Philips GLS Incandescent

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General Lighting Service (GLS) lamps or standard lightbulbs (long banned in the EU, used as reference)


  • Clear glass or diffuse glass outer bulb
  • Coiled-coil tungsten-wolfram incandescent filament supported on 1 or 2 intermediate points
  • Vacuum (15W) or gas-filled bulb (25W to 250W)
  • E14, E27 base
  • Color rendering index Ra of 100 (the filament is a true blackbody emitter)
  • Typical lifetime of 1.000 to 2.000 hours (on longer life lamps)
  • Luminous efficacy of 8 to 12 lumens/watt
  • Incandescent white (from 2700 K colour temperature)
  • Universal operating position

Lamp control gear

  • No lamp control gear required but can be used with dimmers to reduce light output

Philips GLS 60W

Best retro purpose

Flourescent lamps are the most popular and widely used lighting source. Still widely used in most indoor environments due to their high effciency and very good colour reproduction, flourescent lamp stocks and availability is still high. Millions of these lamps have been produced worldwide for decades. They are clearly suited for indoor lighting especially when paired with an electronic ballast that eliminates flicker and also increases system efficiency. Due to the great variety of lamps, there are some suggestions for use. Most flourescent lamps operate well at 25 degrees Celsius ambient temperature and have very low light output in freezing or below freezing environments but hot environments also reduce efficiency.

Super 80 lamps have been the most popular lamp type since the early 2000s and up to the present (2021). They may still be found new, are cheap and have very good performance. This lamp type is especially suited for areas that require a large amount of light. Due to the lamp's size and luminous flux, they are best suited for floodlighting although they can be just as well used for general lighting in any conditions. These lamps have a tendency of over saturating objects colour appearance which may be a desired or undesired side effect. Any interior can be well and pleasantly light with these lamps although foliage, plants, flowers are very well showcased.

90 De Luxe lamps have balanced, good colour reproduction with a slight efficiency reduction compared with Super 80 lamps. Due to their slightly higher sale price and slightly lower luminous flux, they were significantly less popular than Super 80 lamps. The major benefits of these lamps is that colour reproduction is very close to natural light, offering a highly realistic perspective on the environments. 90 De Luxe lamps can showcase fine goods, furniture, creating a pleasant, comfortable atmosphere in offices, living and dining rooms, bedrooms.

90 Graphica lamps were specialist items, high-end products that had a highly accurate colour reproduction. They were used in environments such as the printing and publishing business were comparisons and proofing of printed materials was required. These lamps had very low efficiency compared with other flourescent lamps but had a almost unique abilities for professional environments. While these lamps can be used in interior lighting and they showcase everything as is they were light by the sun on a clear day, their lower efficiency, slightly higher luminous flux loss due to aging and limited colour appearance selection make them quite unsuitable for general lighting. 90 Graphica lamps have been manufactured in very low quantities which means that stocks are scarce.

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)
A55 1CT 15W E27 15 W 120 lm Incandescent White 2700 K 100 1000 hours
A55 1CT 25W E27 25 W 220 lm Incandescent White 2700 K 100 1000 hours
A55 1CT 40W E27 40 W 415 lm Incandescent White 2700 K 100 1000 hours
A55 1CT 60W E27 60 W 710 lm Incandescent White 2700 K 100 1000 hours
A55 1CT 75W E27 75 W 930 lm Incandescent White 2700 K 100 1000 hours
A55 1CT 100W E27 100 W 1340 lm Incandescent White 2700 K 100 1000 hours
A65 1CT 150W E27 150 W 2160 lm Incandescent White 2700 K 100 1000 hours
A65 1CT 250W E27 250 W 3040 lm Incandescent White 2700 K 100 1000 hours


  • "MASTER" designation should point at better performing lamps but it is meaningless in this lamp range as they were normal lamps by the late 2000s;
  • there were 14W, 23W, 30W, the 1 meter 36W and standard 70W lamps as well but they were never as popular as the 18, 36 and 58 W ones, hence why they are ommitted; also note that lamp gears and fixtures for these wattages is quite scarce as well;
  • Neutral white colour appearance lamps were seldomly used as the 3000, 4000, 6500 K lamps offered satisfactory variety; the 3500 K lamps or neutral white were traditionally popular in the United Kingdom;

Durability and Repair-ability

Greatest features & flaws

Features Flaws
Relatively compact light source High glare risk on clear lamps
Perfect colour rendering Fragile construction, very short life
Suited for most applications Very high heat dissipation
Instant start, inexpensive Extremely high energy consumption


The TL-D range was conceived as a complete portfolio which was quite well suited for any task. While commercial lighting was the most successful market, flourescent lamps were present also in residential and industrial environments and they were highly successful. Super 80, 90 De luxe and 90 Graphica lamps were up-market products that catered to efficiency as well as good colour reproduction. Until the advent of advanced LED lamps, flourescent lamps were unsurpassed in terms of efficiency and lighting comfort. The lamp's quick restart, good light stability even on conventional, magnetic gear, and reasonably simple wiring made them easy to service although the lamp bi-pin connection was prone to failure due to lamp's handling as well as normal wear, the system was reasonably easy to repair and failures were quite obvious. The only drawback of these upper market lamps ranges was a slightly higher price than typical TL-D standard lamps and sensitivity to operating temperatures, common to all flourescent lamps. This major drawback seriously limited outdoor applications.

Super 80 lamps were advantageous due to high luminous output and low price. The wide array of colour temperatures caters to any application. Warm colours or more active daylight ambiances can be created easily. The lamps' very good stability and output ensures a long service life with minimal degradation. This was especially important compared with TL-D Standard lamps, as the older lamp type aged much quicker and had lower light output along with colour reproduction. Requirements for higher than 80 Ra colour rendering index in Europe made the lamps extremely popular and even made them as cheap or even cheaper than TL-D standard lamps due to volumes, marketing and economies of scale. This 1980's lamp had a massive impact in late 90s and early 2000s as most indoor environments became light as such.

90 De Luxe lamps were very good flourescent lamps. Combining the efficiency of Super 80 lamps with the uniform spectrum allowed by certain technologies developed for TL-D standard lamps made the 90 De Luxe lamps a near high-end choice. With very good colour reproduction, quite high system efficiency and comfortable light with similar colour appearance choices as with Super 80 and standard TL-D lamps, 90 De Luxe lamps were offering major benefits in lighting unsurpassed by previous technologies. Although De Luxe lamps were developed in late 70s they suffered from reduced system efficiency and higher price which limited their market attractiveness. The new 90 De Luxe lamps offered good enough energy efficiency and light output to be competitive which meant that these flourescent lamps started to be more successful. However, their slightly higher cost and wide availability of Super 80 lamps made 90 De Luxe lamps a quite rare presence except in more demanding commercial and residential applications.

90 Graphica lamps were high-end lamps designed for requirements of niche markets. Their efficiency was much less important than strict adherence to product manufacturing control, stability, and accurate colour reproduction. These lamps are true state-of-the-art products for situations where proofing of printed or on-screen materials is paramount and they were very successful. This product line has existed for more than 20 years and perfectly suited demanding technical requirements but is less suited for home or office environments due to price and scarcity. Low light outputs relative to other lamp types and especially to the Super 80 line seriously limits appeal even if perfect colour reproduction is a major advantage. Keep in mind that no known light source was available until these and compatible lamps from other manufacturers reached a fantastic colour rendering index of 98. Although incandescent and high intensity discharge lamps can get close with filters and special lamp types to accurate daylight reproduction, 90 Graphica lamps are truly unique.


All lamps require the same lamp gear that can be either conventional, composed of a magnetic, reactive or inductive ballast placed in series with the lamp along with a starter that preheats the lamp's filament to ensure reliable starts and low lamp stress. An electronic lamp gear, preferably with preheating, can be used to increase light output, eliminate flicker and increase the lamp's service life. Note that some cheap electronic ballasts do not actually offer preheating and start instantly the lamp, reducing the lamp's useful life. Preheating of lamps is assumed if there is any mention of a 0.5second duration on the electronic ballast label or the word preheating. Most world manufacturers released electronic control gear and some products even allowed variable dimming using special protocols.

While a dimmed flouresecent lamp is not as efficient as full power operation, there were and are some environments were such flexibility is appreciated. Note that starting and operating dimmed lamps is less reliable and the temperature balance and optimum operation conditions slightly deviate in these circumstances. Overpowering a lamp is possible but it is not advised. While Super 80 lamps are best suited for these circumstance that increase light output with some reduction in efficiency and service lamps, operation in such conditions stresses the lamp. Note that operating in cold environments, as a deviation from ideal conditions, reduces lamp current and power, making the lamp slightly unstable and dim.


A major advantage of T8 and TL-D lamps, regardless of type, is their full compatibility with systems of similar power ratings that were used with T12 lamps along with full replacement capability of any lamp type at a specific wattage. This makes it possible to test and replace many lamps of a specific wattage even mix lamps in multi-lamp fixtures to create a desired effect. Compatibility of T12 and T8 lamps was very important in the past as new T8 lamps were more efficient and used less power while being fully capable to be retrofitted on old installations.

Closed as well as open fixtures are very well suited for any lamp type. In general, open fixtures are better suited for lamps operating in warmer indoor environments while enclosed fixtures are better suited for colder environments. Despite what any datasheet may suggest, deviating higher or lower than the set 30-35 degrees Celsius lamp temperature slightly reduces efficiency. Super 80 lamps are the least affected by temperature changes as only the internal UV radiation can be influenced. 90 De Luxe and especially 90 Graphica lamps are more sensitive to additional light losses due to internal coating's temperature variation.


Flourescent lamps were an evolution of clear mercury vapour lamps. Development followed two avenues to increase efficiency, low pressure mercury vapour discharge and high pressure mercury discharge. High pressure mercury discharge created more useful light but the same deficit of no red and orange light was present so the light was still unsatisfactory. Low pressure mercury discharge is very efficient but not in outputting visible light, it is on UV-light emission. This UV-light is useless if it cannot be converted to visible light.

Flourescent powders were developed to convert UV-light into visible light. Some of these powders were capable of emitting light at some wavelengths, making specific colours to be cast around but they had to be quite ressistant to UV-light and efficient. This meant that some time passed until the advent of halophosphate based colours that made possible the first daylight T12 flourescent lamps, around late 1930s. This was a major achievement as such lamps had the capability of directly competing with incandescent lamps and offer better efficiency and longer life.

Subsequent developments improved lamp life and created a wide variety of flourescent powders that cast white light with different colour appearances from warm and neutral to cold and daylight. Higher and lower power lamps were created and standardization established. The preferred lamp gear turned from incandescent ballasting or mixed light to magnetic or reactive ballasts, which improved system efficiency. In the late 1970s, following requirements for higher energy efficiency due to the world oil crisis of 1973, there were major advances in technology.

The advent of high efficiency tri-band or tri-phosphorous lamps was the most important landmark. Successful development of flourescent powders that had peak UV to visible light conversion at blue, red, and green colours with peaks near the ideal wavelengths made it possible to release lamps with specific colour appearances. This high energy in light conversion was complemented by changes in the lamps gas's fill from argon to Krypton, reducing thermal losses with a slight increase in operating voltage and starting voltage. This was the market releases of the the highly successful T8 lamp, or TL-D lamp that dominated since the early 90s. Of course, up until this time there were improvements in cathodes design and electron emmissive coatings as well as other performance enhancing solutions but the release of the TL-D lamp was the most important moment.

Production of specialist lamps started in the 1950s with coloured lamps but also expanded to include De Luxe and specific lamps that would cater for many purposes. De Luxe lamps were an improvement of standard lamps in terms of colour reproction but was less efficient and had shorter service life due to coatings that were less stable in time than standard lamps. The advent of the tri-band TL-D flourescent lamp opened up the possibility of using part of its development to release new De Luxe lamps by combining such phosphorus coatings with previously developed ones. The result was a more stable, higher efficiency De Luxe lamp. Graphica lamps were a slight adaptation of previously developed phosphorus to TL-D lamps and their gas's fill and some experimentation in improving other aspects of operation to achieve better performance.

Manufacturing specificities

Philips flourescent lamps had very good manufacturing tolerances and the lamp's construction along with flourescent powder quality made reliable, predictable operation entirely ensured. Other world manufacturers were capable of similar performance. However, some slight differences were noticeable. For instance, Philips had slightly less powerful red phosporus than Osram, which means that entirely equivalent lamps from both manufacturers had slightly different colour appearance. On the other side, Chinese branded lamps were much inferior in terms of flourescent powder quality and colour reproduction as well as efficiency and service life.