LED lighting – nuances

Recommendation points

• Less electricity costs – more light
• How long will the LED lamp last
• Types of LED lamps
• LED lamp selection

In this article, we will talk in detail about LED lighting, because in the coming years, these lamps will be installed in most lamps inside and near our homes. You will find out what types of LED lamps exist, on what factors the service life of an LED lamp depends, how to make the right choice.

Compared to the usual household lamps – with a filament and fluorescent – most of us know very little about LED electrical equipment. No, ordinary LEDs have been present in everyday life for a long time, informing us about the switching on of household appliances or sparkling with multi-colored lights on the New Year tree, but how can they illuminate a room or street – LEDs are so small, aren’t they? I propose to closely examine LED lighting from all sides, because in the coming years these lamps will be installed in most lamps inside and near our homes.

Less electricity costs – more light

Any electric lamps convert the electricity received to them into light radiation, visible to the human eye and measured in lumens. The higher the luminous efficacy, the more efficient these luminaires are..

Let’s compare LED lamps and “Ilyich lamps”. Two decades earlier, to improve illumination, households replaced, for example, a 100-watt incandescent lamp with a more powerful 150-200 watt lamp, or installed lamps with several sockets, in any case increasing electricity consumption. The ratio between the consumed electricity and the luminous efficacy of incandescent lamps is – 1 watt, about 12 lumens. It is possible to increase the luminous efficiency of such lamps only by increasing the heating temperature of the tungsten filament, but this will seriously lower their already short service life – an ordinary 100 W lamp cannot shine for more than 1000 hours, since heating destroys the incandescent filament. The only way to increase the service life is to reduce the already low efficiency, which does not exceed 15%. For example, lowering the efficiency value to 4% by reducing the voltage consumed by the lamp, you can increase its service life a thousandfold – but such a lamp will shine completely dim.

Modern LED lamps for each consumed watt of electricity produce at least 100 lumens, the intensity of the luminous flux they generate exceeds that of incandescent lamps by about 10 times. For example, LED floodlights are more efficient and less energy intensive than their incandescent counterparts. The luminous efficiency of an LED lamp depends on the type and temperature of LED heating, the characteristics of the power supply, as well as on its design – optical and light-scattering elements located on the lamp base.

To achieve maximum light output, equipping a lamp with only high quality LEDs is not enough. The manufacturer must build the most effective thermal regime inside it – if the temperature of the LEDs in the active region (the electron recombination zone on the crystal surface) increases by 10 ° C, then the luminous flux of such a lamp will decrease by 2.5%. In other words, an LED lamp that generates a luminous flux of 100 lumens, with heating in the electron recombination zone of about 25 ° C, after installation in a closed lamp can heat up in the active zone to 100 ° C – the intensity of its light radiation in this case will decrease to 80 lumens.

Directivity of light radiation. Incandescent and fluorescent lamps, being installed in luminaires, generate a uniform luminous flux in all directions – such lighting can be focused in one direction only with the help of a lampshade or reflector. The light emission of LEDs is always directed only in one direction, therefore, LED lamps are equipped with an optical element (secondary optics) that changes the linear direction of the luminous flux from each LED to the required angle, which allows you to obtain some light scattering.

The linearity of the luminous flux produced by an LED lamp is both an advantage and a disadvantage of lamps of this type – on the one hand, the lumens are not wasted and illuminate only the necessary areas, which allows installing lower power lamps in the lamps. On the other hand, the construction of lighting with LED lamps must be taken especially responsibly, because incorrect placement of lighting devices will lead to the formation of overly illuminated and too dark areas in the room..

How long will the LED lamp last

Various manufacturers talk about a service life of 30,000-100,000 hours, that is, in the first case, the lamp will last more than 8 years, in the second – over 27 years, provided that the lamp is used daily for 10 hours. As mentioned above, the service life of LED lamps depends on similar characteristics of the LED – let’s take a closer look at them..

The first criterion affecting the life of a LED is the quality of the LED crystal and the uniformity of its structure. During operation, the crystal degrades for two reasons – as a result of multiple violations of the crystal lattice and due to the migration of metal atoms forming the electrodes.

a) construction of a conventional LED: 1 – anode; 2 – cathode; 3 – conductor; 4 – crystal; 5 – plastic lens
b) construction of a powerful LED: 1 – body; 2 – conductor; 3 – heat sink; 4 – crystal; 5 – lens; 6 – cathode

In those areas of the crystal where the crystal lattice has suffered the most damage, electricity is consumed only with the release of heat, that is, without light radiation. The exact cause of this defect has not been established, but static electricity is believed to be causing it..

Metal atoms penetrating into the crystal structure from the electrodes cause leakage currents – the movement of current in the crystal through metal inclusions at the atomic level, no light is produced. With an increase in the current and temperature, the process of penetration of metal atoms into the crystal of the LED increases sharply, while the light radiation and voltage fall – such an LED will quickly fail. This disadvantage is inherent in inexpensive “overclocked” LED lamps, which have a high brightness with insufficiently efficient heat dissipation – unscrupulous manufacturers prefer this, the cheapest way to increase the light performance of their products due to the relatively short service life of the product.

However, not only the manufacturer, but also the user is often to blame for the rise in temperature inside the LED lamp and, as a result, rapid wear. A radiator that removes heat from the LEDs must release it to the surrounding air or to the wall to which the luminaire is attached. If you install several LED lamps in a suspended ceiling or close their bulb with a closely adjacent material, then even the highest quality lamp will quickly overheat due to lack of space for heat dissipation. By the way, it will be correct to install Armstrong LED ceiling lamps in the false ceiling, made in the form of panels.

Poor heat dissipation during operation of the LED lamp also affects the phosphor covering the LED crystal and the optical system built into the LED. A sign of wear of the phosphor is a bluish tint of light radiation caused by the predominance of direct radiation from the crystal. The optical system, made mainly of silicone or plastic, loses its transparency, which reduces the light output of the LEDs.

It should be noted that LEDs from four of the world’s largest manufacturers in this area, namely the Japanese company Nichia, the Dutch Philips, the American Gree and the German Osram, have the highest performance and longest life. With regard to the service life of LED lamps, it should be noted that they can generate light radiation for several decades, but the intensity of this radiation will gradually decrease for the reasons described above. After 25,000 hours (when working 10 hours a day – 6.5 years) of operation, the luminous flux intensity will decrease by 25-30%, which, however, meets the requirements of modern standards.

Types of LED lamps

Depending on their purpose, LED lamps are divided into street, industrial and household.

LED outdoor luminaires emitting white light are designed to illuminate roads, parks and various architectural structures; they do not have a replaceable lamp. Their housing serves two purposes – to provide maximum protection against dust and moisture, and also to act as a radiator that removes heat into the atmosphere..

Luminaires for offices (white light), housing and communal facilities and industrial workshops also do not have any replaceable elements and practically do not need maintenance. They differ from street luminaires in that they meet more stringent requirements for lighting quality, stable color rendering and operating conditions..

Household LED lamps (yellow light) have a low power (up to 20 W), their design and characteristics meet a number of requirements for the quality of lighting, fire and electrical safety, they have a decorative appearance. Typically, household luminaires are equipped with replaceable LED bulbs. This group of lamps is the most diverse in its design and installation location – they can be embedded in the ceiling, floor, walls, furniture, suspended, used for table lighting, as a night light, spot lighting, etc..

LED lamp selection

The life of an LED lamp depends on a number of characteristics incorporated into it during production, therefore the name of the manufacturer is important when choosing – that is, only the price criterion does not determine its quality. Let’s move on to the choice – how not to make mistakes by purchasing a not cheap LED lamp at all?

The usual selection criterion – the power of the lamp in watts – is not entirely indicative in relation to LED lamps, since it only reports its energy consumption per unit, and we need to know the amount of light radiation.

Light emission, measured in lumens (lm), characterizes the ability of a given lamp to illuminate a room. In some cases, the manufacturer “forgets” to indicate the value of the luminous flux on the packaging of the lamp, citing only a comparison with an incandescent lamp of a certain power – they say, this LED lamp fully corresponds to it in terms of lighting quality. I suggest using the table below to determine the relationship between light emission and lamp power..

Incandescent lamp power (W)	Fluorescent lamp, power (W)	LED lamp, power (W)	Luminous flux (lm), average
20	5-7	2-3	250
40	10-13	4-5	400
60	15-16	8-10	700
75	18–20	10-12	900
one hundred	25-30	12-15	1200
150	40-50	18–20	1800
200	60-80	25-30	2500

It would seem that these data are enough to make the choice of an LED lamp, but this is not so – it should be taken into account that LED lamps emit a narrow beam, in contrast to fluorescent and incandescent lamps. Manufacturers expand the angle of illumination of the lamp with an optical element, indicating the angle of divergence of the light beam on the package. If the angle is 120 °, then this means the following – the luminous flux emitted by the lamp decreases by half as the light flux deviates from the central axis by 60 °. The directivity pattern of light radiation with a divergence of 120 ° is quite wide – the space under such a lamp will be illuminated over a large area with almost the same brightness. LED lamps with an angle of divergence from 20 ° to 30 ° are suitable only for area (accent) lighting, they are not suitable for ordinary room lighting.

Great, you might think, you should choose LED lamps with 120 ° divergence – no matter how it is! Wide angle lighting creates another problem – high brightness at wide angle, which can cause discomfort to the eyes of households. For this reason, lamps with a wide spreading angle can only be installed in ceiling and wall luminaires that meet the requirement for a protective angle. Let me explain: the protective angle of the luminaire is the largest angle at which the light source (lamp) itself does not fall into the direct line of sight of the human eye, that is, it does not light up the eyes. The protective angle in the luminaires is created with the help of lattice screens, set at a certain distance from the lamp bulb.

The next indicator is the color temperature, or, in other words, the color tone of the light radiation generated by a given lamp. If everything was simple with incandescent lamps – their light was only yellow, then in the case of fluorescent and LED lamps this is not the case. When choosing a lamp, be sure to pay attention to the color temperature indicated on the package in degrees Kelvin:

• From 2700 to 3500 ° K – the so-called “warm” light with a yellow tint, similar to the light radiation from incandescent lamps. At the same time, lamps with a color temperature of 2700 ° K emit a pronounced yellow light, but their luminous flux is not so strong, and those with a color temperature of 3500 ° K are distinguished by more powerful light radiation with lower shades of yellow (they produce more white light than yellow).
• From 4000 to 5000 ° K – neutral white light emission, providing bright illumination. These lamps are commonly used in offices, businesses and public institutions;
• More than 6500 ° K – cool white light with high luminous efficacy. This group of lamps is only used for street lighting.

Finally, be sure to pay attention to the color rendering index (color rendering index) indicated on the lamp packaging – its numerical value characterizes how much the color of objects illuminated by this lamp will match their natural color. The optimal value of this indicator will be a color rendering index of 70 and above (or a color rendering degree of at least 2A). Street lamps may have a lower index value of 60 (or 2B), but not lower.