Lumen
The word "lumen" comes from Latin and means "light" or "luminosity". It comes from the same root as the English words "illuminate" and "luminous".
In physics and measurement, the term "lumen" was introduced to describe the visible luminous flux, i.e. how much light a source produces in the spectrum visible to the human eye. It is an SI unit based on the candela, which measures the intensity of light in a given direction.
In other words: lumen measures how much light a source emits in total, while candela measures how intense the light is at a given angle.
Luminaire manufacturers state the lumen output of their luminaires. This information is crucial when planning the lighting of a project, for example using the DiaLux program.
Often, the power rating of a luminaire is also multiplied by the lumen/watt number. The more current is applied to the LEDs, the lm/W ratio starts to decrease after a certain point. The best efficiency is at nominal current. At AD-Lux, we prefer not to extract maximum power from the luminaire, so that the temperature management of the luminaire remains better under control and the lifespan of the luminaire remains at the expected level.
WATTAGE
The watt (W) is a unit of power that measures the transfer or consumption of energy over time. It is named after the Scottish engineer James Watt, known for developing the steam engine.
1 watt = 1 joule per second (J/s)
That is, if a device consumes or produces 1 joule of energy per second, its power is 1 W.
Difference between watts and lumens:
That's why LED bulbs are energy efficient: they produce more lumens per watt, meaning they use less electricity to produce the same amount of light.
Watts alone do not indicate energy consumption – time is also needed. Energy (Wh)=Power (W)×Time (h)\text{Energy (Wh)} = \text{Power (W)} \times \text{Time (h)}Energy (Wh)=Power (W)×Time (h)
📌 Example:
💡 Summary:
The temperature of a heat-radiating source, used to describe the color of its light.
Unit: kelvin [K]. The lower this value, the redder the light and the higher the value, the bluer the light. The color temperature of gas discharge lamps and semiconductors, unlike that of heat-radiating sources, is called "correlated color temperature".
Assignment of light colors to color temperature ranges according to EN 12464-1:
Light color - color temperature [K]
warm white (w) < 3300 K
neutral white (nv) ≥ 3300 – 5300 K
daylight white (dv) > 5300 K
The color temperature can also be adjusted, changing the color of the light from yellow to daylight and vice versa.
The color rendering index of a lamp or bulb, as specified in DIN 6169: 1976 or CIE 13.3: 1995.
The general color rendering index Ra (or CRI) is a dimensionless quantity that describes the quality of a white light source in relation to the reproduction of eight different test colors (see DIN 6169 or CIE 1974) in a reference light source.
The color rendering index measures the color rendering ability of eight different colors (R1-R8) and mathematically calculates the color rendering index Ra, which is the CRI reading. These eight different colors each correspond to a specific wavelength of the color. Therefore, only these eight colors are used to determine the CRI reading.
Eight different colors are measured when defining the color rendering index CRI. From these, the Ra number is mathematically calculated, which corresponds with a certain weighting to the numbers R1, R2, R3, R4, R5, R6 R7 and R8.
As can be seen from the image above, the color rendering index is missing several colors that are common in our everyday lives. For example, bright red. For this reason, additional measurable colors (R9-R15) have been developed, but these points are not used when calculating the color rendering index Ra. Ra is still calculated with only eight colors.
Seven additional colors for which better measuring devices also measure color rendering ability. However, these colors are not used to calculate the color rendering index (Ra). Note that skin color and leaf green are also included.
Since only eight colors are used to calculate the color rendering index (CRI), it is possible in practice that two different light sources with the same color rendering index do not have the same ability to reproduce colors. One light source may be significantly better than the other. However, the CRI number does not tell you this. The biggest difference is in the color red, i.e. reference color number 9 (R9). Skin color is also often reproduced differently.
R9, what about it. Is it important?
The color R9 represents bright red. Some swear by its importance, others think it is not important, especially since it is not even taken into account when determining the color rendering index. So is it fundamentalism to say that R9 is an important measurement parameter? Or is it just interesting? Or completely useless?
At the time when the color rendering index CRI was defined, there were no LED lights. The most common light was the incandescent lamp. Its light spectrum is very different from that of LED light. The spectrum of incandescent light starts from cold tones (blue) and increases linearly towards warm tones. The light therefore also produces a lot of red light (wavelength approximately 625-740 nm) so in practice the proportion of bright red light has not even had to be taken into account.
This text was written by lighting expert Pasi Pouri.
The MacAdam value is related to chromatic aberrations and illumination accuracy. It is based on the MacAdam ellipse, which describes how sensitive the human eye is to detecting color differences between light sources.
Key points about the MacAdam value:
✅ Expressed in SDCM units (Standard Deviation of Color Matching).
✅ The lower value, the more even and high-quality lighting.
✅ The higher value, the more color deviations are visible.
| MacAdam (SDCM) | Color deviation | Quality level |
|---|---|---|
| 1–2 SDCM | The merest | High-precision, laboratory |
| 3 SDCM | The merest | Quality lighting (LED, studio) |
| 5 SDCM | Visible difference | Standard LED lamp |
| 7 SDCM | Clearly noticeable | Inconsistent color |
| >7 SDCM | Large deviation | Poor quality |
MacAdam 3 SDCM is generally the recommended value for high-quality LED lamps and display lighting, for example.
UGR (engl. Unified Glare Rating) is a meter used in lighting that evaluates the amount of glare in a space. It helps determine how disturbing or unpleasant people find the lighting. The UGR value is especially important in offices, schools and other workplaces where glare can reduce work efficiency and comfort.
Meaning and calculation of UGR value
The UGR value is based on a complex calculation formula that takes into account several factors:
Based on these factors, it is calculated how much the glare from light sources irritates the people in the room. The higher the UGR value, the greater the glare experience.
UGR < 10: There is very little or no glare. This is suitable, for example, for spaces where very soft and even lighting is needed.
UGR 10–16: Glare is low and is usually not perceived as disturbing. This is a good lighting requirement for meeting rooms or office spaces, for example.
UGR 16–19: Glare is moderate. This value is suitable for most work environments, such as open-plan offices.
UGR 19–22: Glare can be a bit disturbing, but usually still tolerable in, for example, industrial and warehouse spaces.
UGR 22–25: Glare is already noticeable and can interfere with working.
UGR > 25: Glare is very distracting and uncomfortable, and can significantly impair concentration and work.
The UGR value (Unified Glare Rating) is not measured directly from the lamp, but is calculated from certain characteristics of the lamp and the space using a mathematical formula. Calculating the UGR value requires certain information about the space, the placement of the lamps and the characteristics of the light. It is therefore a calculated quantity based on several different factors, and it cannot be directly measured with, for example, a light meter.
Here is the calculation formula:
The UGR value is calculated based on the following factors:
Since the UGR value is based on a complex formula and several different parameters, specialized lighting design programs such as DIALux, Relux or other CAD-based lighting calculation programs are often used to calculate it. These programs are entered into:
Based on this information, the program calculates the UGR value in different places of the room and gives an estimate of how disturbing the glare is from different perspectives.
Do you want to hear more? Call us and we'll come to tell you more. Or send an email.
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e-mail: adlux@adlux.fi
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