Last edited 09 Feb 2017

Lamp

Lamp 2.jpg

Contents

[edit] Introduction

The term ‘lamp’ refers specifically to a light source, typically comprising a light-emitting element contained within an outer bulb or tube, which generally emits radiation within the visible spectrum.

The term is also used more widely to describe products such as table lamps and floor lamps, although these should more correctly be referred to as light fittings. Light fittings (or sometimes light fixtures) can comprise lamps, lampholders, control gear, housings and so on.

The term bulb may also be used to describe a lamp, although, more correctly, the bulb is the outer glass part of a lamp which contains the light source.

Lamps may include a reflector and a lens to control the beam angle (or beam spread), they may be dimmable, they can have a range of brightness, beam angle and colour, and can be used to provide direct or indirect light.

Lamp intensity (or power density) is the overall power output of a lamp across the entire electromagnetic spectrum, generally expressed in Watts (W). This is not a measure of the brightness of the lamp, as some of a lamp’s output may be in non-visible parts of the electromagnetic spectrum.

Lamp brightness is expressed in lumen (lm). Illuminance is the level of light on a surface measured in lux (lx), where one lux is equal to one lumen per square metre (lm/m^2).

Lamp efficacy is the ratio of the light output to the power consumed, expressed in lumens per Watt (lm/W). Lamp efficiency is the proportion of electrical energy converted to light.

Lamp beam angle or beam spread is the angle of the cone of light emitted by reflectorised lamps, measured from the centre of the beam to the line where the intensity of the beam is 50% of the maximum.

Colour appearance refers to the visual sensation correlated with the ‘warmth’ or ‘coolness’ of the light emitted by a lamp.

[edit] Types of lamp

There are a wide variety of different types of lamp available:

[edit] Filament lamps

Filament lamps contain a tungsten wire (a filament) which is heated by an electrical current. Filament lamps may be incandescent lamps or halogen lamps.

[edit] Incandescent lamps

Incandescent lamps contain a filament within a vacuum-sealed glass bulb. The passage of electrical current through the filament causes it to glow.

[edit] Halogen lamps

Halogen lamps contain a coated filament surrounded by a halogen gas, which emits electrons when heated. They typically have a longer life and are more efficient than incandescent filament lamps.

[edit] Extra-low voltage lamps

Extra-low voltage lamps are small halogen lamps producing two or three times the light output of conventional filament lamps. They are typically powered from a separate 12 V source and have increased efficiency and lamp life. As the heating effect is lower, they can be preferable for display lighting

[edit] Discharge lamps

Discharge lamps, sometimes referred to as arc discharge lamps, discharge an electric current through a gas or gas / metal vapour mix. Discharge lamps may be fluorescent lamps or High Intensity Discharge (HID) lamps.

[edit] Fluorescent Lamps.

Fluorescent lamps discharge an electric current through an inert gas and low pressure mercury vapour to produce ultraviolet (UV) energy. This generates ultraviolet radiation, which is converted into visible light by a phosphor coating on the inner face of the glass. The type of coating determines the spectrum of light emitted.

[edit] Compact fluorescent lamps (CFL)

Compact fluorescent lamps are small diameter, single ended fluorescent lamps, bent to form a compact shape. They may have bases allowing them to be used as replacements for incandescent lamps.

[edit] High intensity discharge lamps (HID)

High intensity discharge lamps are formed by compact arc tubes which enclose gas and metal salts. When the arc has formed, the metal salts evaporate, forming plasma which increases the intensity and reduces the power consumption of the arc. HID’s are typically mercury, metal halide (MH), ceramic metal halide (CMH) or high-pressure sodium (HPS).

[edit] Xenon Arc Lamps

Xenon arc lamps contain xenon gas and emit light that is very similar to sunlight.

[edit] Light-emitting diodes LED

LEDs contain solid semi-conductor materials that convert electrical impulses into light. They may include fluorescent materials that alter the colour of the light. They have a similar efficiency to CFL’s but are longer lasting.

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