240V Halogen Light Fittings

[rhamer]

Has anybody got any experiences to share about 240V Halogen lights and C-Bus dimmer units?

Does it work ok? Are there any traps? Does it effect globe life?


Regards

Rohan

[Forumadmin]

I've had no problems dimming these fittings. Not so far anyway.

[coppo1]

Feel free to correct me where required......

From a little experience with these i have not seen any real difference between 240vac halogen
and 12vdc halogen.
Any lighting experts feel free to interject here.

C-Bus dimming of Low voltage Halogen:
From a project i was involved in years ago i found the following-

A Gaming Room we did required dimming of halogens (12vdc) , due to the
amount of pokie machines in the room , the customer required the halogen
lights to be dimmed down to approx 30% level for 90% of the day.

After talking to some lighting guys i know, they informed me that when halogen lamps run at full 100% a
"re-cycling" process happens and crap given off by the filament gets burnt and returned to the filament.
( or something like that )
If it is dimmed down to a low level (30%) the burning of crap ( technical term "crap")
does not happen, thus the re-cycling process fails and the result is "black" lamps.

Their was an old minder on the job so the following was done.

Customer could hit various cbus buttons acting as preset triggers for their dimmed scenes
stored in the minder.

A daily schedule was written so that when the function room was closed
( 3AM or so) that an "ALL ON 100%" scene was run for approx 15minutes to acts as a "burn -off".
15 minutes later an "ALL OFF" scene was run to reset loads.



Seemed to work OK.

[rhamer]

I too have heard that running halogen lights at less than 100% can be an issue.

However I have dimmed the 12v type before via C-Bus and had years of life from them.

I was really asking about using them as they dont have a transformer and so would present a different sort of load to the dimmer unit.

Regards

Rohan

[coppo1]

I too have heard that running halogen lights at less than 100% can be an issue.
Rohan

There is no difference to C-Bus, they are a halogen light, that is effectively seen as the same load type as an incandescent globe. Just different burning temperature to my knowledge.

[Forumadmin]

Here's a bit of a run down on Halogen lamps and how they work. Basically its a case of you get what you pay for with Halogen lamps, the gas used and quality of manufacture.
Anyhow....

The halogen cycle, What are halogen bulbs?

A halogen bulb is an ordinary incandescent bulb, with a few modifications. The fill gas includes traces of a halogen, often but not necessarily iodine. The purpose of this halogen is to return evaporated tungsten to the filament.
As tungsten evaporates from the filament, it usually condenses on the inner surface of the bulb. The halogen is chemically reactive, and combines with this tungsten deposit on the glass to produce tungsten halides, which evaporate fairly easily. When the tungsten halide reaches the filament, the intense heat of the filament causes the halide to break down, releasing tungsten back to the filament.
This process, known as the halogen cycle, extends the life of the filament somewhat. Problems with uneven filament evaporation and uneven deposition of tungsten onto the filament by the halogen cycle do occur, which limits the ability of the halogen cycle to prolong the life of the bulb. However, the halogen cycle keeps the inner surface of the bulb clean. This lets halogen bulbs stay close to full brightness as they age.
In order for the halogen cycle to work, the bulb surface must be very hot, generally over 250 degrees Celsius (482 degrees Fahrenheit). The halogen may not adequately vaporize or fail to adequately react with condensed tungsten if the bulb is too cool. This means that the bulb must be small and made of either quartz or a high-strength, heat-resistant grade of glass known as "hard glass".
Since the bulb is small and usually fairly strong, the bulb can be filled with gas to a higher pressure than usual. This slows down the evaporation of the filament. In addition, the small size of the bulb sometimes makes it economical to use premium fill gases such as krypton or xenon instead of the cheaper argon. The higher pressure and better fill gases can extend the life of the bulb and/or permit a higher filament temperature that results in higher efficiency. Any use of premium fill gases also results in less heat being conducted from the filament by the fill gas, meaning more energy leaves the filament by radiation, meaning a slight improvement in efficiency.

Lifetime and efficiency of halogen bulbs

A halogen bulb is often 10 to 20 percent more efficient than an ordinary incandescent bulb of similar voltage, wattage, and life expectancy. Halogen bulbs may also have two to three times as long a lifetime as ordinary bulbs, sometimes also with an improvement in efficiency of up to 10 percent. How much the lifetime and efficiency are improved depends largely on whether a premium fill gas (usually krypton, sometimes xenon) or argon is used.



Halogen Bulb Failure Modes

Halogen bulbs usually fail the same way that ordinary incandescent bulbs do, usually from melting or breakage of a thin spot in an aging filament.
Thin spots can develop in the filaments of halogen bulbs, since the filaments can evaporate unevenly and the halogen cycle does not redeposit evaporated tungsten in a perfect, even manner nor always in the parts of the filament that have evaporated the most.
However, there are additional failure modes.
One failure mode is filament notching or necking. Since the ends of the filament are somewhat cool where the filament is attached to the lead wires, the halogen attacks the filament at these points. The thin spots get hotter, which stops the erosion at these points. However, parts of the filament even closer to the endpoints remain cool and suffer continued erosion. This is not so bad during continuous operation, since the thin spots do not overheat. If this process continues long enough, the thin spots can become weak enough to break from the weight of the filament.
One major problem with the "necked" ends of the filament is the fact that they heat up more rapidly than the rest of the filament when the bulb is turned on. The "necks" can overheat and melt or break during the current surge that occurs when the bulb is turned on. Using a "soft-start" device prevents overheating of the "necks", improving the bulb's ability to survive "necking". Soft-start devices will not greatly extend the life of any halogen bulbs that fail due to more normal filament "thin spots" that run excessively hot.
Some halogen bulbs may usually burn out due to filament end necking, and some others may usually burn out from thin, hot spots forming in the filament due to uneven filament evaporation/recovery. Therefore, some models may have a significantly extended life from "soft-starting" and some other models may not.
It is generally not a good idea to touch halogen bulbs, especially the more compact, hotter-running quartz ones. Organic matter and salts are not good for hot quartz. Organic matter such as grease can carbonize, leaving a dark spot that absorbs radiation from the filament and becomes excessively hot. Salts and alkaline materials (such as ash) can sometimes "leach" into hot quartz, which typically weakens the quartz, since alkali and alkaline earth metal ions are slightly mobile in hot glasses and hot quartz. Contaminants may also cause hot quartz to crystalize, weakening it. Any of these mechanisms can cause the bulb to crack or even violently shatter. If a quartz halogen bulb is touched, it should be cleaned with alcohol to remove any traces of grease. Traces of salt will also be removed if the alcohol has some water in it.
Since the hotter-running quartz halogen bulbs could possibly violently shatter, they should only be operated in suitable fully enclosed fixtures.



Use of Halogen Bulbs with Dimmers

Dimming a halogen bulb, like dimming any other incandescent lamp, greatly slows down the formation of thin spots in the filament due to uneven filament evaporation. However, "necking" or "notching" of the ends of the filament remains a problem. If you dim halogen lamps, you may need "soft-start" devices in order to achieve a major increase in bulb life.
Another problem with dimming of halogen lamps is the fact that the halogen cycle works best with the bulb and filament at or near specific optimum temperatures. If the bulb is dimmed, the halogen may fail to "clean" the inner surface of the bulb. Or, tungsten halide that results may fail to return tungsten to the filament. Halogen bulbs have sometimes been known to do strange and scary things when greatly dimmed.
Halogen bulbs should work normally at voltages as low as 90 percent of what they were designed for. If the bulb is in an enclosure that conserves heat and a "soft-start" device is used, it will probably work well at even lower voltages, such as 80 percent or possibly 70 percent of its rated voltage. However, do not expect a major life extension unless soft-starting is used. Even with soft-starting, do not expect to more than double or possibly triple the life of any halogen bulb already rated to last 2,000 hours or more. Even with soft starting, the life of these bulbs will probably not continue to improve much as voltage is reduced to less than about 90 percent of the bulb's voltage rating.

Dimmers can be used as soft-start devices to extend the life of any particular halogen bulbs that usually fail from "necking" of the ends of the filament. The bulb can be warmed up over a period of a couple of seconds to avoid overheating of the "necked" parts of the filament due to the current surge that occurs if full voltage is applied to a cold filament. Once the bulb survives starting, it is operated at full power or whatever power level optimizes the halogen cycle (usually near full power)
The dimmer may be both "soft-starting" the bulb and operating it at slightly reduced power, a combination that often improves the life of halogen bulbs. Many dimmers cause some reduction in power to the bulb even when they are set to maximum.
(A suggestion from someone who starts expensive medical lamps by turning up a dimmer and reports major success in extending the life of expensive special bulbs from doing this as Coppo suggested.) Running the lamp flat out for a few mins will extend its lifecycle.

[coppo1]

I inquired at a Delights store the other day for 240 Dichroics as opposed to
the 12volt versions.

The salesperson advised not to got the 240V and to stick with the 12 v
because the lamp-life of the 240v version is not as good.

Mind you she also quoted that they use G-E preciseline, which to my previous experience
is considered a very good quality lamp. Considering the quantities those
guys must sell, they should have a good idea.

Any experiences with poorer lamp life from 240V dichroics??