home Metal

White LEDs. Selection of LED lamps. Spectra of light sources. Phosphor in LED

LED (Lighting Emission Diode) - LEDs with intense light emission are well known to everyone. About 10 years ago (in Russia) they made a “quiet revolution in lighting,” especially where mobility, low specific energy consumption, reliability and long service life are needed. It seemed that the ideal source of light that bikers and tourists, as well as hunters and fishermen, speleologists and climbers were eager to receive, was already “here and now.” And it is enough to extend your hand, accumulating a few killed raccoons, and there will be “peace on earth, good will to men.” Now, we can say that these 10 years were not in vain and the LED reality turned out to be interesting, diverse and provides new opportunities that had not even occurred to us before.

Rice. 2 Design of the Luxeon LED from Lumileds lighting.* (“Description and principle of operation of LED lamps” Group of Energy Saving Companies )

Rice. 3 Blue LED with monochromatic emission. . (“LED - technology, principle of operation. Pros and cons of LED.” ).

PRINCIPLE OF OPERATION .

An LED is primarily a diode. That is, a kind of cunning pebble with a p-n junction inside. In other words, the contact of two semiconductors with different types conductivity. Which, under certain conditions, emits light through the process of recombination (mutual constructive suicide) of electrons and holes.
Typically, the greater the current through an LED, the more electrons and holes enter the recombination zone per unit time and more light is emitted at the output. But the current cannot be greatly increased - due to the internal resistance of the semiconductor and the p-n junction, the LED may overheat, which leads to its accelerated aging or failure.
To get meaningful luminous flux, create multilayer semiconductor structures - heterostructures. For the development of semiconductor heterostructures for high-speed optoelectronics, Zhores Alferov, a Russian physicist, received the Nobel Prize in 2000.

TWO WORDS FOR THE STORY.

The first red semiconductor emitters for industrial use were produced in 1962. In the 60s and 70s, LEDs based on gallium phosphide and arsenide were created, emitting in the yellow-green, yellow and red regions of the spectrum. They were used in light indicators and alarm systems. In 1993, the Nichia company (Japan) created the first high-brightness blue LED. Almost immediately, LED RGB devices appeared, since blue, red and green colors made it possible to obtain any color, including white. White phosphor LEDs first appeared in 1996. Subsequently, the technology developed rapidly and by 2005, the luminous output of LEDs reached more than 100 lm/W.

WHITE LIGHT.

A conventional color LED emits a narrow spectrum of light waves (monochromatic radiation). This is good for alarm devices. And for lighting we need white LEDs and use different technologies..
For example, color mixing using RGB technology. Red, blue and green LEDs are densely placed on one matrix, the radiation of which is mixed using an optical system, such as a lens. The result is white light.

Rice. 4 Spectrum RGB radiation LED. ("Wikipedia")

Or, let’s say, a phosphor is used, or more precisely, several phosphors are applied to an LED and, as a result of mixing colors, white or close to white light is obtained. White LEDs with phosphors are cheaper than RGB matrices, which makes them possible to use for lighting.

Rice. 5 Emission spectrum of a white LED with a phosphor.* (Wikipedia)

Rice. 6 White LED with phosphor. Diagram of one of the white LED designs.

MRSV - printed circuit board with high thermal conductivity. * ("Wikipedia")

The current-voltage characteristic of LEDs in the forward direction is nonlinear and the current begins to flow from a certain threshold voltage. In the main modes of LED emission, the current depends exponentially on the voltage and small changes in voltage lead to large changes in current. And since the light output is directly proportional to the current, the brightness of the LED is unstable. Therefore, the current has to be stabilized. The brightness of LEDs can, for example, be adjusted using pulse width modulation (PWM), which requires an electronic device that supplies pulsed high-frequency signals to the LED. Unlike incandescent lamps, the color temperature of LEDs changes very little when dimming .

Advantages and disadvantages of phosphor LEDs.

In an LED, unlike an incandescent or fluorescent lamp, electricity is converted directly into light radiation, and the losses are therefore relatively small.

The main advantage of white LEDs is high efficiency, low specific energy consumption and high luminous efficiency - 160-170 Lumens/Watt.
High reliability and long service life.
The light weight and size of LEDs allow them to be used in small-sized portable flashlights.
The absence of ultraviolet and infrared radiation in the spectrum allows the use LED lightening without harmful consequences, since ultraviolet radiation, especially in the presence of ozone, has a strong effect on organic matter, and infrared radiation may cause burns.
The specific power density indicator, which characterizes the luminous flux density, of a standard fluorescent lamp is 0.1-0.2 W/cm², and for a modern white LED it is about 50 W/cm².
Work at negative temperatures without reduction, and often with improvement of parameters.
LEDs are inertia-free light sources; they do not require time to warm up or turn off, such as fluorescent lamps, and the number of on and off cycles does not affect their reliability.
The LED is mechanically robust and extremely reliable.
Easy to adjust brightness.
LED is a low-voltage electrical device, and therefore safe.
Low fire hazard, can be used in explosive environments.
Moisture resistance, resistance to aggressive environments.

But there are also minor drawbacks:

White LEDs are more expensive and more complex to produce than incandescent lamps, although their price is gradually decreasing.
Low quality of color rendering, which, however, is gradually improving.
Powerful LEDs require a good cooling system.
Rapid deterioration and even failure at elevated temperatures external environment more than 60 - 80°C.
Phosphors also do not like high temperatures, because... the conversion coefficient and spectral characteristics of the phosphor deteriorate.
The LED housing is made of optically transparent silicone plastic or epoxy resin, which ages and under the influence of temperature fades and turns yellow, absorbing part of the light flux.
Modern, powerful, ultra-bright LEDs can blind and damage a person’s vision.
The contacts are susceptible to corrosion failures. Reflectors (usually made of plastic, coated with a thin layer of aluminum), at elevated temperatures, deteriorate their properties over time, and the brightness and quality of the emitted light gradually deteriorate.

REAL LIFE OF WHITE LEDS.

Rice. 7 Reduction of light output during operation and failure behavior of incandescent lamps (INC), fluorescent lamps (FL), high-intensity discharge lamps (HID) and LED lamps (not to scale, typical curves are shown).

Magazine "Time of Electronics", Article "Determining the service life of LEDs"
Written by Eric Richman (EricRichman), Senior Researcher,PacificNorthwestNationalLaboratories (PNNL)

We have known about the 100,000 hour service life of LEDs for many years. What is it really like?
“In the early days of LEDs, the most commonly reported operating life was 100,000 hours. However, no one has been able to explain where this magic number came from. Most likely, it was dictated by the market, not science. The first LED manufacturer to indicate the service life based on real technical parameters was Philips Lumileds, with its brainchild, the Luxeon LED. The durability of the first Luxeon devices, with a specified drive current of 350 mA and a junction temperature of 90 degrees Celsius, was estimated at 50,000 hours. This means that after 50,000 hours of operation of the LED under given conditions, its luminous flux will decrease to 70% of the original.”
Article “Uncharted Waters: Determining the Durability of LED Luminaires”, Magazine "Time of Electronics", Timur Nabiev.

Currently, there is no standard defining what “service life” actually means for LEDs. There are also no standards that quantify the color change of an LED over time. It is not defined how the LED should operate after this period. Some leading companies have been forced to define their own criteria for service life. For example, two threshold values of luminous flux were selected: - 30% and 50%, upon reaching which the LED is considered to be out of order. And these meanings depend on perception by the human eye emitted light.
1) - 30% reduction in luminous flux of reflected LED light. That is, when an LED flashlight illuminates the road, surrounding objects, etc.
2) - 50% reduction in luminous flux when direct light is used, for example in traffic lights, road signs, side lights of cars....
And other first-line companies choose only one threshold value - 50%.
Moreover, the degradation of LEDs and LED lights occurs at all levels, starting with p-n junction and ending with the transparent front plastic lens of the flashlight housing. Moreover, low-power signal and indicator LEDs can serve for decades. And ultra-bright modern LEDs, which often work under intense conditions, both in current and temperature, lose their brightness much faster. Thus, the real service life of high-quality modern LEDs is from several months to five to six years in continuous operation. For example, Petzl claims a service life of its LEDs in flashlights of at least 5,000 hours. By the way, leading companies often claim a shorter service life for their devices than those of “super-duper-budget”, often Asian manufacturers, who simply increase the current level and achieve a bright glow. When buying flashlights, all the characteristics of the LEDs correspond to the passport, in which they always write about the magic 100,000 hours. But the actual service life of such LEDs may not exceed 1000...1500 hours and during this time the luminous flux decreases by at least 2 times.

BATTERIES AND ACCUMULATORS.

During operation, batteries and accumulators are discharged, the supply voltage decreases, the brightness of the LEDs and the effective luminous flux gradually decreases.

Brightness decrease curve during natural battery discharge.

Electronically adjustable brightness. Illumination of 0.25 lux is measured at a distance of 2 meters from the lamp. (This is the illumination provided by the moon during a full moon).

To improve the effective light output, electronic regulation (stabilization) of the supply voltage is used. The current strength is controlled by a special microcircuit, which ensures stable brightness throughout the entire operating time. The idea was first developed by Petzl. Thanks to electronic circuit, the lights have stable characteristics throughout the entire operating time, and then go into emergency mode (0.25 lux). A brightness of 0.25 lux is the illumination produced by a full moon high above the horizon on a clear day.

Optimal power sources.

1. For LED flashlights today, these are of course alkaline or lithium (lithium-ion) disposable batteries. Lithium batteries are lightweight, have high capacity and perform well in low temperatures. These are, for example, Li-MnO2 batteries CR123 or CR2 with a voltage of 3V or Li-FeS2 (lithium iron disulfide) batteries with a voltage of 1.5V, but not all LED lights are compatible with lithium batteries - please check the instructions.
2. Batteries.

Characteristics	Nickel-cadmium	Nickel metal hydride	Lithium- ionic
Rated voltage, V
Typical capacity, Ah
Specific energy: weight, Wh/kg volumetric, Wh/dm3	30 - 60 100 -170	40 - 80 150 -240	100 - 180 250 - 400
Maximum constant discharge current, up to	5 (10) WITH	3 WITH	2 WITH
Charge mode	Standard: current 0.1 WITH 16 hours Accelerated: current 0.3 WITH 3-4h Fast: current 1 WITH~1 h	Standard: current 0.1 WITH 16 hours Accelerated: current 0.3 WITH 3-4h Fast: current 1 WITH~1 h	Charge current 0.1-1 WITH up to 4.1-4.2 V, then at constant voltage
Capacity return coefficient (Discharge/Charge)
Operating temperature range, ºС
Self-discharge (in%): in 1 month in 12 months			4 - 5 10 - 20

Current 1C means a current numerically equal to the rated capacity.

* From the article: A.A. Taganova “LITHIUM CURRENT SOURCES FOR PORTABLE ELECTRONIC EQUIPMENT”

Nickel-cadmium (NiCd) have a small weight and dimensions, poor environmental friendliness - cadmium is a terribly harmful metal to health. Explosive with a durable and sealed housing, having microvalves for automatic release of gases, but, at the same time, fairly high reliability and high charging and discharging currents. They are often used in on-board equipment and for devices that consume a lot of power, such as diving lights. The only type of battery that can be stored discharged, unlike nickel-metal hydride (Ni-MH) batteries, which must be stored fully charged, and lithium-ion batteries (Li-ion), which must be stored at 40% charge on battery capacity
Nickel metal hydride (Ni-MH) were developed to replace nickel-cadmium (NiCd). NiMH batteries are practically free of the “memory effect” and complete discharge is not often required. Environmentally friendly. The most favorable operating mode: low current charge, 0.1 rated capacity, charging time - 15-16 hours (manufacturer's recommendation). It is recommended to store batteries fully charged in the refrigerator, but not below 0 C?. They provide a 40-50 percent advantage in specific energy intensity compared to the previous favorite - NiCd. They have significant potential for increasing energy density. Friendly to environment- contain only moderate toxins that can be recycled. Inexpensive. Available in a wide range of sizes, parameters and performance characteristics.

DIMENSIONS AND FLASHING LIGHTS.

12) TL-LD1000 CatEye

13) RAPID 1 (TL-LD611-F)CatEye

European safety practice involves the use of not only rear, but also front side lights.
Rapid 1 front (white) and rear (red) lights, with battery recharging function via USB port and charge level indicator. The high power of the flashlight is achieved by using an SMD LED and OptiCube ™ technology. The shimmer of CatEye Rapid 1 attracts the attention of motorists and passers-by.
4 operating modes provide optimal selection of parameters, both at night and during the day. CatEye Rapid 1 comes with a low profile SP-12 Flextight™ bracket, which is compatible with all new RM-1.

Operating time: 5 hours (continuous mode)

25 hours (fast and pulse modes)

40 hours (flashing mode)

Lighting memory mode (last mode you turned on)

Li-ion battery USB - rechargeable

Weight about 41 g. with mount and battery

Clip for clothes.

14) SOLAR (SL-LD210)CatEye

The cyclist must be visible not only from the back, but also from oncoming traffic, not only at night, but also during the day - with the side light on.

One 5mm LED turns on automatically in flashing mode when you start driving in the dark. The built-in solar battery charges within 2 hours in good weather conditions and provides up to 5 hours of operation. Available in front and rear mounting models, comes with the new Flextight™ bracket. Weight 44 g. including bracket and battery

DYNAMO - LANTERNS (BUGS).

15) BLUEBIRD

3- LEDs, brightness 6 lm, 3 modes, two constant (1LED and 3LED), one flashing (3LED), operation after recharging: - about 40 minutes (3LED); - about 90 minutes (1LED), weight with handlebar mount 115g.

Impression:

Well, a very good flashlight, IMHO, both for the size on a bicycle and for lighting in “manual mode” in a tent, at a rest stop, and in general. In civilized urban conditions, when general lighting Yes, even if you have good eyesight, it can even be the main flashlight, especially if the road is known. The speaker turns easily, does not make much noise, and the battery charges quickly. Shines a good white light. OK!

16) Charger Energenie EG-PC-005 for mobile phones with manual drive and flashlight. Installed on a bicycle.

Energy is generated using a dynamo with a crank. Rotating the handle for three minutes charges the mobile phone for at least 8 minutes of talk time. Rotating the crank for 10 minutes provides bright light for at least 50 minutes.

Specifications

Output voltage - 4.0-5.5V
Outgoing current up to 400 mA
Built-in Ni-MH rechargeable 80 mAH battery allows for at least 500 full recharges
2 flashlights:
-head: LED, at maximum charge illuminates up to 10 meters.
-rear: red LED.
Two modes: constant light (3LED), - strobe (3LED)
Net weight 0.2 kg
Contents of delivery

Energenie EG-PC-005 mobile phone charger with manual drive, bike mount and front flashlight
rear light with 1.2m cable
cable for Nokia phones
6 adapters for other phones

Impression:

Not a bad size, suitable for lighting in a tent and for all kinds of household needs. LEDs are not the best - with a clear bluish tint, which is not gut. Unfortunately, the battery has some difficulty coping with a double load (3LED) in front and a red light in the back - and “sit down” quickly enough. I had to turn off and throw out the red tail light and, IMHO, it got better (longer). The speaker lever is easy to turn, there is not much noise, and its own battery charges without problems. I had to charge both my mobile phone and my e-reader while traveling. With some persistence and patience, this can be done, but it will take some work. When the flashlight is operating under an external load, the force on the lever will increase significantly and you will have to sweat a little. But the overall assessment of this device is a useful thing.

17) Charger Energenie EG-SC-001 for mobile phones with a battery charged from light and from the mains and with a built-in LED flashlight.

The presence of a USB connector allows you to quickly charge the built-in battery, which is equipped with protection against overcharge, deep discharge, overload and short circuit. If the battery is low, the warning system is activated. Has a built-in LED flashlight.

Charges the following mobile phones and is equipped with the following connectors: Nokia 6101 and 8210 series, Samsung A288 series, Mini USB 5pin, Sony Ericsson K750 series, Micro-USB.

Solar cells Energenie EG-SC-001 allows you to charge mobile devices while hiking, of course in sunny weather.
Specifications

outgoing voltage - 5.4V
outgoing current up to 1400 mA
built-in Li-ion rechargeable battery 2000 mAH allows at least 500 full recharges
built-in USB connector 5-6V
bright LED flashlight
dimensions: 116*49*26 mm
weight 130 g

Contents of delivery

Charger
AC220V-DC5V USB Power Adapter A black
5 adapters for charging mobile phones
USB connection cable.

Please enable JavaScript to view the

Ecology of consumption. Ideally, a spectrophotometer is needed to assess the quality of the lamp's emission spectrum. As a last resort, you can use spectrophotometers for profiling/calibrating monitors (for example, ColorMunki) - if you have such a device.

Ideally, a spectrophotometer is needed to assess the quality of the lamp's emission spectrum. As a last resort, you can use spectrophotometers for profiling/calibrating monitors (for example, ColorMunki) - if you have such a device. There is no point in buying spectrophotometers at home to evaluate lamps; they cost from hundreds to tens of thousands of dollars.

Nevertheless, for the needs of geologists and jewelers, simple spectroscopes based on a diffraction grating are produced. Their cost is from 1200 to 2500 rubles. And it's a fun and useful thing.

The spectroscope looks like this:

You need to look into the eyepiece (on the left, where the cone is), while the lens (on the right) should be directed towards the radiation source.

A diffraction grating splits light into a spectrum (like a rainbow or an optical prism).

Before delving into the spectra of real lamps, let me remind you general information. (This is discussed in some detail in the book in the chapter “Quality of Light”).

Here I will show two SDL spectra with an exceptionally high color rendering index of 97:

Cold light:

You can see that the color temperature is 5401 K, index 97. The main thing is that you can see what colors visible to the eye the spectrum consists of.

Warm light:

Temperature 3046 K, index also 97.

A spectrophotometer - unlike a spectroscope - shows not just which colors form the spectrum, but also gives their intensity. It is clearly visible that in the spectra of both lamps there are all the colors that make up white (“every hunter wants to know where the pheasant sits,” i.e. red, orange, yellow, green, blue, indigo, violet). The difference in color temperature is achieved through the relative contributions of cool (blue-cyan) and warm (yellow-red) components.

I am forced to mention that this spectroscope is intended for mobile use using the eyes. It is extremely inconvenient to fix the image, since the eyepiece is small and there are no devices for fixation on the camera. Therefore, you need to hold the camera with one hand, the spectroscope with the other, and control the shooting with your voice. At the same time, you still need to keep the direction towards the light source; small deviations from the normal lead to distortion of the colors of the spectrum. Of the almost dozen different cameras that I have at home, the Samsung tablet turned out to be the best. The camera is only 5 megapixels, but the software is good, and the size and position of the lens on the device body allows you to more or less conveniently attach the spectroscope. The white balance was fixed as “daylight”, ISO 400. The pictures were not processed, only straightened and cropped. The numbers on the right indicate the color rendering index of the source (100 - daylight in cloudy weather, 99 - incandescent lamp). I'm not very happy with the quality of the photos - but I couldn't take it better.

So let's start from top to bottom and specific examples Let's try to understand what you need to pay attention to in such spectra.

Daylight and incandescent: an ideal spectrum that includes all of the above colors.

SDLs with color rendering indices of 87 and 84 also demonstrate almost a full range of. The problem is usually the red part - while yellow and orange are usually sufficient, deep red shades are most often absent. They are not visible here either. It can also be assumed (for example, by the amount of blue in the spectra) that manufacturers use different 5736SMD LEDs. Those. We are not dealing with the same lamp purchased from different sellers - but with different manufacturers.

SDL with index 78 (its analysis is given in the chapter “Example of assessment testing” in the book) along with the trimmed red part also shows a small amount of blue. (It may seem that in comparison with the spectrum of a lamp with index 84, this is not the case. But here you need to remember that 84 is a warm lamp, T = 2900. And 78 is cold, T = 5750 K, there is, by definition, much more blue) . This is precisely the main disadvantage of simple budget SDLs, which produce supposedly white light due to the blue or purple radiation of the LED and the yellow-orange light of the phosphor. To the right of blue lies blue - but from the described combination it “does not work.” Therefore, there is usually a dip there in the SDL spectrum. Due to this (plus a deficiency of deep red) the color rendering index drops.

The lowest spectrum is a high-quality compact Fluorescent Lamp(CFL, T=2700 K, resource 12000 hours, declared color rendering index of at least 80). And here you can clearly see how this formally rather high value is achieved. The manufacturer itself calls this the “Tricolor system”. Those. it uses a phosphor of 3 components, each of which emits light in a narrow band. (Of course, it is not at all easy to make such a lamp, since a careful selection of the combination of phosphors is required.) It is the presence of such vertical stripes (for example, violet, green, yellow) that is a sign of low-quality light sources. The second consequence of the line spectrum of the source is the physical absence of some colors in principle (in the figure, for example, there is practically no yellow and very little blue). It is obvious that the light of such lamps is of little use to the eyes, despite the formally quite high performance. Such lamps should be used in lamps with high-quality diffusers (although, of course, this will not change the spectrum of the lamp).

Conclusion: in the spectra of light sources with a high color rendering index, all colors of the spectrum should be present and there should be no intense narrow bands.

Separately, I would like to warn against haste in analyzing the spectra. In my line of work, I talked a lot with spectroscopists and noticed an ironclad pattern: the more qualified and professional the specialist, the more cautious and evasive he is in his conclusions. From the best of them, the professor, head of the spectroscopy laboratory, it was generally impossible to achieve a clear conclusion (which at first, when I was young, irritated me wildly). The eye is undoubtedly the best optical instrument in existence. But the analysis and interpretation of spectra is endless complex topic. There are a huge number of different factors at work. Therefore, I strongly recommend only the simplest qualitative assessment of spectra with the eyes, without attempts at cunning reasoning and far-reaching conclusions. It is best to alternately look at the spectrum of the lamp being evaluated and at the ideal spectrum daylight or LN. Those. clear comparison with each other. published

With the development of LED technology, more and more areas of application are constantly being found for it; it is gradually replacing fluorescent and conventional incandescent lamps. LEDs are much more practical during operation, consume 10 times less electricity, are more durable, and are resistant to mechanical stress. Due to the properties of LEDs to provide radiation in certain spectra of the light range, they began to be actively used for growing plants.

Light spectrum intervals that promote plant growth

It is known that all plants develop through the process of photosynthesis; deeper studies have shown that it occurs more actively in blue and red light. Statistics from various experiments show how some plants differ in the composition of chlorophyll, the intensity of photosynthesis depends on this. Different cultures Depending on the stage of growth, plants absorb a certain part of the light spectrum.

Greens such as onions, parsley, dill grow more actively in the blue spectrum (wavelength 445 nm). At an early stage of development, this range is also preferred by vegetable seedlings. When the period of flowering, ovary and fruit ripening begins, light of the red spectrum in the range of 660 nm is actively absorbed. Some vegetable crops Broad spectrum white light is suitable for favorable growth.

Having studied these properties, you can understand that LEDs are the easiest to adapt to the technology of growing plants in greenhouse conditions under artificial lighting.

Artificial lighting sources

Previously, white LEDs, fluorescent or gas-discharge lamps with a wide spectrum of radiation were actively used for plants in greenhouses. Such lighting is not entirely effective in stimulating plant growth. Much energy is wasted on lighting in the yellow-green range, which is useless for the growth of seedlings.

At the first stage, simple red and blue LEDs were used, LED Strip Light. But these diodes had a fairly wide scattering range beyond the red and blue spectrum, high cost and low illumination intensity. In the process of successive improvements, the LED crystals began to be covered with a layer of phosphor, which has the properties of transmitting only blue and red rays. New phytolamps emit purple light. Technologies using phosphor made it possible to achieve maximum effect in all respects:

low production costs;
maximum concentration of radiation energy in the blue and red ranges;
maximum radiation intensity;
economical mode of electricity consumption.

Such LEDs ensure the active process of photosynthesis, stimulating plant growth. Work to improve the parameters of the emitted spectrum is constantly ongoing; manufacturers are trying to make phytophotodiodes, bringing it as close as possible to the spectrum of sunlight. One of the modern examples is full-spectrum phyto-LEDs Bridgelux 35 mm and Epistar, the first has a more convex diffuser lens.

Appearance Bridgelux 35mm

Technical characteristics of Bridgelux 35 mm:

rated power – 1 W;
voltage from 3.0 to 3.4 V;
current – 350 mA;
full color spectrum for plants 400–840 nm;
service life – 50,000 hours;
beam dispersion direction – 120 degrees;
Dimensions – Ø chip with housing 9 mm, Ø lens 5.6 mm, height of the entire chip structure 6 mm.

The peculiarity of these phyto-LEDs is that they do not require several chips with different emission spectra - blue or red. IN in this case everything is mounted in one chip with a wide spectrum of illumination, where blue and red colors predominate.

Comparative analysis of the spectra of a red LED and a phytophotodiode

The intervals of yellow, green and other spectra are significantly reduced. This allows you to concentrate energy on emitting useful colors.

The main advantages of phytoLEDs

The emission spectrum covers the entire range from 400 to 840 nm.
The distribution of radiation intensity of parts of the spectrum is as close as possible to sunlight.
The problem of using several types of LEDs with different spectra is solved when red and blue LEDs are inserted into the lamp.
Phyto-LED effectively stimulates plant growth throughout the entire development period: before flowering, during flowering, fruit set and ripening. No need to change light sources at different stages. The phytophotodiode is assembled on the basis of a single crystal.

Lamps with phyto-LED elements, which have a full spectrum of sunlight, work 1.9 times more efficiently than simple phytolamps with peaks in the red and blue range. And 1.2 times better than assemblies using individual diodes of different spectrums.

An example of a design for illuminating seedlings with phyto-LEDs

It has been noticed that under phytolamps of the red and blue spectrum the sprouts grow higher, but there are fewer ovaries on the flowers. Full spectrum phytophotodiodes have less intense blue light than red light. The contrasts of the spectrum are balanced so that LEDs for plants do not provide significant growth in height, but the maximum number of fruits.

The superiority of full-spectrum phytophotodiodes over other models is obvious. In order for them to be used even more widely, it remains to improve the details to increase the intensity of the light flux.

But growing flowers in our winter conditions is not easy. I’ll tell you about what helps in growing plants - special light, phytolamps.

Happy spring holidays, dear ladies! What is a spring holiday without flowers?

About homemade lamps I have already written several articles for plants

Now I’ll tell you about special LEDs for plants with a “full spectrum”
The process is highly dependent on the light spectrum.

Therefore, it is more effective to use light as close as possible to 445nm and 660nm. It is also recommended to add an infrared LED. Quite a few copies have been written about all this on the relevant forums. I won’t theorize, I’ll move on to practice. This time, in the vastness of ALI, I purchased 3-watt “full spectrum” LEDs for plants.

Product characteristics

Power: 3W (there is 1W in the same lot)
Working current: 700mA
Operating voltage: 3.2-3.4V
Chip manufacturer: Epistar Chip
Chip size: 45mil
Spectrum: 400nm-840nm
Certificates: CE, RoHS,
Lifespan: 100,000 hours
Purpose: lamps for plants

The price of LEDs is quite attractive.
The packaging is very simple.

In appearance, the LED is similar to its cold and warm white brothers.

The packaging was left over from previously used LEDs.

LED testing

To begin with, check the power and take the current-voltage characteristic
Computer power supply, used by me as a laboratory one and the good old PEVR-25, personifying a great era)))

Measuring current/voltage with a simple device, since special accuracy is not required here. Well, and a heatsink, so as not to overheat the LED while I’m mocking it. Additionally, I measured the illumination in each mode at a distance of approximately 15-20 cm to assess the effectiveness of the glow at different currents.

I increased the LED power to 7.5W, I thought he would die, but no, he survived!

Let's see what the graph of voltage and illumination versus current gives.

The voltage changes fairly linearly. There are no signs of crystal degradation at a current of 1.5A. Everything becomes more interesting with lighting. After approximately 500mA, the dependence of illumination on current decreases. I conclude that 500-600mA is the most effective mode of operation with this LED, although it will work quite well at its rated 700mA.

Spectral analysis

I used a spectroscope for spectral analysis

We shine light into one tube with the source being studied, and into the other, we illuminate the scale. We look at the finished spectrum through the eyepiece

Unfortunately, this spectroscope does not have a special attachment for photography. The picture was visually very beautiful and did not want to be produced on a computer. I tried different cameras, phones and tablets. As a result, I settled on , with the help of which I somehow managed to take pictures of the spectrum. I completed the scale numbers in the editor, since the camera did not want to focus normally.

This is what I ended up with
Solar spectrum

Fluorescent table lamp
The spectral lines of mercury are clearly visible

As a radiator I use a U-shaped 30mm aluminum profile. There are 10 LEDs on 1m of profile (about 20W). During continuous operation, such a lamp heats up to no more than 45C.

I make driver housings from electrical cable channel.

To glue the LEDs to the profile I use Kazan sealant, although hot-melt adhesive would also work.

Then I connect everything with wires, I insulate the contacts with heat shrink

Now the driver and phytolamp are ready

A couple of hours of running shows that the thermal calculation was done correctly and there will be no overheating even during long-term operation

The light from the lamp is softer than that of separate 440nm and 660nm LEDs. It is less blinding to the eyes.

It's time to take stock

LEDs with “full spectrum” fully justify their purpose and are suitable for making phytolamps.

The declared power and spectrum correspond to the declared characteristics, although the infrared component could not be verified.

The required spectrum in such LEDs is achieved using a special phosphor, so the design of the diodes themselves can be anything. You can take powerful matrices of 20W and higher for use in greenhouses. For illuminating seedlings and indoor plants These LEDs are quite enough.

Exit inspection passed!

Nevertheless, for the needs of geologists and jewelers, simple spectroscopes based on a diffraction grating are produced. Their cost is from 1200 to 2500 rubles. And it's a fun and useful thing.

The spectroscope looks like this:

You need to look into the eyepiece (on the left, where the cone is), while the lens (on the right) should be directed towards the radiation source.

A diffraction grating splits light into a spectrum (like a rainbow or an optical prism).

Before delving into the spectra of real lamps, let me remind you of some general information. (This is discussed in some detail in the book in the chapter “Quality of Light”).

Here I will show two SDL spectra with an exceptionally high color rendering index of 97 (source):

Cold light:

You can see that the color temperature is 5401 K, index 97. The main thing is that you can see what colors visible to the eye the spectrum consists of.

Warm light:

Temperature 3046 K, index also 97.

So, let's start from top to bottom and use specific examples to try to understand what you need to pay attention to in such spectra.

Daylight and incandescent: an ideal spectrum that includes all of the above colors.

SDLs with color rendering indices of 87 (review) and 84 (discussed at the manufacturer's choice) also demonstrate almost the full spectrum. The problem is usually the red part - while yellow and orange are usually sufficient, deep red shades are most often absent. They are not visible here either. It can also be assumed (for example, by the amount of blue in the spectra) that manufacturers use different 5736SMD LEDs. Those. We are not dealing with the same lamp purchased from different sellers - but with different manufacturers.

The lowest spectrum is a high-quality compact fluorescent lamp (CFL, T=2700 K, resource 12,000 hours, declared color rendering index of at least 80). And here you can clearly see how this formally rather high value is achieved. The manufacturer itself calls this the “Tricolor system”. Those. it uses a phosphor of 3 components, each of which emits light in a narrow band. (Of course, it is not at all easy to make such a lamp, since a careful selection of the combination of phosphors is required.) It is the presence of such vertical stripes (for example, violet, green, yellow) that is a sign of low-quality light sources. The second consequence of the line spectrum of the source is the physical absence of some colors in principle (in the figure, for example, there is practically no yellow and very little blue). It is obvious that the light of such lamps is of little use to the eyes, despite the formally quite high performance. Such lamps should be used in lamps with high-quality diffusers (although, of course, this will not change the spectrum of the lamp).

Conclusion: in the spectra of light sources with a high color rendering index, all colors of the spectrum should be present and there should be no intense narrow bands.

Separately, I would like to warn against haste in analyzing the spectra. In my line of work, I talked a lot with spectroscopists and noticed an ironclad pattern: the more qualified and professional the specialist, the more cautious and evasive he is in his conclusions. From the best of them, the professor, head of the spectroscopy laboratory, it was generally impossible to achieve a clear conclusion (which at first, when I was young, irritated me wildly). The eye is undoubtedly the best optical instrument in existence. But the analysis and interpretation of spectra is an endlessly complex topic. There are a huge number of different factors at work. Therefore, I strongly recommend only the simplest qualitative assessment of spectra with the eyes, without attempts at cunning reasoning and far-reaching conclusions. It is best to alternately look at the spectrum of the lamp being evaluated and at the ideal spectrum of daylight or FL. Those. clear comparison with each other.