1st

• Reflection


  Light is reflected from the surface of a material. If the surface is shiny, or specular, such as surface of a mirror, the angle of reflection is equal to the angle of incidence.
• Diffusion


  When the surface is matte – that is, not shiny – then the reflected light will be diffused. It may be directional or totally nondirectional.
• Transmission


  When the material is transparent (clear glass), spread (etched glass), or totally diffused ( white glass), light will pass through it in a controlled mode.
• Absorption


  Light is absorbed when it is directed to an opaque material or passed through a transparent or translucent material. There will be the loss of light in either case. The amount of light absorbed is the balance of the incident light that is reflected or transmitted.
• Refraction


  The direction of light changes at the interface between the two different materials such as air and glass; this property is called refraction. Refraction is the most effective means of controlling light and is commonly used by lighting designers. This phenomenon is the basic principle of fiber optics.
• Polarization


  Light travels at high speed with waves vibrating in all planes at right angles to the direction of travel. the phenomenon wherein the waves vibrate only in one plane. Is used in lighting controls in the form of multilayered polarizing lenses (diffusers).
• Incandescent Lamps


  Produce light by the passage of an electric current through a filament, which heat it to incandescence.
• Low Intensity Discharge Lamp


  Commonly type of LID lamps is the fluorescent lamp. It contain mercury vapor. When proper voltage is applied, an electric arc is produced between the opposing electrodes, generating some visible, but mostly invisible, ultraviolet radiation. The ultraviolet radiation excites the phosphor coating on the inside of the bulb, which emits visible light.
• High Intensity Discharge (HID) lamps


  Produce high intensity light within an inner arc tube contained in outer bulb. The metallic gas within the arc tube may be mercury, sodium or combination of other metallic vapors. The outer bulb may be clear or coated with phosphor. HID lamps are classified as mercury vapor, metal halide, high pressure sodium.
• Factors to consider in selecting light sources and equipment

  • Light output
  • Intensity
  • Luminous efficacy
  • Rated lamp life
  • Luminaire efficiency
  • Lumen depreciation
  • Color temperature (Chromaticity)
  • Color rendering index (CRI)
  • Color preference index (CPI)
  • Flicker and Stroboscopic effect
  • Brightness
  • Light intensity control
  • Accessories
• Intensity


  It is expressed in candelas at various angles from the lamp or fixture. The data are usually provided by the manufacturers in the form of candlepower distribution curves.
• Luminous efficacy


  It is the light output per unit of electrical power (lpw). Theoretically, 1 Wof electricpower can be converted t0 638 lm of monochromatic green light or about 200 lmof whitelight. The efficacy of the a lamp should include the power consumed by its accessories
• Rated lamp life


  It is defined as the time elapsed when 50% of a group of lamps remain burning
• Luminaire efficiency


  It is the ratio of the total light output of the lamps versus the total light output of all lamps in the luminaire. It is expressed in percentages.
• Lumen depreciation.


  It is known as the lost of light maybe 20% to 30% of a lamp’s initial light output.
• Color temperature (Chromaticity)


  It is the color the lamp appears, expressed in kelvins (K)
• Color rendering index (CRI)


  It is a measure of the color shifts when standard color samples are illuminated by the light source, as compared with reference light source
• Color preference index (CPI)


  It is useful in expressing the color quality of a light source on a preferential basis, such as red meat, green vegetables, blue sky, pink complexions
• Flicker and Stroboscopic effect


  When a rapidly moving object is observed the clear HID lamp, theobject may appear to be at standstill or moving at lower frequencies
• Brightness


  Physically small light sources or high intensity, such as incandescent lamps, are excellent for light control, but they can too bright for visual comport.
• Light intensity control


  It can be controlled by multilevel switching or by dimming
• Accessories


  Such as ballast, starters and dimmers
• Incandescent Lamps


  Produce light by the passage of an electric current through a filament, which heat it to incandescence. (e.g. general service, reflectorized and tungsten-halogen)
• Low Intensity Discharge Lamp


  Commonly type of LID lamps is the fluorescent lamp. It contain mercury vapor. Whenproper voltage is applied, an electric arc is produced between the opposing electrodes, generating some visible, but mostly invisible, ultraviolet radiation. The ultraviolet radiationexcites the phosphor coating on the inside of the bulb, which emits visible light.
• High Intensity Discharge (HID) lamps


  Produce high intensity light within an inner arc tube contained in outer bulb. The metallic gas within the arc tube may be mercury, sodium or combination of other metallic vapors.