Guide: 4 Essential Lighting Knowledge for Buying LED Lights

Lighting design plays a crucial role in architectural projects, and the most effective outcomes are often attained through precise lighting calculations rather than relying on "rules of thumb".

Lighting systems are special, involving subjective and artistic factors, and must not only ensure the provision of basic lighting, but also create an immersive atmosphere for the architectural environment.

Below, Rice Lighting will introduce the commonly used terms and some key technical concepts of lighting systems.

1. Lumen: the basic unit of luminous flux

Similar to how electrical current is measured in amperes and water in gallons, the light output of a lamp is measured in lumens. Many people mistakenly use watts to indicate a lamp's brightness, which can lead to confusion. In the past, when incandescent bulbs were the norm, it was possible to describe brightness in watts due to a direct correlation between the lumens produced and the watts consumed. However, when comparing different types of lamps, using watts to describe brightness can cause confusion. In fact, the efficiency of converting watts to lumens varies depending on the lighting technology used. For instance, a 80W incandescent bulb, a 20W compact fluorescent lamp, and a 12W LED bulb all produce approximately the same lumen output. A common misconception about LED lighting is that it consumes less power and will therefore be dimmer when used in a room. This is caused by the habit of using watts to describe brightness, while the correct approach should be to describe it in lumens.

How can you differentiate between various types of lamps? We introduced the concept of "luminous efficacy" to describe how a lamp converts watts into lumens, which is somewhat similar to the MPG (miles per gallon) of a car, which is essentially a measure of efficiency. If the following three bulbs all produce 900 lumens, their luminous efficacy values are compared as follows:

Just like a car with a high MPG costs less per mile to fuel, a light source that produces more lumens per watt costs less energy. Therefore, upgrading to LEDs is one of the best things you can do to improve a building's energy efficiency from a financial perspective.

Lumens are valuable for describing a lamp's light output. However, we often use a different unit of measurement for the lighting required in a specific area. Imagine a scenario where 10,000 lumens of light might be enough for a small office, but in a large warehouse, their effect would be very insignificant. Thus, the concept of illuminance is employed to define the lighting needs in a constructed environment.

2. Illuminance: Lumens per unit area

The illumination required for a given space is generally expressed in illuminance values (lx) and is not affected by the size of the space. There are generally two common units of measurement for describing illuminance values:

Since illuminance is specified per unit area, the size of the room is not important. An illuminance of 50 fc means the same thing for an office of 500 square feet and 2,500 square feet. The difference is that a larger office requires more fixtures to achieve 50 fc. The Illuminating Engineering Society of North America (IESNA) provides corresponding illuminance design reference values for different space classifications in the IESNA Lighting Handbook.

In actual lighting design, illuminance will vary to a certain extent due to the different spacing of lamps and their beam shapes. However, slight differences are acceptable unless some areas are too dark or too bright. Illuminance depends not only on the lighting distribution, but also on room characteristics such as ceiling height and surface color. Manual lighting calculations are complicated, but in modern design, these processes can basically be completed automatically by software.

3. Luminosity: Beam shape of the fixture

Beam angle is another essential aspect that lighting designers consider. For example, spotlights concentrate their output into a narrow downward beam, while troffers spread their output over as large an area as possible to achieve uniform lighting.

Do not assume that two bulbs can be used in the same application just because they have the same base shape.

Even if the total lumen output is correct, a lamp with the wrong beam shape can easily cause uneven lighting. The beam shape of a lamp is three-dimensional and can be simulated by lighting design software. Because it is difficult to perfectly present a 3D beam effect on a lighting drawing, it is generally represented by a 2D beam. However, through the product model on the software, we can also simulate a 3D full beam.

4. Color Temperature and Color Rendering

Generally, we use two indicators to describe the color performance of lighting. One indicator is a description of the light source itself, and the other is a description of the effect of the light source shining on the object.

The color temperature (CCT) describes the color of the light source. Each CCT has different applications, and it is not possible to say which color is the "best",what we need is the most “suitable”.

The color rendering index (CRI) describes how faithfully the light source renders the color of objects and surfaces. The maximum CRI is 100, describing a light source that matches the quality of sunlight - no matter what the application scenario, the higher the CRI, the better.

1) Use temperature values to describe the color of lighting

Objects emit light in a characteristic color depending on their temperature. Volcanic lava looks red for this reason. The same principle applies to stars. For example, yellow stars like the sun are hotter than red stars, and blue stars are hotter than yellow stars. In physics, this behavior is described by an abstract concept called a "black body", which is an object that only emits light when heated and each temperature matches a specific color.

In principle, the color temperature of a light source is the color component of the light source compared to the color component of an absolute black body heated to a certain temperature. If the two are the same, the temperature of the absolute black body at this time is considered to be the color temperature value of the light source.

Therefore, the lamp is not actually heated to the relevant color temperature, but this simple method is used to measure in order to assign numbers to colors. If a lamp has a CCT of 4000K, it can emit the same color as a "black body" at a temperature of 4000K, but the light source itself will not reach this temperature. In most residential and commercial buildings, the CCT range is between 2700K (yellow-white) and 6500K (bluish-white).

The color of the best lighting depends on personal preference, but the following principles apply to most lighting designs for reference: Low color temperatures like 2700K are generally considered "warm" and they tend to have a relaxing effect. Warm CCT color temperature is more popular in bedrooms, hotel rooms and restaurants. Warm colors are less suitable for commercial and industrial environments, where the relaxing effect may be counterproductive. High color temperatures, such as 6500K, are considered "cool", and they tend to have a motivating effect and increase people's awareness. They are preferred in scenarios where maximum visibility is required, such as high-precision manufacturing. Using cool colors in homes and apartments may delay sleep, and some people may feel a little stressed when staying in cold color temperatures for a long time. Color temperature values (CCT) around 4000K can be considered "neutral" and relatively balanced. Neutral white light, which is close to natural light, is an ideal lighting color for offices, classrooms, kitchens and other areas where attention is required for a long time.

2) The impact of light sources on objects and surfaces

Even if two lamps have the same color temperature value (CCT), their lighting quality may be different due to different color rendering indexes (CRI) of the light sources. The concept of CRI, I also mentioned in my previous article, you can take a look if you are interested.In general, light sources can be divided into artificial light sources and natural light sources. In most cases, we are concerned with the color quality of artificial lighting forms, such as LEDs and fluorescent lamps. The introduction of the color rendering index (CRI) is to see how well the light source can reproduce the color of objects compared to daylight or sunlight (natural light sources). A CRI of 100 means that the light source is as good as sunlight. Here I will add some additional simple principles about the color rendering index (CRI). We all know that natural light (such as sunlight) is a combination of all colors in the visible light spectrum. The color of sunlight itself is white, and the color of objects in the sun is determined by the colors it reflects. For example, a red apple appears red because it absorbs all colors in the spectrum except red, which it reflects. When we use artificial light sources, such as LED lights, we try to "reproduce" the colors of natural light so that objects look like they do in natural light.

If you look closely, you'll find that a light source with a high CRI can better reproduce the color of an object because it has a more complete spectrum. If the spectral composition of our LED light is different from that of natural light, the effect of the object will be compromised.

Although incandescent and halogen bulbs have low energy efficiency, their CRI is very high, which is an ideal 100. Fluorescent lamps tend to have a lower CRI value, and low-quality lamps have a CRI of less than 70.

The CRI value of LED lights varies greatly depending on the quality of the product. Low-end products have a CRI of less than 70, while high-performance LED lights can have a CRI close to 100.

If it is an ENERGY STAR-certified lamp, the CRI is generally as low as 80, which means that you should try to find lamps with the certification label to get high-quality lighting. Products with the ENERGY STAR label mean that the lighting quality is reliable because it has passed rigorous laboratory tests.

Of course, when choosing LED bulbs, the higher the CRI, the higher the price. However, for some places, the CRI indicator is indeed very important, such as art galleries and shopping mall stores.

Thanks for reading:)

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