Nits vs Lumens vs Luminance
Luminance is an important parameter of tft screen, and it is an indicator that we can feel most intuitively. Nit, lumens, and luminance are three indicators that describe brightness. What do they mean, and which one is suitable for describing tft screen?
There are many different units and specifications to describe the luminance, such as luminous flux, luminous intensity, brightness or reflectance to describe the luminous characteristics of their products, what do they mean respectively? How to convert between different luminance units? Figure out these will help you a lot in the purchase of display products.
Luminous flux (Luminous flux): that is, the rate of light energy radiated by a light source or the rate of light flow (Flow arte), the basic amount of light for the ability to illustrate the light source, the unit is lumens (Lumen). For example, a 100-watt (W) bulb can produce 1,750lm, while a 40W cool white fluorescent tube can produce 3,150lm of luminous flux. By definition, 1lm is the luminous intensity (l) of a uniform point light source of 1cd emitted in 1 spherical degree stereo angle.
Luminous intensity (Luminous intensity, Candlepower): luminous intensity referred to as luminosity, refers to a three-dimensional angle from the light source (unit sr) radiated by the luminous flux, that is, the light source or lighting issued by the luminous flux in space in the selected direction distribution density, the unit for candlelight (Candle or Candela, cd). Luminous intensity of 1cd light source can radiate 12.57lm of luminous flux. Illuminance (luminance): the density of luminous flux received on the illuminated plane, measured by the luminous flux per unit area. 1 lm of luminous flux uniformly distributed on a surface of 1 square meter (m2), which produces 1 lux (Lux, lx) of illuminance; 1 LM of luminous flux falls on a surface of 1 square foot (ft2), whose illuminance value is 1 foot candle (Foot- candle). candle).
Luminosity or brightness
luminance or Brightness: when the human eye visually sees something, can be expressed in two ways: the first is used for higher luminous values such as light sources or lamps, directly to its luminous intensity to express; the second is used for its own non-luminous only reflecting light such as: indoor surfaces or general objects, to brightness. Luminance that is illuminated per unit area in a certain direction issued or reflected luminous intensity, to show the difference between light and dark illuminated objects, the metric system unit for candlelight / square meter (Candela/m2, cd/m2) or nits (nit), the British system unit for feet Lambert (Foot-lambert).
Reflectance or reflection factor: The brightness of a surface depends on the amount of light falling on it and the ability of the surface to reflect light; the amount of light it can reflect, and the form of distribution depends on the nature of the material surface, expressed in terms of the ratio of reflected light to incident light, known as the reflectance ratio or reflectance (%) of the material surface. A perfect black surface has a reflection ratio of 0, which means that no matter how much light falls on it, no brightness is produced, and all is absorbed; conversely, a perfect white surface has a reflection ratio of 1 (reflectance 100%, absorption 0%). To measure the reflection ratio, first, place the illuminance meter on the surface of the object to read out its surface illuminance value Ei (Incident light), and then place the illuminance value on it 5-8cm (light-sensitive part toward the surface and make sure there is no shadow blocking), you can measure its reflected illuminance value Er (Reflected light), the surface illuminance divided by the quotient of the reflected illuminance is the material surface The reflectance ratio of the material surface.
How to convert the radiated luminous flux and illuminance?
Obviously, the irradiation effect is not the same for different surface areas, so people use a luminosity to regulate the performance of the light source in this case. Illuminance is called luminosity, which is defined as the ratio of the luminous flux dφ on the surface element at a point on the light receiving surface to the area ds of the surface element at that point, and is expressed in lux, and can be written as
From the above formula can be known, as long as the LED light source luminous flux φ, and the area to be illuminated S, then in this area S of the surface, its illuminance E can be found. Therefore, illuminance can also be called the luminous flux per unit area. From the definition of illuminance and the above formula, we can get the mutual conversion relationship between φ and E, illuminance E and unit area can be calculated from the luminous flux φ:
φ = E – ds
These relationships are very important in practical applications, is often used in the basic design formula. For example: LED light source for streetlights, streetlights are known to be 10 meters high, the distance between the lights is 16 meters, to make the illumination of the road between the two lights for 20lux, each lamp LED light source to use how much luminous flux?
So, we have: φ= E – ds=20lux×200m2
Can the luminous flux φ and luminous intensity, i.e., light intensity, be converted to each other?
A point light source, assuming it is at the center of the sphere, if its luminous flux is 4π lm (≈ 12.56lm)
When the luminous intensity at any point on the sphere is 1cd, from this point onwards, we can perform the conversion between the two under the condition.
The conversion between the two is possible under the conditions.
Let’s take an example to illustrate, if it is known that the luminous intensity of an LED Iv = 5cd, its angle of emission is 60 °, ask it
What is the equivalent luminous flux? As the LED is made into a device is not really a point light source, it emits light.
There is a certain light distribution range, here is 60 °, only 1/6 of the sphere, at this time its equivalent luminous flux can be expressed as: φ = (4π × 60 ° / 360 °) lm × 360 ° ) × 5cd = 10lm, in the same luminous intensity, the greater the LED emitted angle, the greater the equivalent luminous flux, different
The same ejection angle in Iv the same time, φ with θ increases and increases.
luminous intensity Iv and illuminance E between how to convert？
First understand the following definition of illuminance: illuminance is the luminous flux dφ on the surface element at a point on the light receiving surface, and the ratio of the surface area ds, illuminance with lux as a unit, using the symbol lux, can be expressed as follows.
Obviously in the same luminous flux, the larger the area of the illuminated surface element, the smaller the illuminance, and vice versa.
If the LED luminous flux φ and the area to be irradiated, you can convert the illuminance E, if you know the LED.
If we know the luminous intensity of the LED Iv and the emitting angle θ, we can also calculate the illuminance on the surface of the surface area of S.
For example, an LED with an emission angle of 60° and a luminous intensity of Iv = 1cd, when illuminated on a plane with a normal distance of 0.1M
The illuminance can be obtained from the following steps:
From the above conversion of Iv and φ, we know that the equivalent luminous flux φ = 4π × (4π) of an LED with an emission angle of 60° and a luminous intensity of 1cd
The equivalent luminous flux φ = 4π × (60°/360°) ≈ 21m, and in the irradiation to the 0.1M distance of the surface element, the area of the illuminated surface element S
is as follows.
≈ 3.14×(0.1×0.58) 2≈0.0105M 2
If the distance is 1M, the illuminance at the irradiation angle is only 1.92lux.
In the display industry usually use nit to describe the brightness, Topcon’s BM-7 or Konica Minolta’s CA410 equipment is the industry’s main use of equipment, if there is no special to Oh request general display brightness of 260nit ~ 320nit, of course, can be customized tft display brightness, if you need, please contact us.