Features of Luminaires

The quality of a finished product depends on the quality of raw materials used, workmanship and the manufacturing processes adopted. The main features of the luminaires should be:

  1. OPTICAL FEATURES: The luminaire should be efficient and be able to do its function of light distribution etc effectively.

  2. MECHANICAL FEATURES: These properties depend upon the raw material used and the treatment and finishing done.

    • RAW MATERIAL: Following materials are used for luminaires:

      1. CRCA Sheet Steel: For indoor luminaires CRCA sheet steel is better than common black sheet. The basic advantages are:

        1. Basic forming operation can be carried out very easily without the risk of rupture or small cracks appearing on the surface. These cracks can give rise to corrosion.
        2. Uniform and brighter finish can be obtained.
        3. Pickling and oiling is done on CRCA steel sheets which insures no substantial rusting when procured. Black sheets on the other hand are so much rusted that heavy pickling has to be done to remove the rust scales; which leads to the formation of pits. As pits are very difficult to cover by paint, heavy pickling is not done. So in black sheets all the rust is not removed and the rust is covered by paint to give temporary bright finish, but eventually rust spreads under the surface and damage the luminaire.
      2. Sheet Aluminum: For outdoor luminaire sheet and cast aluminum is used as they are corrosion resistant. Sheet aluminum used for different luminaires differ in purity of aluminum and its hardness.

      3. Cast Aluminum: For aluminum casting an alloy of aluminum and silicon (known as LM-6) is used. This alloy is easier to cast and offer better resistance to corrosion than pure aluminum.

      4. Polystyrene: It is a polymer of styrene monomer and is used for manufacture of louvers for indoor luminaires. It is treated chemically for protection against discolouration due to UV radiation.

      5. Acrylic: Polysterene, though protected against UV radiation, still becomes slightly yellowish in course of time, but acrylic is absolutely immune from this drawback. Acrylic sheets are basically polymethyl methacrylate. In opal finish it is used for diffusers for decorative luminaires and in clear finish for streetlight luminaires.

    • MECHANICAL STRENGTH: The luminaire should be robust and of sufficient mechanical strength to withstand the normal handling, transportation, installation and maintenance. For this purpose proper thickness of sheet should be used. Also the strength can be enhanced by proper mechanical design for example by giving ribs etc.

    • CORROSION RESISTANT: The material should always be treated and finished to be corrosion resistant according to the application. When different metals are in contact, in the presence of moisture, bi-metallic corrosion results weakening the less noble metal. To avoid this following care should be taken:

      1. Avoid using together metals having widely different solution potential.
      2. Use paint or electroplating finish as separate layers between metals.
    • PAINTING AND FINISH: These are done with a view to prevent corrosion, provide high diffuse reflective surface and to give an attractive appearance. Generally stove enamelled finish (white for reflective surface and grey for other surface) is done for normal commercial and interiors and vitreous enamelled finish (white or grey) is done for use in humis environments. The following are the processes:

      • STOVE ENAMELING: first it should be insured that the surface is free from dust, dirt, rust and grease and for this following pre-treatment is carried out:

        1. De-greasing: It is done by passing tricloroethylene vapour over the material or by dipping the material in a tank containing trichloroethyline or a combination of suitable alkali solution at a particular temperature.

        2. De-rusting: After rinsing in water de-rusting is done by dipping the material in a tank containing a combination of suitable acid solution heated at a particular temperature. This process removes the oxide rust completely and the material is again rinsed in water before phosphatizing.

        3. Phosphatizing: This process not only increases the paint addition, but also inhibits spreading of the rust.

        4. Passivating or Neutralizing: After phosphatizing, the material is again rinsed in water. It is then necessary that the material is neither acidic nor alkaline. For this neutralisation is done by dipping the material in a bath of special solution.

        5. Primer Coating: After the pre-treatment process, primer coat of epoxy base zinc chromate is applied which acts as an anti-corroisive. The primer coat is baked at a particular temperature for a fixed duration depending upon the type of primer used.

        6. Final Coat: It ensures the desired optical characteristics, aesthetics and protects the luminaire from the atmoshpheric conditions. After applying the finish coat, the material is again baked at a particular temperature for a specified period of time.

      • VITREOUS ENAMELLING: This finish is only applicable to MS of special quality manufactured for this purpose and is called “Vetreous Enameling” quality steel. With vitreous enamel, final coating may be regarded as a special type of glass adhering very strongly to the surface coated. It posses all the excellent qualities associated with glass- durability at relatively high temperatures, no colour change during the life and is capable of being pigmented to give very good white colour. However it can be easily chipped off and once the coating is damaged, it cannot be repaired. Secondly, the enameling process is more expensive than stove enameling, as coating is done at higher temperature and minor production faults cannot be rectified and so construction often needs to be rigid. So this is recommended only for corroisive, excessive humid atmosphere and for operation at high temperatures.

  3. ELECTRICAL CHARECTERISTICS: The electrical characteristics of a luminaire depends mainly on the accessories used. The essential accessories used for a discharge lamp are:

    • Ballast: It is the most important part of a gas discharge lamp and should have following features:

      1. It should deliver right wattage to the lamp to ensure full lamp output and long lamp life.
      2. A right amount of pre-heat current to be allowed before the lamp ignition. Starter should be designed to allow the preheat current for a specified period of time.
      3. It should provide sufficient large voltage for the lamp ignition.
      4. Temperature rise should be within permissible limits.
      5. Power loss should be low and efficiency high.
      6. Humming noise should not be there.

      Copper wound ballast filled with polyster resin should be used as it has good heat conducting properties and is a good insulator. Also once solidified, this resin wil not melt or leak at the temperatures normally encountered.

      The polyster resin in or impregnated under vaccum condition to ensure that no air pockets are left.

    • Starter: Glow switch type starters are used for fluorescent lamps. They ensure that preheat current is allowed for the right period. The closing voltage of the switch is higher than the voltage drop in the lamp so that there is no undesirable blinking of the lamp.It should have sufficient mechanical strength. Also a suppression capacitor is used to prevent radio interference.

    • Lamp Holders: Holders should have perfect and smooth contact with the pins of the lamp cap and grip it firmly and it should be easy to remove the lamps from the holder. The fluorescent luminaires are provided with spring loaded rotor type self locking lamp holders. It should not be possible to touch the live parts after the lamp has been taken out.

    • Starter Holders: Starter holders are well designed and are of robust construction and are built for easy removal and insertion of starters.

    • Capacitors: The oil filled capacitors are used in discharge lamp circuit to improve the power factor of the installation. It should have following features:

      1. Housing should be hermetically sealed to ensure long trouble free service.
      2. Aluminum housing should be used to prevent corroison.
      3. Losses should be low.

      In order to achieve maximum efficiency of the lamp fitiing, the relative position of the condenser is very important and it should be placed at the coolest possible point inside the fitting. The 3.5 μF and 5.7 μF condenser can be used in series with the ballast which also assists in removing stroboscopic effect. The type and capacity of capacitors used are:

      For 2 × 20 W TL lamp:250 V, 4 μF condenser.
      For 1 × 40 W TL lamp:250 V, 4 μF condenser.
      For 2 × 40 W TL lamp:400 V, 3.5 μF / 250 V, 8 μF condenser.
      For 2 × 65 W TL lamp:400 V, 5.7 μF condenser.
  4. SAFETY: The rivenut empoyed for earthing should be fixed on the surface before enameling, although this means one additional operation of retrhreading after the painting. The hardware of the fitting should be carefully chosen and suitably plated and passivated. All electrical connections and cables should be adequately insulated by sleeves to prevent accidental contacts.

  5. Ease of Maintenance: 

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