How to Choose a Bulb (Part 1)

The bulb is the glass envelope protecting an incandescent filament, the final object is called an electric lamp. This system is intended to produce light from electricity.

By extension, the “electric lamp” is called in everyday language “electric bulb”.

There are different kinds of bulbs:

– incandescent bulb (prohibited);

– LED light bulb;

– halogen;

– neon;

– low-energy light bulb.

The different characteristics of a light bulb

A bulb is characterized by several sizes:

Power of a bulb

– Power indicates the energy consumption of the bulb expressed in watts (W).

– The higher the power, the more the lamp consumes, which does not necessarily mean that it illuminates accordingly, other parameters are involved.

– It is expressed with P=UI where P is the power in watts, U the voltage in volts and I the current in amperes.

– The energy label, from A to G, defines the energy quality of a lamp.

– The closer the value is to G, the more energy-intensive it is; the closer it is to A, the more economical it is.


– Expresses the amount of light produced by the lamp, i.e. the luminous flux in relation to the unit of power consumption.

– It is expressed in lumen per watt (lm/W).

– For example, an incandescent lamp (conventional bulb) produces about 10 lm/W, a LED lamp produces about 25 lm/W, a fluorescent lamp (low-energy bulb) produces about 80 lm/W,

– Thus, the fluorescent lamp delivers 9 times more light for the same consumption.

The lifetime of a bulb

Calculated on the basis of 3 hours usage per day and can vary from 1,000 to 15,000 hours depending on the type.

– The life of a conventional incandescent light bulb is approximately 1,000 hours or one year.

– A halogen bulb lives two to four years and an energy-saving bulb lives for more than six years.

However, it should be noted that this lifespan is impacted by the number of times the bulb is turned on and off.

– On the other hand, a voltage of 230 V will extend the life of halogen lamps.

Colour temperature of a bulb

Measured in Kelvin (K).

– Gives an indication of the apparent colour of the light.

Of the order of 2,500, this value corresponds to a warm, orange-tinged colour, which is the colour of the incandescent bulb and halogen lamp.

– On the other hand, a fluorescent tube or LED may have a colour of 6,000 or more, cold colour in the blues, very close to daylight.

Color Rendering Index (CRI) of a bulb

The colour rendering index assesses the ability to reproduce true colours.

– This CRI varies from 1 to 100 (100 being the natural colour rendering).

– We commonly speak of 3 major families of colour rendering:

◦ from 55 to 70, mediocre colour rendering, industrial use, advertising, and signage;

◦ around 85, correct colour rendering but the hues seem saturated, often used in public places and stores;

◦ higher than 90, superior colour rendering.

If you are looking for lamps with a mood colour and visual comfort, choose lamps with the highest CRI.

– This index can be lower, around 80, for functional lighting only.

This post will now continue in part 2 in our next publication to tell you more about the criteria for choosing a bulb. For example, the bulb lifetime in hours and years, consumption in watt, light force in lm/W, colour temperature, colour rendering index, the heat released, disadvantages and benefits. Stay posted and remember to leave your comments below and share this post with people in your network.

To be continued soon!

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