Glossary of Parameters for Selecting Lighting

Color rendering index, base type, bulb wattage, or protection rating. These are terms unfamiliar to the layperson, but they must be considered when choosing the right lighting. What do these terms mean? And how do they affect the functionality of individual light fixtures? We’ve prepared a handy glossary for you. 

Luminous flux

Luminous flux is one of the most important indicators of lighting sources. It precisely expresses the amount of light energy emitted by a light source in 1 second. Its value indicates how bright a particular light fixture will be, taking into account the human eye’s sensitivity to the individual colors of the light spectrum. 

The unit is the lumen (lm). It is defined as the luminous flux emitted by a light source with a luminous intensity of 1 candela within a solid angle of 1 steradian. A traditional tungsten incandescent bulb has a luminous flux of 13.5 lm/W, whereas LED bulbs have a value of around 80–100 lm/W. However, it is also important to consider the number of diodes and the color temperature of the light (see below). Filament bulbs are capable of emitting light up to a 360° angle and, thanks to the technologies used, can achieve values of up to 130 lm/W.  

Illuminance 

Illuminance is defined as the luminous flux per unit area. It is therefore the ratio of luminous flux (expressed in lm) to area (in m²). The unit is the lux (lx). This value can be easily measured using a lux meter. This important unit is then decisive when positioning a light fixture. For hallways and entryways, values around 100 lx are considered ideal; for kitchens and bedrooms, up to 350 lx;

and for workspaces, over 1,000 lx. It should be noted, however, that this is a highly relative measure. The distance of the light source from the measured surface plays an important role here. If we place a lamp 30 cm above a table, the illuminance on the table can reach 1,500 lx; however, 20 cm to the side, the intensity already drops to a lower value. While the level is set by a standard in workplaces, in homes we tend to talk about recommendations, and it always depends on subjective perception. 

Light bulb wattage

A light bulb's power consumption indicates the amount of energy supplied per unit of time. Simply put, it is a measure of the amount of electrical energy consumed by a specific light source. It is measured in watts (W). So what is this metric used for? 

Based on these values, you can calculate the energy consumed—and it’s very simple. Simply multiply the power rating by the amount of time the light bulb was connected to the power source. If the power rating is 12 W, this means that after one hour of operation, the light bulb will draw 12 W and consume 12 watt-hours (Wh). Since energy prices are often expressed in kWh, simply divide the total by 1,000. 

Example of a calculation of the daily power consumption of a 12-watt incandescent bulb: 

12 (W) × 1 (hour) = 12 Wh = 0.012 kWh

0.012 kWh × 24 hours = 0.228 kWh × 4.91 Kč (average electricity price) = 1.4 Kč = 516 Kč/year 

Color Rendering Index 

This is a measure of color rendering accuracy—that is, a light fixture’s ability to reproduce the colors of an object as compared to natural sunlight. The higher the number, the better. High-quality LED bulbs have a CRI of 80 or higher. This makes them suitable for almost any space or room. 

Socket Type

The base is the part of the light bulb into which the light source is inserted. Each light fixture has a specific base. You need to select a light bulb with the correct thread for that base. There are several types available on the market, including screw-in, bayonet, and integrated LED modules. 

E27 base—this is a classic large thread with a diameter of 27 mm. Almost all types of light bulbs are ideal for this base and can be used both indoors and around the house. 

E14 socket—this type is characterized by its smaller diameter and is often used in decorative light fixtures. The socket is primarily designed for energy-saving light bulbs. 

GU10 socket—this socket has two symmetrical prongs, each 5 mm in diameter, spaced 10 mm apart. It is a popular option that can handle voltages up to 230 V. 

Protection Rating 

The protection rating indicates a light fixture’s resistance to the ingress of foreign objects and liquids. It is denoted by the abbreviation IP, followed by a corresponding number. You can learn more about this concept in our previous article.