Light is ubiquitous in daily life, from the performance of color temperature, the energy emitted, the illuminance generated, the color rendering, the luminous efficiency and intensity, the brightness reflected into the eyes, the glare phenomenon to the light distribution curve, beam angle and shading related to lamps and lanterns. Angle, master these basic principles, you will have a deeper understanding of light sources.
1. Color temperature
Color temperature refers to the color changes that the human eye perceives when light waves are in different energies.
In the calculation of color temperature, Kelvin is used as the unit, and 0° Kelvin = -273 °C of the black body radiation is the starting point of the calculation.
The black body is heated, and as the energy increases, it will enter the realm of visible light, for example, at 2800 ° K, it emits the same color light as the light bulb, and we say that the color temperature of the light bulb is 2800 ° K.
The color temperature change in the visible light field, from low color temperature to high color temperature is orange-red –> white –> blue.
Color temperature is a numerical value that measures and identifies wavelengths. Different wavelengths of light show different colors of light, so the color temperature of the light source has a great influence on color photography, especially natural light, whose color temperature will change with time, season, and geographical location. When it is necessary to correctly restore the color of the subject, such as retaking photos or painting and calligraphy works, taking ID photos, etc. When shooting, you must pay attention to ensure that the color temperature of the light is consistent with the color temperature required by the color film.
Color temperature does not refer to the degree of hot or cold light. The application of color temperature in photography is to measure the color components contained in the light. The classic definition of color temperature refers to: when the color of the light emitted by the light source is the same as that of the black body (refers to the object that neither reflects nor transmits under the action of radiation, but absorbs all the radiation falling on it. When the black body continues to be heated, the temperature When it continues to rise, the light emitted has a certain color, and its change order is red-yellow-white-blue) When the color of the radiated light is the same at a certain temperature, the temperature of the black body is called the color temperature of the light source, referred to as color temperature.
When sunlight is irradiated at 40° above the horizon in a cloudless atmosphere, the color temperature is 5500K. In 1983, the World Organization announced this as the standard sunlight to measure the color reproducibility of camera lenses.
For a traditional film camera, in order to accurately reproduce the color of the object, the first choice is to choose a film type with the same color temperature as the light source. Color film can be divided into daylight film and light film according to color temperature. Daylight color film is suitable for shooting in sunlight with a color temperature of about 5500K, and light color film is suitable for use in light with a color temperature of 3200-3400K. In addition, the color temperature can also be adjusted through a color temperature filter or post-production.
2. Luminous flux
The luminous flux is simply the energy of visible light, which refers to the sum of all radiant energy emitted by a light source and perceived by the human eye per unit of time. It is equal to the product of the relative visibility rate of the radiant energy of a certain band per unit time.
Since the relative visibility of the human eye to different wavelengths of light is different, when the radiant power of different wavelengths of light is equal, the luminous flux is not equal.
Illuminance is the abbreviation of light intensity, which refers to the number of lumens of luminous flux per unit area of the illuminated surface, in lux (Lux or LX), 1Lux=1 lumen/square meter, which is used to indicate the intensity of light and the degree to which the physical surface area is illuminated , We often say that the desktop for reading is not bright enough, that is, the illumination is not enough.
In the case of the same area, the higher the luminous flux of the light source, the higher the lumen value, and the higher the illuminance. Generally speaking, if the working environment is required to be bright and clear, the illuminance requirements will also be high. For example, the general lighting brightness of the overall space of the study is 100 lux, but the local accent lighting during reading requires at least 600 lux, so a desk lamp can be used as a local lighting fixture.
4. Color rendering index
Due to the different types of light sources, the actual color of the object seen will also be different. The so-called color rendering refers to the authenticity of the perception of the object under the light source and the perception of sunlight. The color rendering index indicating the degree of color rendering of the light source is called the average color rendering index. The lowest is 0 and the highest is 100. We can often see the color rendering value on the outer packaging of the light bulb. Generally, the average color rendering index is above Ra80, which is basically a color rendering. Sexual light source.
5. Luminous efficiency
Luminous efficiency refers to the luminous flux output by a light source that consumes 1 watt of electricity, expressed as the ratio of luminous flux to power consumption, and its unit is lm/W. The higher the luminous efficiency, the higher the efficiency of converting electric energy into light, that is, the less electric energy is consumed to emit the same luminous flux. Therefore, when choosing a truly energy-saving light bulb, the luminous efficiency value should be used as the final judgment standard.
6. Luminous intensity
Luminous intensity represents the physical quantity of the human eye perception strength emitted by the light source in a certain direction and range, and refers to the luminous flux emitted by the light source to a certain solid angle within a unit solid angle, referred to as luminosity, in candlelight.
Luminance refers to the luminous flux emitted by the self-luminous surface in a certain direction per unit area and per unit solid angle, that is, the bright intensity of the light reflected by the light source or object seen by the eye from a certain direction. Its unit is candela per square meter (cd/m2).
Glare is uncomfortable lighting that can cause interference, discomfort, or impaired vision because the brightness in the field of view is significantly greater than the eye can accommodate, or the light source contrast is too large. There are three types of glare:
1. Direct glare: It is generated by the eyes looking directly at the light source (lighting lamps), and the brightness of the light source is too large to cause dazzling and uncomfortable.
2. Reflected glare: Reflected glare is a common reflection, which will blur the image, easily cause eye fatigue, difficult reading, and even further cause sore eyes and headaches.
3. Background glare: glare not caused by direct light or reflected light, generally because the light source from the background environment enters the eyes too much, which affects the normal vision ability.
If you want to improve the glare in the environment, you can start from the following aspects:
1. Pay attention to the installation position of the design lamps, hide the excessively concentrated light source, and then use the reflection of the lamps to export the light source. Yilin Lighting ilin has always advocated the lighting design method of seeing the light but not the light, so that you can see the lighting but feel the lighting.
2. Use the semi-transparent lampshade material to weaken and disperse the excessively concentrated light source.
3. Use grid-type lighting fixtures to avoid looking directly at the light source.
4. The direction of light projection should be as perpendicular to the general horizontal direction of the human eye as possible.
5. For the desktop and book paper used for reading, avoid using materials that are easy to reflect light to reduce reflective glare.
9. Light distribution curve, camdlepower distribution curves
The light distribution curve refers to the light distribution state of the luminaire, which means that after the luminous body is coated with other media, the original luminous angle is changed by penetration or refraction, and the light drawn at 360° vertical, horizontal or oblique angles. Angle and intensity, but the common light distribution curve mostly refers to the vertical light distribution curve. From the light distribution diagram of the light distribution curve, it can be known that the light properties of the light-emitting lamps are direct, indirect or other light distribution ratios, which is helpful for professional lighting designers to calculate the illuminance and light source distribution.
10. Beam angle
Generally, the light source directly below the light source is the brightest, corresponding to the main axis of the light beam with the strongest luminous intensity. The angle formed by 50% of the luminous intensity on both sides of the main axis of the beam is called the beam angle, and the angle formed by the darker periphery is called the light distribution angle. Generally speaking, the light source of the projection light is concentrated, the beam angle is about 30°, and the ceiling light can reach about 140°. The size of the beam angle is affected by the relative position of the bulb and the lampshade.
11. Shading angle
The shading angle of a lamp refers to the angle formed by the tangent of the edge of the light outlet of the lamp and the level passing through the center of the light source. Under normal horizontal line of sight, in order to prevent direct glare caused by high brightness, the shading angle is generally greater than 30°, and 45° is considered to be the most comfortable angle.