Definitions of terms and phrases commonly used in the lighting industry.
To operate discharge lamps, either fluorescent lamps or high pressure lamps, a defined ballast is necessary.
The ballast is important for two reasons:
1. It transforms the net power to the required ignition voltage to start lamps.
2. It limits the current of the discharge process.
There are two groups of ballast available:
1. The conventional ballast – based on traditional copper-iron technique, actual as low-loss versions.
2. The electronic ballast – based on modern efficient high frequency operation.
They are also available for dimming operation which is an increasing application area.
- Colour description
The colour types of fluorescent lamps are based on an international number coding system, which combine the colour rendering and the colour temperature of a lamp. 830 is deciphered:8 = First digit of the colour rendering index; Ra=80-89, tri-phosphor lamps.
30 = Two first digits of the colour temperature; 3000 K, warm white.
- Colour rendering
Colour rendering explains the ability of light sources to represent colours. The quality is measured based on eight test colours and related to a standard reference. The colour rendition of a lamp is expressed by a value as average of the eight colours = Ra. According to a defined index from the International Electrical Commission (IEC) the lamps are rated into quality classes:
Ra Classification Type of lamp 100 Maximum colour rendering Incandescent + Halogenlamps 90-99 Very good colour rendering Deluxe lamps 80-89 Good colour rendering Tri-phosphor, Fluorescent lamps 40-79 Low colour rendering Standard colours, Fluorescent lamps ≤ 40 Bad colour rendering High Pressure, Discharge lamps
For certain lighting installations a specific colour rendering is required, e.g. office lighting with 80-89.
- Colour temperature
The appearance of light colours of fluorescent lamps is based on a system defined by the International Electrical Commission (IEC); the reference to the colour temperature is related to the radiation of a black body of steel through a heating process. According to the different status during the heating process the temperature level is determined. The unit of colour temperature is Kelvin (K). The scale for light sources intended for general lighting reaches from 2,000 to approximately 10,000 K, with the following colour groups:
Colour group Temperature Type of fluorescent lamp Warm white 2,700 – 3,500 K 827 Interior, 830 Warm white, 835 Middle White Neutral white 3,500 – 5,000 K 840 White, 845 White plus Daylight 5,000 – 6,500 K 865 Daylight
The illuminance (E) is the level of luminous flux on a defined area divided by the size of the area, unit Lux (lx).
LED (Light-Emitting Diode) is a semiconductor light source. LED lamps offer long service life and high energy efficiency. The lights created is called electro luminisence.
There are some different definitions and terms in use for the “life of lamps”. Often this is depending on the lamp type, manufacturer and region. The essential definitions are:Lifetime as general term means the time during which a lamp is operating until it reaches end-of-life.
Average life means the time when 50% of the lamps have reached end-of-life, having been operated under standardized conditions. Also mentioned as rated life.
Service life means the time when in a lighting installation the amount of light falls to 80% of the initial 100 hour value. Service life is calculated on base of 10% lamp failures and 10% lumen depreciation. The operation is according to IEC/EN 60081 on a 3 hour cycle.
Lifetime with 12 hour cycle is used for discharge lamps like Fluorescent lamps or High Pressure lamps. It is an operation cycle more in line with the real time of use (one switch per day) and defined as the time when 10% of the lamps in an installation have reached end-of-life. The lumen depreciation is at this time indicated with less than 10%.
- Luminous intensity
Is the intensity of light radiated in a defined direction, unit Candela (cd).
The luminance is the light energy emitted or reflected from an object in a specific direction, unit candela per m² (cd/m²).
- Luminous efficacy
Expresses the efficiency of a light source as a result of luminous flux divided by the electrical power (wattage) used of a lamp, unit lumen per Watt (lm/W). Also mentioned as light output.
- Luminous flux
The luminous flux is the quantity of visible light radiated from a light source, unit lumen (lm).
When fluorescent lamps are operated with conventional ballast an additional equipment is needed to ignite the lamp. The starter closes the electrical circuitry around the lamp and delivers the needed starting pulse for the ignition. When the lamp is running the starter is not further included. Starters are available as glow switch starter for standard requirements and as electronic starter with comfortable characteristics for soft start with a defined pre-heating, automatic switch off when a lamp is defect, and direct re-start when new lamps are installed.
- Tri-phosphor powders
The variety of colours of fluorescent lamps are created by a mixture of three basic colour components; red, green and blue. Based on the relative balance of those the colours are defined, e.g. warm white has more red and green, daylight more blue component. The overall light appearance is giving a white impression showing the appearance of warm, white or daylight. Tri-phosphor powder delivers a good colour rendition (Ra 80-89) in combination with high luminous flux and high efficient light output.