have worked since the LN (long neck) would clear the flange. Sockets sized to accept only a certain type base also provide a measure of safety; candelabra, medium and mogul bases are among the many examples.
In low voltage lighting there are similar constraints to lamping but the limiting factor is in most cases the socket not the lamp. Most 12v halogen lamps have either a bi-pin, wedge, or screw terminal base. The are some others but they are rare in landscape lighting i.e. DC Bayonet (for AR70s) or G53 (AR111s) and the SCB halogen hybrids found mostly in Focus' "all halogen" line. This lamp is a bi-pin attached to a single contact bayonet base so it can be used in place of an automotive 93, 1141, 1156 etc. There are similar 50w lamps (retrofit back-up lights) with the SCB base so it is possible but unlikely that 50w version would be used. Focus provides a lamp available only through them so at relamping time these sockets accomodate the non-halogen automotive SCBs. Some years back I had a company make an SCB base/bi-pin socket adaptor for me; they cost about $5.00 each in lots of 200. These adaptors allowed me to convert SCB luminaires to halogen but I found over the course of a few years that the added point of contact (bi-pin jaws and SCB) created another problem.
Bi-pin sockets have different pin spacing and pin jaw size that allow lower watt lamps in higher watt sockets but not vice versa.
The limiting factor in wedge base lamps is the size of the twin jaw socket and again one can go lower but not higher. Of course the contact points are not optimized when underlamping in a slightly larger socket but the lamp will light. The soft wire lamp "pins" on a wedge base lamp form a flat loop and provide four rather than two points of contact within the socket.
Screw terminal quartz-halogen lamps have such a narrow range that only seven in 50w and below are available:36PAR36/CAP/VNSP9, /NSP13 and /WFL32 that is in 9, 13 and 32 degree beams; a 50PAR36/CAP/VNSP6, /NSP13, /WFL32 and the recent addition of a 25PAR36/CAP 12v lamp. A non-halogen "signal" lamp, the 4414 is also available in 14w; and two other non-halogen PAR lamps in 18w and 36w. Contrast this with the fourteen available MR-16 lamps in 50w or less. The size of the PAR lamp luminaire becomes obtrusive in a garden setting and this is why they are found primarily in in-ground applications.
Bi-pin sockets accept MR-16 lamps in the range of 10 to 75 watts because the pin spacing and the jaws that accept the pins are all the same: GU5.3, that is 5.3mm between the pins. MR-11s and MR8s are all GU4 at 4mm between the pins. These MR lamps are available in a complete range of beams from 8 to 60 degrees in 10, 20, 35, 42 50, 65 and 75w ratings. Never use an MR lamp that does not have a front glass bonded cover.
The GU4 socket designated G4 in bare lamp, non-MR applications will accept T3 lamps in the 10-20w range but the T4 35-75w lamp needs a GY6.35 socket. A T4 20w lamp with the GY6.35 base is also available and it is a handy item when de-rating a high watt luminaire. Usually, but not always, the 35w and up bi-pin lamps have thicker pins that will not fit into a T3 socket.
Wedge base lamps in the 3-5w range fit the smallest socket and the 8-18w range fit the larger socket but a bi-pin lamp of higher wattage can fit into this socket well enough to light up. Anything that can happen will happen.
Human folly having no bounds one could jury rig an AR111 lamp in the 35-100w range to a PAR lamp screw terminal luminaire thereby courting disaster.
The AR70 lamp should be removed from the market because the DC Bayonet base lamp will fit into a DC Bayonet socket that is designed to handle only up to about 25w but the AR70 will fit and is available in 50w to cook the luminaire.
Any fool can overlamp an MR16 luminaire by simply not heeding the manufacturer's MAX label; most if not all MR16 spotlights are rated for 50w. New mandatory test procedures promulgated by UL have forced manufacturers to redesign their spotlights. Notoriously, the superceded Hadco BL616, despite all my letters and emails about the misleading label, continues to state "50w ONLY" when "50w MAX" is correct; this spotlight will soon be de-rated to 35w or dropped from the line. I've been assured that a 50w rating is crucial to holding a place in the market. The result of this cloning is that all the newer 50w rated spotlights are appreciably larger.
The problem of overlamping MR16 luminaires will persist in spite of the inherent danger of using a socket that will accept up to a 75w lamp. Everyone knows this but does nothing about it. Only the largest luminaires can handle 75w; it would be wise to change the pin spacing on the 75w MR16 so that it cannot fit into a GU5.3 socket. Osram-Sylvania limits their MR16s to 65w maximum but that should have a different base too. As is standard in the T3 and T4 bi-pin size and spacing I suggest separating the the MR socket pin size into two types: 10-20w, 35-50w and have a separate spacing dimension for the 65-75w.
As stated in other posts on this topic, there are no, zero, zilch, nada lamps made for the low voltage outdoor lighting market. None of the lamps mentioned in this post were designed or manufactured for outdoor use within 3 feet of the ground. Yo! let's at least plate the pins.
The major fault I routinely see in landscape lighting installations is high surface brightness which inhibits the ability to perceive form and texture by diminishing the eye's night vision sensitivity. I attribute this error to the probable lack of intention; intentional lighting is exactly what is wanted and what is appropriate to the setting. Unintentional lighting is either pure serendipity i.e. a happy acident or just plain lack of coherent design. High watt lamps used indiscriminately merely announce the designer's ignorance of the fundamentals of night vision accomodation and the elemental aspects of low contrast as a lighting aesthetic.
Some years ago I was frustrated while attempting to lamp a incandescent 120v recessed light housing with a PAR lamp; I was trying to replace a 60w A19 with a 50PAR30/CAP/NSP9. I was actually going to drop below the rating of the housing but a flange in the housing prevented me from installing the PAR lamp. I also noticed that the flange did not permit the use of a larger, higher watt A21. The flange built into the housing prevented overlamping for reasons of safety. I later learned that the 50PAR30LN/CAP/SPLNSP9 would have worked since the LN (long neck) would clear the flange. Sockets sized to accept only a certain type base also provide a measure of safety; candelabra, medium and mogul bases are among the many examples.
In low voltage lighting there are similar constraints to lamping but the limiting factor is in most cases the socket not the lamp. Most 12v halogen lamps have either a bi-pin, wedge, or screw terminal base. The are some others but they are rare in landscape lighting i.e. DC Bayonet (for AR70s) or G53 (AR111s) and the SCB halogen hybrids found mostly in Focus' "all halogen" line. This lamp is a bi-pin attached to a single contact bayonet base so it can be used in place of an automotive 93, 1141, 1156 etc. There are similar 50w lamps (retrofit back-up lights) with the SCB base so it is possible but unlikely that 50w version would be used. Focus provides a lamp available only through them so at relamping time these sockets accomodate the non-halogen automotive SCBs. Some years back I had a company make an SCB base/bi-pin socket adaptor for me; they cost about $5.00 each in lots of 200. These adaptors allowed me to convert SCB luminaires to halogen but I found over the course of a few years that the added point of contact (bi-pin jaws and SCB) created another problem.
Bi-pin sockets have different pin spacing and pin jaw size that allow lower watt lamps in higher watt sockets but not vice versa.
The limiting factor in wedge base lamps is the size of the twin jaw socket and again one can go lower but not higher. Of course the contact points are not optimized when underlamping in a slightly larger socket but the lamp will light. The soft wire lamp "pins" on a wedge base lamp form a flat loop and provide four rather than two points of contact within the socket.
Screw terminal quartz-halogen lamps have such a narrow range that only seven in 50w and below are available:36PAR36/CAP/VNSP9, /NSP13 and /WFL32 that is in 9, 13 and 32 degree beams; a 50PAR36/CAP/VNSP6, /NSP13, /WFL32 and the recent addition of a 25PAR36/CAP 12v lamp. A non-halogen "signal" lamp, the 4414 is also available in 14w; and two other non-halogen PAR lamps in 18w and 36w. Contrast this with the fourteen available MR-16 lamps in 50w or less. The size of the PAR lamp luminaire becomes obtrusive in a garden setting and this is why they are found primarily in in-ground applications.
Bi-pin sockets accept MR-16 lamps in the range of 10 to 75 watts because the pin spacing and the jaws that accept the pins are all the same: GU5.3, that is 5.3mm between the pins. MR-11s and MR8s are all GU4 at 4mm between the pins. These MR lamps are available in a complete range of beams from 8 to 60 degrees in 10, 20, 35, 42 50, 65 and 75w ratings. Never use an MR lamp that does not have a front glass bonded cover.
The GU4 socket designated G4 in bare lamp, non-MR applications will accept T3 lamps in the 10-20w range but the T4 35-75w lamp needs a GY6.35 socket. A T4 20w lamp with the GY6.35 base is also available and it is a handy item when de-rating a high watt luminaire. Usually, but not always, the 35w and up bi-pin lamps have thicker pins that will not fit into a T3 socket.
Wedge base lamps in the 3-5w range fit the smallest socket and the 8-18w range fit the larger socket but a bi-pin lamp of higher wattage can fit into this socket well enough to light up. Anything that can happen will happen.
Human folly having no bounds one could jury rig an AR111 lamp in the 35-100w range to a PAR lamp screw terminal luminaire thereby courting disaster.
The AR70 lamp should be removed from the market because the DC Bayonet base lamp will fit into a DC Bayonet socket that is designed to handle only up to about 25w but the AR70 will fit and is available in 50w to cook the luminaire.
Any fool can overlamp an MR16 luminaire by simply not heeding the manufacturer's MAX label; most if not all MR16 spotlights are rated for 50w. New mandatory test procedures promulgated by UL have forced manufacturers to redesign their spotlights. Notoriously, the superceded Hadco BL616, despite all my letters and emails about the misleading label, continues to state "50w ONLY" when "50w MAX" is correct; this spotlight will soon be de-rated to 35w or dropped from the line. I've been assured that a 50w rating is crucial to holding a place in the market. The result of this cloning is that all the newer 50w rated spotlights are appreciably larger.
The problem of overlamping MR16 luminaires will persist in spite of the inherent danger of using a socket that will accept up to a 75w lamp. Everyone knows this but does nothing about it. Only the largest luminaires can handle 75w; it would be wise to change the pin spacing on the 75w MR16 so that it cannot fit into a GU5.3 socket. Osram-Sylvania limits their MR16s to 65w maximum but that should have a different base too. As is standard in the T3 and T4 bi-pin size and spacing I suggest separating the the MR socket pin size into two types: 10-20w, 35-50w and have a separate spacing dimension for the 65-75w.
As stated in other posts on this topic, there are no, zero, zilch, nada lamps made for the low voltage outdoor lighting market. None of the lamps mentioned in this post were designed or manufactured for outdoor use within 3 feet of the ground. Yo! let's at least plate the pins.
The major fault I routinely see in landscape lighting installations is high surface brightness which inhibits the ability to perceive form and texture by diminishing the eye's night vision sensitivity. I attribute this error to the probable lack of intention; intentional lighting is exactly what is wanted and what is appropriate to the setting. Unintentional lighting is either pure serendipity i.e. a happy acident or just plain lack of coherent design. High watt lamps used indiscriminately merely announce the designer's ignorance of the fundamentals of night vision accomodation and the elemental aspects of low contrast as a lighting aesthetic.