Tips to choose materials: How to choose the light bulbs?

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It is such a natural move to turn on the light at home. But how much do you know about the light bulb?

The packaging box of the lighting product will indicate different information such as color temperature (in K), rated light quantity (lm), and power consumption (W).

Different countries have different standards, so you will see parameters such as CRI and illuminance lx. But the light bulbs sold in Hong Kong generally only indicate the W, K and lm.

The more complete the data, consumers can understand the performance of the light bulb more. The following will explain the important parameters of lighting products one by one.


Light Bulb Base Types


Just as screws and charging cables, you need to buy it right.

The usual light bulb bases are bayonet, screw and bi-pin. Spotlights that are the hot trend in recent years, usually GU10 or GU5.3. And there are G9 and GX 53. 

The light bulb base must come with an English letter plus a number. The English letter E stands for spiral and G stands for insertion. The following numbers represent the inner diameter of the connector or the center distance of the two pins. For example, the meaning of E27 is screw type, the inner diameter of the connector is 27mm.

What is lm


Lumen (lm) is a unit to indicate the light brightness.

The brightness of a candle is 12.566 lm. The brightness of a 60W incandescent lamp is 810 lm. 65 candles can achieve the same brightness as a 60W incandescent lamp.

The brightness emitted by a light bulb is related to the wattage (Watt number) and luminous efficiency. (Brightness = Watt number X Luminous efficiency).

Traditional incandescent lamps commonly use Watt number as a reference for brightness, because the lamp manufacturers have little difference in luminous efficiency.

For modern LED light bulbs, since the luminous efficiency will vary greatly depending on the manufacturer’s technology, thus lm will be used as an accurate description of the index to avoid misleading consumers.

A traditional 60W incandescent lamp is approximately equal to a 800 lm LED light bulb. 100W incandescent lamp is equivalent to 1500 lm LED light bulb. 

The incandescent lamp invented by Edison is not in line with modern standards because of its high-power consumption, so it is necessary to understand the calculation method of the Watt number of incandescent lamps to lm. The LED light bulb has a higher galvanic rate than incandescent lamp, and also better than compact fluorescent lamp. Therefore, LED light bulb have become the mainstream. You can refer to the following list.

Traditional incandescent watts number

Watt number of traditional incandescent lamps   lm
25 250
40 450
60 800
75 1100
100 1
125 2000
150 2

What is lux


The symbol of illuminance (lux) is lx, which is the “illuminance” of the International System of Units, which represents the luminous flux per unit area.

1 lx is equal to 1 lm per square meter. Expressed in numbers: 1 lx = 1 lm / square meter = 1 candela sphericity / square meter.

Illumination at full moon night is 0.2 lx, dark bar is about 5 lx, 700 lx is needed for reading on the desk, and 1500 lx is needed for precision craftsmanship such as hand textile. As a consumer, it is sufficient to know the concept that illuminance and brightness are different.

Illuminance is the numerical result of the light emitted by the light source shining on the walls and the ground, so that the surrounding area is “illuminated”.

Simply put, the area covered by the light source is lx. For example, light A focuses on one spot with strong brightness, and light B illuminates a larger area. Even if the brightness is of B is slight less than A, the illuminance of B is still significantly higher than A.

Brightness is the numerical value of the intensity of the light emitted by the light source.

Luminous efficiency

Luminous efficiency is how many lm per watt of electricity consumed (luminous efficiency = lm divided by watts). The unit is (lm / w). High luminous efficiency = electricity.

Watt (W)

Watt is a unit that consumes electricity, and it must be written on the packaging of all light bulbs. The light emitting efficiency of the LED light bulb is much higher than that of the incandescent lamp, which proves that the LED light bulb has high lighting performance and saves power. For example, to ensure 810 lm, incandescent lamps require 60W, light pipes require 10W, and LED light bulbs require only 9.2W.

Color temperature (K)

Color temperature is an esoteric theory. When the heat blackbody radiator matches the color of the light source, it will radiate different colors of light, such as crimson, orange, yellow, white, and blue. If the color is represented by the absolute temperature of the blackbody radiator at that time, it is “absolute color temperature”. For the light color of other light sources, if the light color of the absolute color temperature of the blackbody radiator is the same, it is expressed by the color temperature value, which is the “relative color temperature”.

Generally, the color temperature refers to the relative color temperature. The unit of measurement is Kelvin Scale, and the symbol is K. Therefore, the value of 2700K and 6000K written on the light bulb package is the color temperature.

The lower the color temperature, the yellower the color, and the higher the color temperature, the whiter the color. If it is above 6500K, the color tone will be blue. When the sun is in the afternoon time, it is about 5500K. The color temperature is lower in the early morning or evening, between 2700K and 4000K.

The color temperature of incandescent lamps is about 2700K. The light source of a general light pipe can be divided into white light and yellow light. LED lights are more varied and can create a variety of styles to match different atmospheres. Low color temperature can create a warm feeling, which is suitable for home use. High color temperature is more energetic and is suitable for office use.




Color rendering (color rendering index) refers to the authenticity / realism of the colors that an object can show after being illuminated by a light source. It is also called CRI (General Color Rendering Index), or Ra.

Ra is a value between 0 and 100. If the color of the object illuminated by the light is the same as that of the sunlight, it is 100 Ra.

Conversely, if the value of Ra is low, the colors appear distorted. Therefore, everyone should choose a suitable light source with Ra value depending on different occasions. For example, a flower shop can use high Ra so that customers can clearly see the true color of flowers.

The other name of Ra is CRI. Some brands may indicate CRI> 80 or advertised high-performance CRI on the light bulb packaging.

For outdoor light sources, the Ra value is usually lower.

The average life of a light bulb

In the past, tungsten filament biliary bulbs often needed to be replaced because of their short and fragile life, which was very troublesome.

But for now, the LED technology is very mature, which can generally be used for more than 15,000 hours (or even 40,000 hours).


Special thanks: Future Lighting

(The content and pictures of this article are provided and uploaded by the author. It does not represent the opinion of the company. If there are any copyright issues, please contact us. )

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