Lamp Characteristics Required to Specify an Electrical Lamp

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Electrical lamps possess different characteristics that make them suitable for specific applications. To be able to specify the right lamp for the best application, the following lamp characteristics need to be understood:

Lamp Electrical Power
This is the electrical power consumption of the lamp as opposed to the power consumption of a system comprising lamp and ballast.

Luminous Flux/Luminous Efficiency
The luminous flux specifies the total amount of light generated by a lamp. The rated luminous flux is usually measured at a standardised measurement temperature of 25 °C in units of lumen [lm]. The ratio of luminous flux to electrical power consumption gives the luminous efficiency [lm/W]. The system luminous efficiency also includes the power consumption of the ballast.

Service Life
The average service life is normally specified, being the time by which statistically half the lamps are still working (mortality). The drop in luminous flux also needs to be taken into account.

Light Colour
The light colour describes the colour impression made by a white light source as relatively warm (ww = warm) or relatively cool (nw = intermediate, tw = cool). It is affected by the red and blue colour components in the spectrum. The typical light colors are tabulated below:

Designation Colour Temperature Appearance  Association 
ww Up to 3,300K Reddish Warm
nw 3,300K to 5,300K WhiteIntermediate
tw Above 5,300K Blue-ish Cool

Colour Rendition
The spectral components of the light determine how well various object colours can be reproduced. The higher the colour rendition index (CRI), or the lower the colour rendition group number, the better the colour rendition in comparison with the optimum reference light.

Warm-up time
Discharge lamps in particular need between 30 seconds and several minutes to warm up and output the full luminous flux. This is a critical consideration in the selection of discharge lamps for a given application.

Re-Start Time
High-pressure discharge lamps need to cool down for several minutes before they can be started again. This needs to be considered for the particular installation where the discharge lamps are required to be used.

Dimming Capability of Lamp
Apart from incandescent and halogen incandescent lamps, nowadays all fluorescent and compact fluorescent lamps can also be dimmed over almost any range. Metal halide lamps, however, are still not approved by the manufacturers for dimming, because this may have uncontrollable effects on light quality and lamp service life. The power of high pressure sodium- and mercury-vapour lamps can be varied, but only in discrete levels.

Burning Position
Manufacturers specify the permitted burning positions for their lamps. For some metal halide lamps, only certain burning positions are allowed so as to avoid unstable operating states. Compact fluorescent lamps may usually be used in any burning position, although important properties such as the luminous flux vs. temperature curve may vary with position.

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