Best retro purpose
Metal Hallide lamps are still widely used on commercial, industrial and architectural lighting but in these applications LED lamps are quickly replacing them due to much better performance, lower energy consumption and easy servicing. Light appearance is coll white or daylight, depending on lamp model, with good colour reproduction and low ultraviolet emission. The lamp can be used indoors as well as outdoors, when intense lighting is required as most surrounding look quite pleasing being light with new lamps. With the most common gear, an electromagnetic ballast along with an ignitor, flicker is noticeable.
With adequate care and good ventilation, HQI-T metal hallides can be used vertically, in a freestanding position as mercury vapour lamps but lifetime will be reduced. HQI-T lamps of lower wattages are slightly more sensitive to operating position than higher wattage ones. Lamps age differently and this means that a series of lamps may exhibit different colour intensity and light intensity depending on wear and group replacement should be considered to maintain uniformity. Just as well, lamps should be replaced as soon as light and colour uniformity is affected, as old lamps present a higher risk of catastrophic failure.
Overall, this range of lamps is moderately successful for retro purposes as the lamps are quite efficient and have a great variety of wattages and colour designations. Colour rendering is also very good, but only for certain lamps and wattage ratings, so careful analysis of datasheets is recommended before purchase and installation. Fixtures must be designed to house this type of lamp, meaning that a lone lamp is not a good choice and a complete system must be found especially in the case of lower powered lamps that use the bi-pin base as they are specialist items.
Understanding manufacturer data
Lamp light output is always measured in lumens. This is a way of measuring by averaging light output at a distance of 1 meter in an integrating sphere. This was carried out in lab environments and this information was mentioned in lamp datasheets and catalogues. While this information is accurate it should be considered only across similar lamp types.
Lamp life is presented in thousands of hours. It does not point at a specific moment when an installed lamp will not operate anymore but a statistical point at which some of the lamps may not operate, giving a rough estimate of useful life.
Ra8 colour rendering index, or simply colour rendering index is a way of expressing the typical colour rendering capability of a lamp. While it may be non-intuitive this is a computed average of brightness of certain coloured samples that are light by the lamp. The brighter they are, the more efficient is the lamp in this task. Most lamps do not have a continuous colour spectra so only some specific colours might look very bright and others look very dull. Colour samples are not intense reds, greens and blues but intermediately vivid colours that are focused on human skin colours and some fabrics or surfaces, meaning that a only very high colour rendering indexes are desirable for indoor home lighting. Sun light renders colours almost perfectly, having a value of 100 while typical lamps have a rendering index between 50 and 80, a good value being above 80 and a poor one below 50.
Colour temperature is another important detail. The value is presented in Kelvins and follows a theory that boils down to the fact that light can be produced by heating a metal up to a specific temperature. A camp fire releases light as the flame reaches around 1500-2000 degrees Celsius and a slightly higher value expressed in Kelvin. The designation is warm white for a value of around 2700 Kelvin, natural white with a value of around 3200-3500 Kelvin, cool white for a value of around 4000-4500 Kelvin, daylight for a value between 5000 and 5500 Kelvin, and cool daylight for a value above 6000-6500 Kelvin. There are cultural preferences that make some warm colour temperatures preferred in colder climates and cool colour temperatures in warmer climates. The most popular home lighting worldwide is mostly warm white, due to a comfortable, pleasant atmosphere that is close to the old incandescent lamp.
|Designation||Base||Lamp wattage||Luminous flux||Colour appearance||Colour Temperature||Colour Rendering Index (Ra8)||Life (to 50% failures)|
|HQI-T 70W WDL (730)||G12||70 W||5300 lm||Warm White||3000 K||71||12000 hours|
|HQI-T 70W NDL (842)||G12||70 W||5800 lm||Cool White||4200 K||77||12000 hours|
|HQI-T 150W WDL (730)||G12||150 W||13000 lm||Warm White||3000 K||87||12000 hours|
|HQI-T 150W NDL (842)||G12||150 W||13000 lm||Cool White||4200 K||87||12000 hours|
|HQI-T 250W D (952)||E40||250 W||20000 lm||Daylight||5200 K||90||12000 hours|
|HQI-T 400W N (935) NAV-VG||E40||400 W||42000 lm||Neutral White||3500 K||65||12000 hours|
|HQI-T 400W N (940) HQI-VG||E40||400 W||34000 lm||Cool White||4000 K||60||12000 hours|
|HQI-BT 400W D (952) NAV-VG||E40||400 W||35000 lm||Daylight||5200 K||90||12000 hours|
|HQI-BT 400W D (959) HQI-VG||E40||400 W||27000 lm||Daylight||5900 K||90||12000 hours|
|HQI-T 1000W N (935)||E40||1000 W||110000 lm||Neutral White||3500 K||65||9000 hours|
|HQI-T 1000W D (972)||E40||1000 W||85000 lm||Cool Daylight||7250 K||90||9000 hours|
|HQI-T 2000W N (644) 230V||E40||2000 W||190000 lm||Cool White||4400 K||65||9000 hours|
- The "RX7s" base is the most popular connector for this lamp type while "FC2" is a specialist item;
- The "RX7s-24" base uses the same end connectors but spaced further apart, for higher power rated lamps;
- The "BT" designation indicates a blown-tubular or slightly higher diameter area near the arc tube;
- NAV-VG indicates that the lamp is designed for high pressure sodium vapour lamp gear;
- HQI-VG indicates that the lamp is designed for metal hallide lamp gear; lower lumen output due to lower lamp current;
- There are some 400V 2000W lamps designed for three-phase mains voltage, they are omitted due to gear and lamp rarity;
Durability and Repair-ability
Generally, metal hallide lamps fare quite poorly in terms of reliability. The aggressiveness of metal hallides and their reliance on a specific pressure and temperature requirement for vaporization and light output with a specific output, means that lamp to lamp colour shifts are quite noticeable. Aging amplifies the colour drift and light output differences. As the lamp is very compact and has high temperature hot-spots means that fixtures are noticeably degraded and especially affects gaskets and the front frame of the reflector housing. This means that waterproofing is frequently degraded and lamps are rarely suited to operate outdoors unless old fixtures are carefully maintained.
Due to the lamp being compact as well as frequent indoor applications heat degradation of the lamp gear is quite common and some design constraints may limit replacement of some ballasts and ignitors without modifying mounting points. Electromagnetic and electronic gears have been available during manufacturing but electromagnetic ballasts and ignitors were the most common ones due to lower cost. This means that special care should be taken for proper insulation and wiring and that the lamp life is slightly reduced.
Greatest features & flaws
|High light output in very compact package||Hot operating fixtures, maintenance intensive|
|High efficiency, very good colour rendering||Relatively low lamp service life|
|Directional light||Sensitive to operating position and unbalanced wearing|
|Quick lamp start||Slow restart, requires bulky, heavy, complex lamp gear|
These metal hallide lamps are well suited for indoor lighting due to their moderately high power rating and good colour reproduction. Although outdoor lighting is entirely possible, especially for higher power rated lamps. Large wattage fixtures were very popular especially for flood lighting with boxy, asymmetric or symmetric lighting patterns. The most popular power ratings were 250 and 400 Watss. The lamp itself fares well in terms of light output but the point light source nature of the lamp relegates it to accent or directional rather than general lighting.
Exterior lighting is a good application as most gardens and outside areas are well showcased. The lamps themselves do release some heat meaning that closed fixtures are not well suited if not specifically built for this purpose. Care should be taken when using these metal-hallide lamps as they are sensitive to the operating position especially when inside enclosed fixtures. Compact, boxy symmetric and asymmetric fixtures were popular. Improper heating of lamp can destroy it prematurely and present a safety hazard so special precaution should be exercised. Even if lamp warm up time is low, achieving high output quite quickly, they are slow to restart, 10 minutes pauses not being uncommon.
The lamp's performance is improved compared with typical metal hallide lamps, since very high colour rendering is available on some lamps. Unfortunately, the datasheet is highly convoluted as lamps with different bases, colour renderings and white appearance are present in the same product range. Lamps that have a daylight colour appearance have very high colour rendering index for a quartz metal hallide lamps but they suffer the same lumen output degradation as cool white lamps. Overall, cool white and daylight colour appearance lamps have the best light output stability during service life. Of course, compared with ceramic metal hallide lamps, HQI lamps are faring slightly better than average but they are still lower performing than ceramic lamps.
These lamps are somewhat better suited for frequent switching but starting is still a major stress. They need less than two minutes to reach maximum light output and less than that to restart after being turned off. The light colour and output changes from start-up to normal operation from white to orange. White light at startup and then greenish light midway to warm-up suggests mercury is also used on the lamp. This slightly improves colour rendering but affects slightly reduces lamp life while the ones that do no change colour are either new or do not use mercury at all have a yellower light appearance. Lamps without mercury are more difficult to start but they have longer lifetimes and slightly higher efficiency.
The lamp requires a conventional or electro-magnetic gear of the same power output as the lamp, connected in series with a lamp and an ignitor that must be connected as is required in the circuit. Connecting the lamp directly to mains damages it instantly as there is no current limitation. Improper connection of the ignitor is also dangerous and proper care must be exerted during installation and servicing. A power factor capacitor that has a specific value might be used to correct the power factor and current requirements on the circuit. The lamp itself is not influenced by the presence or absence of this capacitor. When used sparingly in homes or some premises where not a lot of these lamps are located, power factor correction is not important but large industrial or commercial clients were required to maintain a specific power factor due to electricity distribution contracting.
HQI-TS lamps are a good choice for directional lamp fixtures. If a fixture in good enough condition is found, the lamp offers good light output that could make it useful on interior as well as exterior applications. The most popular lamp wattage seems to be the 70W type, as it was powerful and compact enough to justify the purchase of a fixture that has an elliptical light beam. Garden lighting is not the best application choice as the lamps are not as suited as the 250W and 400W types offer much higher outputs. Indoor lighting is also limited since use in living rooms is not entirely attractive as flicker is present with conventional lamp gears and the lack of hot or quick restart and average lamp performance does not justify the much costlier electronic lamp gear.
These type of lamps were used for lighting exterior areas especially in the case of higher powered lamps while the most frequent application of low powered ones was indoor accent lighting. The lamp was relatively affordable (for a metal hallide lamp) and small sized, having a successful niche until LED lamps appeared. Since they are very compact light sources it should be noted that heat output is very high, making the lamp unsuitable for open-air operation, especially on lower power ratings, seriously limiting flexibility. While both high pressure mercury vapour and high pressure sodium gear and fixtures can be used, the lamp works closer to designed parameters when used with inductive ballasts for sodium high-pressure vapour lamps and a suitable ignitor added on the circuit as required.
Lower rated power output gears can be used, but it is not recommended as colour reproduction and lamp lifetime will be reduced while higher powered ones damage the lamp due to over-stressing and is highly dangerous. Used lamp gears might work but old lamps are never desirable as they degrade much quicker than mercury vapour and sodium lamps. Rusted ballast may still operate but are a potential hazard while old, used lamps, may not have much useful life left and they may already exhibit some colour light emission issues. New old-stock lamps are the best choice, if available.
The lamp technology was an improvement of previously developed mercury vapour lamps. The potential for fluorescent powders was mostly exhausted by early 70s which meant that research concentrated on releasing better lamps that produced light directly from the discharge tube. This research was also carried previously but results were modest, as stable compounds with good colour reproduction were found to be quite aggressive and lead to short service life. Sodium, Scandium, Indium, Thallium were attempted as main elements that can offer a balanced light output but they required a specific balance of temperature and pressure to achieve best results. One major limitation was that certain compounds were costly or difficult to manufacture or mix in specific amounts, which meant that suitable results could not be found for many decades. In the late 70s and early 80s most major manufactures were able to center on specific technologies that reached good enough results for general lighting, with predictable performance.
The HQI-TS range was the result of research aimed at creating lower powered metal hallide lamps that had better colour reproduction and energy efficiency compared with high pressure mercury vapour lamps. The most important limiting factor was that the arc tube had to be formed more evenly at the ends and be reasonably well insulated and heat resistant to ensure reasonable performance. More advanced manufacturing tools and processes had to be developed. The arc tube was well built to resist the long term corrosive nature of hallides. It was also important to ensure less variations in arc tube geometry as well as temperature profile. This meant that heat reflecting coatings were mandatory for the arc tube. As soon as all these conditions were met, the lamp was released. Osram had superior manufacturing technology that allowed better performing lamps although they were also more expensive to manufacture due to less marketshare.
Products were quite successful on the market until the advent of the much improved ceramic tube metal hallide lamps, around mid 1990s. Although ceramic hallide lamps were much more expensive, their better colour reproduction, lamp life and efficiency meant that there were few reason to choose HQI-TS lamps. However, the higher wattage and white appearance choices made this lamp range more appreciated on the market than the Philips MHN-TD lamps, especially on markets where performance was favoured more than cost and Osram had a good presence. Although less affected than Philips , Osram HQI-TS lamp installations were experiencing a slow demise as the LED light sources were taking over the market in late 2000s.
Most manufacturers have been releasing lamps for many decades and constantly improved technology so that lamps had a stabler, predictable lifetime and slightly improved colour stability due to manufacturing progress.
Compared with Philips MHN-TD lamps, the HQI-TS range is much more diverse, offering a wider selection of wattages as well as more white colour choices. Also, another advantage of Osram products is that service lifetime is improved by around 2000 hours and that daylight colour lamps are very good for accurate daylight colour reproductions, with a light that closely mimics the ideal 5500K colour temperature standard. Osram HQI-TS lamps were not as widely used as MHN-TD lamps but they are a much better purchasing choice.