Philips TL and TL-D

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Classic TL and TL-D fluorescent lamps


  • Halophosphate based coating internal coating (38mm T12 and 26mm T8 standard lamps)
  • G13 bi-pin base
  • Color rendering index Ra of 63 to 72
  • Typical lifetime of 13.000 hours
  • Luminous efficacy of 50 to 79 lumens/watt
  • Various white appearances (from 3500 to 6500 K colour temperature)
  • Universal operating position

Lamp control gear

  • Requires external gear and appropriate wiring:
    • Compatible reactive inductive ballast with matching power rating and starter
    • Compatible high-frequency electronic ballast with preheating (preferably)
    • May require power factor correction capacitor for reactive ballasts

Philips TL 40W

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 efficiency 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 but have very low light output in freezing or below freezing environments but hot environments also reduce efficiency.

TL lamps are the classic T12 flourescent light source that has been used for almost 80 years. Obsolete by 2000s standards, the lamp still survived in situations where performance in cold environments such as outdoor ones was appreciated as well as ones where the lamp's relative size resulted in less glare than T8 lamps. The lamp's performance was simply average as lamp end blackening is noticeable and the internal lamp coating does not have very good performance. Note that flicker is more visible than in T8 lamps. Overall, these lamps have been plentiful but they are somewhat scarcer today. They can be used where a diffuse light source is desirable. Although there were more advanced lamps that had Triphosphor coatings and better colour rendering, they were rare and the T12 54 or 765 type was a popular, standard, daylight flourescent lamp, widely used worldwide. It creates a good retro atmosphere when used in classic luminaires.

The TL-D lamps were a significant improvement of the T12 lamp and this meant that they were extremely popular. Using less power than T12 lamps they replaced them in most installations by the early 2000s. They had slightly less light output depreciation due to the lamp's gas filling and electrodes' design. As retro lamps, they create the same atmosphere as older T12 lamps, and they are widely available due to thousands of installations that used these lamps. Popular wattages are 18 and 36W, with a more pronounced market for the 36W type. The only slight issue is that T8 lamps are less suited for outdoor installations due to their preference for warmer environments.

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)
TL 20W/33-640 G13 20 W 1100 lm Cool White 4000 K 63 13000 hours
TL 20W/54-765 G13 20 W 1000 lm Cool Daylight 6500 K 72 13000 hours
TL 40W/33-640 G13 40 W 2850 lm Cool White 4000 K 63 13000 hours
TL 40W/54-765 G13 40 W 2500 lm Cool Daylight 6500 K 72 13000 hours
TL 65W/33-640 G13 65 W 4650 lm Cool White 4000 K 63 13000 hours
TL 65W/54-765 G13 65 W 4100 lm Cool Daylight 6500 K 72 13000 hours
TL-D 18W/33-640 G13 18 W 1200 lm Cool White 4000 K 63 13000 hours
TL-D 18W/54-765 G13 18 W 1050 lm Cool Daylight 6500 K 72 13000 hours
TL-D 36W/35-535 G13 36 W 3000 lm Warm White 3500 K 55 13000 hours
TL-D 36W/33-640 G13 36 W 2850 lm Cool White 4000 K 63 13000 hours
TL-D 36W/54-765 G13 36 W 2500 lm Cool Daylight 6500 K 72 13000 hours
TL-D 58W/33-640 G13 58 W 4600 lm Cool White 4000 K 63 13000 hours
TL-D 58W/54-765 G13 58 W 4000 lm Cool Daylight 6500 K 72 13000 hours


  • 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 omitted; also note that lamp gears and fixtures for these wattages is quite scarce as well;
  • Neutral white colour appearance lamps were seldomly used as 4000 and 6500 K lamps offered satisfactory variety; the 3500 K lamps or neutral white were traditionally popular in the United Kingdom;

Durability and Repair-ability

The TL or T12 lamps can be considered the most durable in physical terms although the TL-D lamps have the longest lifespan with the best performance out of this lamp selection, due to their gas fill and electrode design. Starting the lamp with cold cathodes and not operating them properly can be just as bad as a classic magnetic ballast.

The best service life can be achieved using electronic gear that has preheat. Note that TL and TL-D lamps are perfectly interchangeable on their gears as the TL-D lamp was purposefully designed to operate at reduced current on the same conventional ballast as the TL lamps.

Due to their construction, flourescent lamps cannot be truly repaired. However, if one of the end electrodes remain open due to the coil's sudden rupture as a result of a shock or any other damage, and the lamp does not have strong blackening, it can be repaired. Bridging the broken fillament lamp ends on the side that has been measured as noncontinuous with an ohmmeter, using a wire strip and soldering or careful tightening, can render the lamp operable again. However, note that the lamp is more dangerous to operate as the magnetic or electronic gear used with the lamp is stressed more to start the lamp. Some warm start electronic ballasts may be damaged if one of the lamp's end are shorted, so there is some risk involved. Lamp gears may be overheating when attempting to start the lamp for a long time, so if this occurs, consider the lamp as disposable.

Greatest features & flaws

Features Flaws
Low glare risk, uniform lighting Quite large lamps and fixtures
Widely available Mediocre service life and colour rendering
Mostly suited for indirect or ambience lighting Sensitive to operating temperature
Quick lamp start and restart, inexpensive Requires lamp gear


While commercial lighting was the most successful market, flourescent lamps were present also in residential and industrial environments and they were highly successful. Until the advent of advanced LED lamps, these flourescent lamps were cheap to operate and had good enough performance. 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 sensitivity to operating temperatures, common to all flourescent lamps, limited outdoor applications as well as indoor ones where the lamp heats too much. This major drawback seriously limited outdoor applications.

TL lamps are easily recognizable due to their large tube diameter. While not quite modern in many respects, the TL lamps were easy to exchange and had very predictable performance. While the internal coating degradation was highly visible, their colour reproduction was reasonable, especially for the popular "Cool daylight" lamp. The 40W lamp type was the most iconic, being used in commercial, industrial and some residential areas. Lamp flicker was noticeable due to the lack of an guard mounted near electrodes as in TL-D lamps. Compared with modern lamps, the TL type fares very poorly in efficiency and light quality.

The TL-D lamp range was quite successful. Although standard lamps brought mostly energy efficiency improvements, these lamp types can be desirable if they light an area where colour reproduction is not critical. Note that the both the "Cool Daylight" and "Cool White" lamps have reasonable performance although the cool white type had worse colour reproduction. Another advantage of TL-D lamps is their more compact size, allowing smaller warehousing space.


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. 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. TL, TL-D are highly sensitive to additional light losses due to internal coating's temperature variation compared with tri-phosphor Philips Super 80 or similar lamps.


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 market release of the the highly successful T8 lamp, or TL-D lamp, and subsequent replacement of most T12 or TL lamps due to energy savings made the TL-D dominate the early 90s sales. 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 as it required no changes in the fixtures or gear. This lamp holds an important place in the heritage of fluorescent lamps as it is responsible for some of the biggest advances in light output, colour rendering and energy efficiency from late 80s up to early 2000s.

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.