The higher the CRI, the lower the light efficiency?

In the parameters of LED chips, there are two seesaws: if the CRI (color rendering index) is increased, the light efficiency will decrease, while the color temperature is low, the lighting efficiency has also decreased. This is not the fault of LED manufacturers, it is determined by the physical laws of the LED chips.

1、 The higher the CRI, the lower the light efficiency

The most common solution for LED chips is blue light chip+yellow fluorescent powder. Blue light hits the yellow fluorescent powder, mixing with white light. But the light mixed in this way lacks red in the spectrum, so the color rendering is poor (Ra is usually only 70-80).

To improve color rendering, red color needs to be added to the spectrum. The mainstream practice is to add red fluorescent powder. But the conversion efficiency of red fluorescent powder is much lower than that of yellow fluorescent powder. The same blue light chip can produce 100 lumens of light with yellow fluorescent powder, but replacing it with red fluorescent powder may only leave 70-80 lumens. As soon as the efficiency decreases, the light efficiency also decreases.

Under the same chip size and color temperature, if Ra is increased from 80 to 90, the light efficiency will decrease by 10% -15%; From 90 onwards, every slight increase comes at a greater cost. This is not a process issue, it is a physical limitation - the closer the spectrum of LED is to sunlight, the more red components are needed, and red phosphors are inherently inefficient.

Simple conclusion: To achieve true color (high CRI), one must accept a decrease on brightness.

2、 The warmer the CCT, the lower the light efficiency

CCT (Color temperature) is also an important factor affecting light efficiency. LED white light is generated by exciting fluorescent powder through a blue light chip. The lower the color temperature (warmer yellow), the higher the required ratio of yellow and red phosphors. And these long wavelength phosphors naturally have lower conversion efficiency than those with shorter wavelengths.

In addition, the sensitivity of the human eye to light of different wavelengths varies. The human eye is most sensitive to 555 nanometers (yellow green light) and less sensitive to both red and blue light. In low color temperature spectra, there are relatively fewer yellow green light components and more red light components. The same radiation power results in lower brightness perceived by the human eye. The light effect is calculated based on the brightness perceived by the human eye, so low color temperature light effects naturally suffer.

Under the premise of the same chip size and the same display, the light efficiency of 2700K is 15% -20% lower than that of 6500K. That is to say, warm light lamps are naturally darker than cool white light, not because the lamp is not working, but because the human eye is not sensitive to warm light.

Simple conclusion: To create a warm atmosphere (low color temperature), one must accept low brightness.

3、 How to choose? Choose according to the scene

After knowing these two rules, there is no need to worry about choosing a lamp - there is no universal lamp, only the most suitable one.

Warehousing, roads, parking lots: choose high-efficiency products (color temperature above 5000K, Ra≥80). Brightness and energy efficiency are the top priorities, color and atmosphere are not important.

Home, restaurant, hotel: Choose low color temperature and high color rendering products (color temperature 2700K-3000K, Ra ≥ 90). Atmosphere and comfort are prioritized, and a slightly lower brightness is acceptable.

Office and classroom: Choose balanced products (color temperature 4000K-5000K, Ra ≥ 90). It should be visually clear and comfortable, with a balance between visual and lighting effects.

Museums and high-end commercial photography: Choose ultimate color rendering products (color temperature 3000K-4000K, Ra ≥ 95). Color reproduction is the core, with light efficiency and cost taking a back seat.

Under the premise of the same chip size, there are two physical laws of LED chips:

--The higher the visible light, the lower the light efficiency (sacrificing efficiency for compensating red light)

--The lower the CCT, the lower the light effect (human eyes are not sensitive to warm light)

When selecting lighting fixtures in a project, it is important to first clarify what the core requirements of the space are - brightness, atmosphere, or accurate color. Only by making choices based on needs can we select truly suitable products.

Do you accept lower brightness for high display or low CCT when choosing lights?

A: Yes, atmosphere and color are more important

B: No, brightness comes first

C: Look at the project, different scenarios require different choices

Discuss your choices in the comment section.