With the increasing myopia of primary and secondary school students, more and more parents began to pay attention to the protection of children's vision. The desk lamp also plays the eye-protection card in a timely manner, without stroboscopic, no radiation, no dazzling, eliminating eye fatigue, preventing myopia and so on. It makes the parents look at the eyes and even spends several times higher than the ordinary table lamp. The price of "eye protection lamp". For many parents, as long as they are good for their children, they are more credible and not credible. Can it protect the eyesight and relieve eye fatigue like the business propaganda?
In the daily home environment, the indoor fixed lighting settings are mainly for daily living, rest and play, and the illumination level is relatively low. Moreover, because the active area will change and the observation time is not long, the adverse effects of the eye being exposed to the luminaire will not be significant. However, when people study and read at the desk, the situation is completely opposite. It takes the eyes to observe in a relatively small area for a long time. Indoor fixed lighting creates an unfavorable situation: because the distance between the eyes and the writing is relatively close, it is easy to produce shadows on the writing; the reading time is longer, the illumination is not enough, the eyes are in a state of tension; the fineness of the read text symbols requires careful eyes. Observation, low illumination and uniformity will affect the ability to distinguish. These conditions are such that the eyes will quickly reach fatigue, which is not conducive to the protection of vision. The desk lamp compensates for the lack of home lighting, and provides sufficient local illumination for work and study, which is conducive to careful observation of the eyes for a long time and slow down the fatigue.
Second, the name of "eye protection table lamp" has no scientific basis, and should be called "visual work table lamp".
The evaluation of the illumination quality of the desk lamp includes illumination level, illumination uniformity, glare control, flicker and electromagnetic radiation to the human body. The desk lamp that meets the requirements of reading and writing lighting can provide a comfortable lighting environment, and the protection of vision is self-evident. However, we cannot call these table lamps that meet the lighting requirements as "eye protection table lamps". Because it can not play a role in the treatment of myopia, but in the case of our eyes healthy, it is beneficial to the protection of vision. When the eyes are already nearsighted, the decline in vision can also be delayed. In the face of all kinds of hype, the name of "eye protection" means that consumers are dazzled and confused when they buy lamps. Therefore, for the purpose of correctly guiding consumption, the product certification of high-performance "visual work table lamp" based on standards and inspection is ready. On November 29, 2013, CQC1601-2013 "Technical Specifications for Visual Work Table Lamp Certification" and CQC16-465316-2013 "Visual Work Table Lamp Certification Rules" were officially released and implemented. Certified product (with Marked), not only meets the requirements of national mandatory standards, but also fully complies with the certification technology in terms of illumination level and uniformity, glare control, correlated color temperature, color rendering index, photobiosafety, electromagnetic radiation, flicker, noise, etc. Specification requirements. The issuance and implementation of this certification technical specification will have a positive effect on the "visual work table lamp" market specification.
Third, the visual work table lamp needs to pay attention to the technical points Visual work table lamp refers to the table lamp for reading and writing visual operations or VDT (video display terminal) visual work.
1. Photometry
1) Illuminance and uniformity illuminance should meet the requirements of GB/T 9473 illumination and uniformity. See Table 1 for specific requirements.
When the eye moves from a dark environment to a bright place, it will feel glare, and the pupil of the eye will immediately shrink to reduce the incoming light to adapt to the bright environment. This is a natural physiological adaptation phenomenon. Therefore, it is required that the illumination of the table lamp on the table should be relatively uniform, and the illumination area should cover the area of ​​the visual operation. Otherwise, the illumination is uneven in the line of sight of the eye during the visual operation, causing the eye to constantly adjust the size of the pupil. It is easy to cause visual fatigue. Two levels of illumination are specified for this, and the uniformity of illumination in each area is specified to be no more than 3, ensuring a certain degree of illumination and uniformity of illumination, and alleviating visual fatigue.
2) Shading glare is an important part of evaluating the performance of table lamps. We all have such life experience. When you meet the sun, you can't see the scene in front. When you cover your eyes with your hands, the scene in front of you is much clearer. This is because the sun's rays shine into the eyes, forming a light curtain, like a curtain in front of the scene, the scene can not be seen. When the visual work table lamp is placed on the table, and the height of the lamp body is similar to the height of the eye, if the structure size of the lamp is unreasonable, the light of the lamp overflowing into the eye will cause a light curtain. Therefore, the requirements for the table lamp, when the eye is at a height of 400 mm from the table top and 600 mm from the center of the light source, the inner wall of the light source and the reflector should not be visible.
3) Brightness of the lampshade
When the height of the light-emitting surface of the VDT visual work table lamp is less than 750mm in the normal working position, the person adopts the sitting position from any normal use position, and the VDT visual work table lamp with the upward beam of light has a translucent area of ​​the side of the lamp cover of not less than 10cm2. The brightness of the translucent surface should be between 510 cd/m2 and 170 cd/m2. The VDT vision work table lamp also has a significant amount of upward beam flux, and the upper beam flux is at least 50% of the total luminous flux.
2. Blinking The flicker of this paper is measured by the depth of the fluctuation. The wave depth is the ratio of the difference between the maximum value and the minimum value of one cycle of the light output to the sum of the maximum and minimum values ​​of the light output, expressed as a percentage. The depth of the fluctuation is also known as the percentage of flicker. IEEE PAR 1789, "Potential Health Effects of Illumination Flicker" indicates that the potential adverse effects of scintillation include the following five aspects:
- photosensitive epilepsy or scintillation-induced seizures;
- stroboscopic effects and associated significant slowing or stopping of the rotating machinery;
- Migraine or severe headache is often accompanied by nausea and visual disturbances;
- increase repetitive behavior between autistic people;
- Includes strain fatigue, eye strain, blurred vision, and traditional headaches, vision, and performance degradation in vision-related work.
The relationship between the flicker frequency and the fluctuation depth function of the low-risk and imperceptible levels of influence in IEEE PAR 1789 is shown in Figure 2. The unaffected areas are shown in green and the low-risk areas are shown in orange. The upper limit of the low-risk area is the fluctuation depth line, <flicker frequency × 0.08, which is equivalent to 2.5 times the unaffected edge.
When the desk lamp is operated at its rated voltage, the fluctuation depth of its optical output waveform shall not exceed the following limits:
- Light output waveform frequency ≤ 9Hz, 0.288%;
- 9Hz < light output waveform frequency ≤ 3125 Hz, light output waveform frequency × 0.08 / 2.5 (%); light output waveform frequency > 3125 Hz, exempt from assessment. The above flicker requirements take into account the limits of the unaffected zone.
3. The blue light hazard of the retinal blue light table lamp should meet the requirements of IEC/TR 62778. The blue light hazard category at 200 mm (0.011 radians measurement) should not exceed RG1.
4. Electromagnetic radiation to the human body The electromagnetic radiation to the human body shall comply with the requirements of IEC 62493.
The effect of electromagnetic radiation on the human body is mainly reflected in the induced current density and thermal effects of human tissues. The current density generated by the electric field (weight 0.85) is measured in accordance with IEC 62493:2009. The current density (weight 0.15) and thermal effect generated by the magnetic field are measured in accordance with CISPR 15. IEC 62311:2007 "Evaluation of Limitations of Human Electromagnetic Radiation (0Hz-300GHz) for Electronic and Electrical Equipment" A digital model of a homogeneous human body (shown in Figure 3) shows that the human body has a head diameter of 210 mm and a neck diameter of 110mm.
Figure 3 Digital model of a homogeneous human body
It is generally believed that the head of the mannequin is closest to the lighting device, and the maximum current density appears in the neck of the human body. The head of a human body model is used as a sensing part of the human body to measure the induced current, and the diameter of the neck of the human body is used. Calculate the induced current density. IEC 62493 uses the head diameter and neck diameter of a homogeneous human body as proposed in IEC 62311, as shown in Figure 4.
Figure 4 shows the diameter of the conductive ball used as the measuring device and the diameter of the neck used for the calculation.
The measuring device for the induced current density is shown in Figure 5.
The magnitude of the current density Jcap (fn) depends on the amount of parasitic capacitance between the illumination device and the conductive ball. The measured distance d in Fig. 5 is inversely proportional to the magnitude of the parasitic capacitance, and the relationship between the two is shown in Fig. 6. When the measurement distance is 30 cm, the parasitic capacitance is 3 pF. When the measurement distance is 50 cm, the parasitic capacitance is 2 pF. The smaller the measurement distance d, the larger the parasitic capacitance between the illumination device and the conductive ball; the larger the measurement distance d, the smaller the parasitic capacitance between the illumination device and the conductive ball. The IEC 62493:2009 specifies the measuring distance for different lighting devices, and the table lamp measures a distance of 30 cm.
Figure 6 is a graph showing the relationship between the measured distance d and the parasitic capacitance C.
5, noise
When the desk lamp is in normal operation, its noise shall not exceed 25dB(A).
6, safety requirements
The safety requirements for table lamp products shall comply with the provisions of GB 7000.204 and GB 7000.1.
7, electromagnetic compatibility
The radio disturbance characteristics shall comply with the requirements of GB 17743. Harmonic current should meet the requirements of GB 17625.1.
Fourth, LED vision work table lamp needs to pay attention to the problem The main points of attention of the visual work table lamp are illumination and its uniformity, shading, flicker, correlated color temperature, color rendering, photobiosafety and noise. For LED desk lamps, in addition to focusing on the elements of the visual work desk lamp described above, it is also necessary to pay attention to the following issues:
1, LED desk lamp shade
For a desk lamp using LED as a light source, the height of the table is 400 mm from the reading and writing table, and the horizontal distance from the center of the light source is 600 mm. When looking at the lamp, the light source of 2000 cd/m2 or more and the inner wall of the reflector or the light transmitting structure should not be seen.
2, the relevant color temperature
The correlated color temperature should not be higher than 4000K. The requirement of this article is mainly to consider the influence of blue light on the Sichen rhythm. High color temperature LED lamps will affect the normal morning rhythm of the human body. Figure 7 shows that the blue LED white light spectrum curve is mixed with the circadian rhythm curve, so it is not suitable to use high color temperature LED table lamps at night, especially in growth and development. Primary and secondary school students in key periods. Because the eyes of primary and secondary school students have not yet developed, the permeability of visual channels is much better than that of adults, and they are more susceptible to visual hazards. In addition, any disease in the macular area of ​​the retina is not regenerated, and the illumination of the table lamp is usually 500lx or higher. It takes a long time to use, so people, especially teenagers, should not use high color temperature LED table lamps in the evening.
Figure 7: The blue LED white light spectrum curve is mixed with the circadian rhythm curve.
3, color rendering index
The general color rendering index (Ra) should not be lower than 80. R9 should be greater than zero.
Fifth, the recommended guide for the use of visual work desk lamps
1, the position of the table lamp
Care should be taken not to be placed directly in front of the person to avoid reflection glare on the paper (see Figure 8 for an example of the position where the desk lamp is located directly in front). The position of the lamp should also be avoided to avoid the shadow of the hand (such as the right hand writing, the table lamp should be placed on the left side, see Figure 9).
Figure 8 Example of the position where the desk lamp is located directly in front
Figure 9 Example of the placement of the desk lamp to avoid the shadow of the hand
2, desktop materials and their colors
It should be made of light matt material with a reflectance of 30%-70% (the table should not be black or dark and not suitable for gloss). The table top placed on the desk lamp should be light-colored, similar to the color of the reading material, not the glass table top. The job-to-background brightness ratio depends on the difference in brightness between the normal work surface and the background work surface. For long-term paper work and improved visual fatigue, a medium-bright shade of matt work surface (shown in Figure 0) provides a soft, comfortable background.
The dark work surface, the first impression is striking, and a strong brightness ratio is formed between the paper work surface and the background of the work surface. Long-term paper work is likely to be visually fatigued (as shown in Figure 11). The shiny work surface reflects the brightness of the luminaires, ceilings and walls back to the user, possibly resulting in light curtain reflections that can be distracting or annoying (see Figure 12).
Figure 12 Glossy work surface produces light curtain reflection
3, the brightness ratio of the work surface to the surrounding and the environment
To create a comfortable lighting environment, IESNA recommends ambient and operational lighting solutions when working on desk lamps: direct/indirect lighting wall lights or low-bright ceiling mounted fixtures on the front or side of the table. The maximum brightness ratio recommended by VDT workstations in office reading and writing lighting environments is shown in Figure 13.
Figure 13 Recommended maximum brightness ratio for VDT workstations
(The values ​​connected by lines between the surfaces indicate the recommended maximum brightness ratio)
Sixth, the conclusion
The technical points of attention for visual work desk lamps include not only general safety aspects, but also photometry, flicker, electromagnetic radiation to the human body, correlated color temperature, color rendering index, photobiosafety, and noise. Consumers no longer have to worry about buying a high-performance desk lamp. The China Quality Certification Center has already certified visual work desk lamps. The quality of children's vision is caused by many factors. In addition to genetic factors, it is related to people's life rules and eye habits. Recognize the certification mark at the time of purchase to provide a healthy and comfortable lighting environment for your child's study.
A rice cooker or rice steamer is an automated kitchen appliance designed to boil or steam rice. It consists of a heat source, a cooking bowl, and a thermostat. The thermostat measures the temperature of the cooking bowl and controls the heat. Complex rice cookers may have many more sensors and other components, and may be multipurpose. Cooking rice has traditionally required constant attention to ensure the rice was cooked properly, and not burnt. Electric rice cookers automate the process by mechanically or electronically controlling heat and timing, thus freeing up a heating element on the cooking range that had to be otherwise occupied for rice cooking. Although the rice cooker does not necessarily speed up the cooking process, with an electric rice cooker the cook's involvement in cooking rice is reduced to simply measuring the rice, preparing the rice properly and using the correct amount of water. Once the rice cooker is set to cook, the rice will be cooked with no further attention.
Features:
For modern home rice cookers, the smallest single-person model cooks 1 rice cup (180 ml), whereas large models can cook 10 cups. Commercial models can cook 20 or more cups. As a possible source of confusion, model specifications and names may list either cooked or uncooked capacity. Rice roughly doubles in size during cooking; therefore, a 10 cup (uncooked) rice cooker can produce up to 20 cups of cooked rice. The prices vary greatly, depending on the capacity, features, materials used, and the country of origin.
The majority of modern electric rice cookers are equipped with a stay-warm or keep-warm feature, which keeps the rice at an optimal temperature for serving without over-cooking it. Some gas cookers also have electric stay-warm mechanism. However, the usefulness of this feature degrades over time, a microwave may be more energy efficient or better suited to reheat rice that will sit longer than four hours.
Some rice cookers use induction heating, with one or more induction heaters directly warming the pot. This can improve energy efficiency.
Most modern rice cookers use aluminium for the inner cooking bowl. There are some models that use stainless steel instead of aluminium. Various other materials, such as copper, pure carbon, ceramic, and diamond powder coating, may be used for higher heat conductivity or better taste.
The pressure-cooking models can raise the water's boiling point higher, e.g., from 100 °C at 1.0 atm up to about 110 °C at 1.4 atm, which speeds cooking. The pressure-cooking models can also be used in high altitude areas, where the boiling temperature is below 100 Celsius. Pressure cookers are also suitable for cooking brown rice (which contains oils and bran fiber that cook differently from pure white rice starch). Some pressure rice cookers have a varying pressure control mechanism (named the "dual-pressure" method) that creates repeated pressure/release cycles during the cooking.
There also exist mechanisms to collect and return the boiled over liquid to the inner rice bowl.
Many cookers now have microprocessor-controlled cooking cycles, which are often used to adjust for rice and cooking type.
Applications
Rice cookers are typically used for the preparation of plain or lightly seasoned rice. Each rice cooker model may be optimized to cook a certain type of rice best. For example, most Japanese rice cookers are optimized for cooking Japanese rice and may not be the best for other types of rice[citation needed], although cooking time can be lengthened simply by more water.
The typical method of cooking long grain rice is boil-and-strain and/or steaming method. The absorption method used in Japanese rice cookers will produce slightly different texture and taste, usually stickier rice.
Brown rice generally needs longer cooking times than white rice, unless it is broken or flourblasted (which perforates the bran).
Different varieties of rice need different cooking times, depending on their grain size, grain shape, and grain composition. There are three main types of Asian rice: Oryza sativa subsp. indica, i.e., Indian rice (long grain rice, e.g., basmati rice and Thai jasmine rice), O. sativa subsp. javanica, i.e., Java rice (large grain rice) and O. sativa subsp. japonica, i.e., Japanese rice (medium grain rice, e.g., Calrose rice, short grain rice, e.g., most Japanese rice and risotto rice).
African rice, Oryza glaberrima, is an entirely separate species, but can be cooked in the same way. Zizania is not even in the same genus, although it is often called a rice (or "water oats"); it, too, can also be cooked in a rice cooker.
A rice cooker can be used to cook many boiled or steamed granular foods, such as pot barley, bulgar wheat, and dal. Provided the ingredients have similar cooking times, a rice cooker can cook mixtures such as khichdi. Some rice cookers can be used as automated couscoussiers, cooking couscous and a stew simultaneously.
Rice Cooker
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