How is light produced?
- by the passage of an electric current
- through a vapor or gas, rather than through a tungsten wire as in incandescent
What is more efficient in fluorescent lights?
- production is more efficient than electric heating methods in filament lamps.
fluorescent lamps are:
- low-pressure mercury arc discharges sources.
- an electric arc is passed between 2 cathodes, one at each end.
What happens when the electric arc is complete?
- mercury ionizes (vaporizes) to fill the inside of the bulb.
- This vapor strikes the tube wall and phosphors
- are excited and fluoresce or become luminous.
The color rendering ability of a fluorescent
lamp source is created by
- types of phosphorescent materials coated on the inside of the bulb and the
- entire actual tube structure becomes the light source.
Cold-cathode sources have
- wattage loss, more heat is developed and efficacy is lower.
What lamps are used for all fluorescent lamps?
- are coiled tungsten filaments (cathodes) at each end of the tube and have
- greater efficacy with lower cost for equal amounts of illumination.
Neon lamps sources are:
- small diameter cold-cathodes lamps that can be shaped into signage and artworks. Gases are excited instead of phosphors.
- - Cold-cathode lamps have excellent starting ability and are easily dimmed.
Fluorescent lamps require a _______ to regulate the electric current.
Three types of mechanisms available:
- preheat: the oldest type taking a few seconds to “pre” heat the circuit using a “starter”..
- instant-start: does not require a starter which simplifies the circuitry.
- rapid-start: combines the features of pre-heat and instant start. Starters are unnecessary.
- fluorescent lamps was not possible until more recent development of new
- lighting systems that rely on a balance of the appropriate starting mechanism,
- ballast and improvements in the actual lamp.
- Care should be
- taken when specifying fluorescent products due to the fact that many products
- are still available today that would not allow dimming potential.
- When working with
- older products in renovations if dimming is necessary the fixture should be
- assessed for the potential to dim.
- T12 versus T8 and T5 : this involves the amount
- of glass tube used, phosphorescent materials and wattage
- During the first 100 hours of usage the
- lumen rating of most fluorescent lamps drops by 5 %. After that lumen reduction
- is less rapid which is a valued feature for efficacy.
- This is another valued attribute of
- fluorescent lamps due to the fact that a huge range of lamp life exists from
- 7,500 hours to 24,000.
- The EPACT of 1992 established minimum efficacy
- standards for fluorescent lamps. Minimum standards for production and imports
- must have a color rendering index (CRI) of 69. Lamps with CRI ratings of 82 or
- higher are exempt from these efficacy standards.
Flicker & Strobe
- The mercury arc in a fluorescent lamp
- operates at 60hz cycles. This means it actually turns on and off 120 times per
- second. The lamp stays visible due to the “carry-over” action of the phosphors.
CRI takes into account color rendering and the quality of light over the length of life as well as operating efficiency and assumed lamp life.
High Intensity Discharge (HID) Lamps:
- light by passing an electric current through a gas or vapor operating at high
produces light using mercury vapor
- or “multi-vapor” produces light using combined
- vapors of mercury and metal halides.
High Pressure Sodium:
- produces light using combined vapors of mercury
- and sodium with the later being the dominant color source producing an orange
- tinted color.
Low-Pressure Sodium Lamps:
- for interiors due to extremely narrow spectral range…,high in yellow
Operation of HID:
- lamps require a ballast to regulate the arc current flow.
- of lamp service can occur due to a power interruption, a severe voltage dip or
- insufficient voltage maintained from the ballast.
Lamp Extinction (HID)
- is important to note that lamp extinction can require a cooling down period
- before the arch with re-strike and create light.