Osram HQL

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Standard High Pressure Mercury Lamp for general lighting with 50W, 80W, 125W (E27 base) and 125W, 250W, 400W, 700W, 1000W (E40 base)


  • Yttrium Vanadate internal coated bulb
  • Internal high pressure mercury discharge tube made out of quartz
  • E27 base or E40 base (requires matching ballast)
  • Soft glass (50 and 80W) or Hard glass (125, 250, 400, 700 and 1000W)
  • Color rendering index Ra of 39 to 50 (lower on highest wattage lamps)
  • Typical lifetime of 16.000 to 24.000 hours (lowest on highest wattage lamps)
  • Luminous efficacy of 36 to 57 lumens/watt (highest on highest wattage lamps)
  • Cool white colour designation (3800 to 4200K colour temperature)
  • Universal operating position

Lamp control gear

  • Requires external reactive inductive ballast (230V standard on Europe):
    • Osram 50, 80, 125, 250, 400, 700, 1000 types
    • May require power factor correction capacitor for balancing line load


Best retro purpose

Mercury vapour lamps were traditionally used on industrial and street lighting and they can be used on these areas although LED lamps offer much better performance with lower energy consumption. There are still some specific uses that are specific to this technology. Light appearance is cool white with a bias towards reds as well as blues, and, especially ultraviolet.

Although this is rarely specified or even mentioned in datasheets, UV-A emission is significant if the lamp is used as is, with no cover. This means that most surfaces that are painted white look even whiter in this light. Trees foliage is also emphasized, so this type of lamps are very well suited in gardens. Flowers are not as well showcased as some colours are missing except for red, orange, white, blue and violet. The amp themselves do release quite a lot of heat meaning that closed fixtures are not well suited if not specifically built for this purpose.

Houses can be properly light but such a lamp is less suited for living rooms, bedrooms but is well suited for workshops, halls or any other space that requires wide area lighting. Generally, low power lamps such as 50W are to be avoided as they are quite fragile so typical applications focus on 125 and 250 watt lamps and 400, 700, 1000W lamps are typically too large or cumbersome to be used as free standing lamps or in light fixtures. Due to the fact that fixtures are getting harder to find, outside applications such as area lighting should consider a minimal protection for lamps, meaning that floodlighting is harder than in the past. Of course, any metal-hallide and high pressure sodium fixture can be adapted, if found.

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.

Technical details

Designation Base Lamp wattage Luminous flux Colour appearance Colour Temperature Colour Rendering Index (Ra8) Life (to 50% failures)
HQL 50W/542 E27 SG E27 50 W 1800 lm Cool White 4200 K 50 24000 hours
HQL 80W/542 E27 SG E27 80 W 4000 lm Cool White 4100 K 50 24000 hours
HQL 125W/542 E27 HG E27 125 W 6300 lm Cool White 4000 K 50 24000 hours
HQL 250W/542 E40 HG E40 250 W 13000 lm Cool White 3900 K 41 24000 hours
HQL 400W/542 E40 HG E40 400 W 24000 lm Cool White 3800 K 39 24000 hours
HQL 700W/542 E40 HG E40 700 W 40000 lm Cool White 4000 K 43 16000 hours
HQL 1000W/542 E40 HG E40 1000 W 57000 lm Cool White 4000 K 43 16000 hours

Note: HG means hard glass, SG means soft glass; The 125W E40 lamp is designed differently to achieve a longer life, by using a longer internal quartz arc tube which degrades less in time.

Durability and Repair-ability

Generally, mercury vapour lamps were very durable but more modern products were released with lower typical lifetimes. This is mainly due to the fact that upto the 70s, even into the early 80s, manufacturers focused on better performing lamps but this was detrimental to sales. Many installations were left as is with extremely old lamps that were still working, despite very low light output with a greenish tint, since they were not turned off and repairing them cost more than leaving them as is. Also, keep in mind that electricity was very cheap at that time. Many lamps could still operate with broken outer bulbs and left to be blown by wind, cope with mist and frost, although they were dangerous due to UV-C output.

Compared with modern LED lamps, mercury vapour lamps fare very poorly, as they have noticeable light output and quality degradation over 10.000 hours. However, they do have advantages. Hot or cold air affects them very little and they can survive direct operation in free-standing position, meaning with the lamp suspended on wires, even for their entire operational life. Ballast can survive tens of years if properly protected against direct rain or snow exposure. A very simple circuit means that lamp servicing is straightforward and risks are similar to mains voltage operation. 125 and 250 watt lamps are very well built and they were highly popular.

Greatest features & flaws

Features Flaws
High light output in very compact package Serious risk of glare
Highlights white walls and gardens Not suited for main interior light
Mostly omni-directional light Unavoidable light flicker and some heat output
Very simple circuitry and operation Requires bulky, heavy lamp gear


These high pressure mercury vapour lamps are compact light sources that are viable for wide area lighting. Their average colour reproduction and large output means that they are better suited to outdoor lighting. Compared with flourescent lamps they were very compact, having better performance at low temperatures. A longer lifetime, that was around 10 to 15 times higher than tungsten lamps, meant that these lamps are well suited for use in places where lamp replacement was costly, as in high bay lighting and street lighting. They had similar useful life as fluorescent lamps. High pressure sodium lamps had higher light output, almost double, of mercury vapour lamps while having low quality colour reproduction. This means that mercury vapour lamps were still suited for areas where colour reproduction was moderately important and there was still an advantage from compact light sources, which means industrial and workshop lighting, sometime even commercial premises.

While it is true that lamps have an inherent flicker due to mains operation and slight changes in light output due to operation in this circumstances with mains powered conventional gear, this effect is not as pronounced. Note that also flourescent lamps that use electro-magnetic gear exhibit the same issues, although they are less pronounced as the lamp is not operating at higher pressure and being more susceptible to a certain voltage uniformity. There was no electronic high frequency gear as used on fluorescent lamps or metal hallide lamps, even if, they could be adapted. Of course, the biggest issue is that the lamp can be damaged if attempts to operate with this gear are underway such as melting of internal components when the lamp does not strike, after a sudden interruption, and a discharge occurs in the outer bulb with no way to stop it automatically.

Fixtures are generally compact, considering the light output made available, but are generally heavy due to the bulky electromagnetic gear being used. There are directional and omni-directional fixtures that are suited to various purposes. In street lighting, the well known cobra-head style lamppost was used, and they may still be available for purchase. They were only moderately effective as light covered a large area but a considerable amount of light was lost due to the fixture directing some of it upwards, with no control. Omni-directional fixtures were used in residential areas and parks, where ambience was more important than efficiency. Indoor fixtures were centered on the typical high-bay or low-bay purposes, having a metal parabolic reflector and directing most or the entire light output downwards. Other fixtures were compact, having a boxy design, with a symmetrical or asymmetrical lamp placement that was suited for flood lighting. These type of lamps were used indoor as well as outdoor, for floodlighting. There were no home designed fixtures as these lamps were not popular in home environments and were mostly used as porch lighting with a fixture design similar to street or area lighting.

Nowadays, mercury vapour lamps are still very well suited for outdoor lighting. As the number of available fixtures diminishes and only second-hand or used products are available, they may not be economically effective to purchase except when you can readily use them rather than collect them. Free standing lamps are quite capable on their own so if you need a compact light source that is highly durable and colour output is appreciated as is, then high pressure mercury vapour lamps are well suited. They are especially well suited for lighting in areas that are undergoing renewal work, workshops, gardens. Of special interest is renewals, since no modern LED lamp can output the same light spectra that dulls old painted areas and brightens newly painted ones.


These lamps are not well suited for frequent switching. They need a couple of minutes to reach maximum light output and they require a couple of minutes to restart after being turned off. The light colour and output changes from start-up to normal operation from a pink to white. A good lamp should have a strong pink light at startup, suggesting good internal coating performance. As the lamp ages, the coating degrades and light turns greenish.

The lamp requires a conventional or electro-magnetic gear of the same power output as the lamp, connected in series with a lamp. Connecting the lamp directly to mains damages it instantly as there is no current limitation. 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 influence 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.


These are the best lamps in terms of useful lifetime, colour reproduction, light output, clearly better than Philips HPL-N lamps even if Philips lamps were very popular. Chinese branded lamps are much worse in all performance and quality metrics with a greener light output and poor reproduction of oranges and reds. Reflector lamps are generally less versatile than the classic one for most purposes but they do not require any fixtures in most instances.

The best choice of wattage are the 125 and 250 watt lamps as lower wattages have quite a low light output and larger powered lamps are bulky and too powerful for most purposes. The above lamp wattages are also cheaper as they were highly popular. Electro-magnetic ballasts or conventional gears are plentiful and can be used interchangeably with all manufactured lamps for a specific wattage. Lower rated power output gears can be used, making the lamp operate dimly but higher powered ones damage the lamp due to overstressing and are dangerous.

Used lamp gears might work but old lamps are not as desirable. 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.


HWL lamps are high pressure mercury vapour lamps that have been produced, with somewhat similar properties, since the 1950s. The lamp's fluorescent coating technology dates back to around the end of 1930s while modern lamps were essentially manufactured as early as 1970s and are a result of subsequent improvements up until that time. The market for these lamps grew as industry and commercial activity recovered after the Second World War, meaning that research was justified by large sales.

The lamp technology was an improvement of previous products that used a clear envelope and had an alumino-silicate glass where the mercury discharge was constrained. Colour reproduction was nonexistent, being so low as to render people and everything natural around them as being dead. Increasing the pressure and temperature of the mercury vapour gas discharge to emit more useful light and operation in any position was possible only with the advent of quartz discharge tubes. Colour reproduction was only slightly improved but lower wattage lamps were much more efficient. Up until late in production, the clear lamp was avoided except for street lighting and some industrial applications. Subsequently, mercury vapour lamps were heavily used in street lighting and industry. Colour rendering was the highest barrier to market success. Improvements focused on colour reproduction but energy efficiency and reliability increases were areas with best results.

Development of fluorescent coatings that emit red light made the lamp more desirable although good flourescent powders were mass produced and cheap only in late 1970s. The lamps itself were running hot so fluorescent powders had to withstand temperature and UV-C exposure stress for many years while also emitting more light than the coating powder absorbed. The first generation powders had mild colour improvements but Yttrium Vanadate ones were highly successful and durable, making the lamp suited even for some indoor illumination, especially for deluxe lamps. Near the end of production deluxe lamps were very common and standard lamps such as the HPL-N were incorporating most developments specific to these top-of-the-line lamps. These improvements made high pressure mercury vapour lamps suited for industrial, commercial, street-lighting and even some occasional residential use.

The energy crisis meant that clients demanded improvements and they were focused on improving these lamps, giving rise to derivatives such as metal-hallide lamps, with much better colour reproduction and lower energy consumption. Sodium lamps were improved, culminating in the high-pressure sodium lamps that, with their yellow-orange or golden glow, dominated exterior lighting. By late 1980s mercury vapour lamps where on a market share decline that lasted more than 25 years. This can be attributed mostly to inertia in replacing fixtures that had a lifetime of around 15 years because new installations were not done after mid 1990s due to availability of compact or linear fluorescent lamps.

These lamps were not intended for home or office use and they were seldomly used as such although they were very popular in parks, gardens and street lighting, especially in Germany. Tungsten lamps had perfect colour reproduction and electric energy costs were very low. Even after the oil crisis of the early 1970s, tungsten lamps were still cheap enough and convenient to be used for general lighting. Also, these lamps did no require any gear.

Manufacturing specificities

Osram has been releasing lamps for many decades. Lamps produced in the 70s and early 80s are probably not commonly found today. In the 90s and early 2000 Osram was manufacturing lamps in Germany and other countries, while in the last years they were doing the same thing in China. Quality was not severely affected. It should be noted that mercury vapour lamps were mass manufactured and considered low-cost products, meaning that quality was not paramount. However, mercury vapour lamps were quite popular in Germany, Italy, Russia, meaning that a stable demand was present until late 2000s.

Until the manufacturing plants move to China, there were small differences in this product line as the 90s and early 2000s was using the same technology. Chinese built lamps have some slight improvements but these are more subtle than on Philips lamps. The internal coating is thinner and has a different grain size with a potentially different powder mix, improving colour rendering more than what the datasheet suggests. Lamp lumen maintenance and uniformity is improved due to a thinner coating that degrades slower and more uniformly. The lamp does not look whitish-green as on Philips lamps, which means that if you enjoy classic light output, consistency is key at Osram.

Products manufactured by Osram (Sylvania) were similar to General Electric but with a quality and consistency much above all East-European manufacturers in terms of colour rendering, light output and life. Although datasheets are bland on Osram lamps and they are harder to find, overall, they are a better investment. These differences were maintained until the end of mercury vapour lamp production in the late 2010s, even if production was switched to China. This Philips-Osram lamp difference must be experienced in person. On the other side, Philips lamps were much more popular and are easier to find.