LED explained: how modern light sources work
Within two decades the light-emitting diode has replaced the bulb that lit our homes for more than a century. What an LED is, how it makes white light and what separates good from mediocre.
For more than a century, artificial light meant heat: first a flame, then a glowing wire. The light-emitting diode, or LED, works on an entirely different principle, closer to a computer chip than to a candle. Within roughly two decades it has become the standard light source in homes, gardens and museums, and it has changed what lamps can look like.
What a light-emitting diode is
An LED is a tiny piece of , a crystalline material that conducts electricity only under certain conditions. It is made of two layers, one with a surplus of electrons and one with a shortage. When current flows, electrons cross the boundary between the layers and drop into a lower energy state, releasing the difference as a small packet of light.
The colour of that light depends on the material. Red LEDs appeared in the 1960s, at first as small indicator lights, and other colours followed. Efficient blue LEDs arrived only in the early 1990s, an achievement honoured with the Nobel Prize in Physics in 2014 for Isamu Akasaki, Hiroshi Amano and Shuji Nakamura. Blue was the missing piece, because it made bright, efficient white light possible.
How white light is made
Most white LEDs start with a blue chip coated in a , a fine yellowish layer. The phosphor absorbs part of the blue light and re-emits it as a broad band of green, yellow and red. The remaining blue and the converted light mix into white.
The recipe of the phosphor decides the character of the light. More red produces a warmer colour temperature and better colour rendering, at the cost of a little efficiency. This is why high-quality warm white LEDs with a colour rendering index of 90 or more are slightly less efficient than basic cool white ones. Some specialist LEDs start from a violet chip instead of a blue one to render colours even more fully.
Efficiency, heat and lifetime
| Property | Incandescent bulb | LED lamp |
|---|---|---|
| Efficacy (lumens per watt) | about 10 to 17 | often 100 or more, the best above 200 |
| Power for about 806 lumens | 60 W | about 4 to 9 W |
| Typical rated life | about 1,000 hours | about 10,000 to 50,000 hours |
| How it ends | The filament breaks suddenly | Light fades gradually, or the driver fails |
| Heat | Hot bulb, much infrared in the beam | Little heat in the beam, heat must escape at the back |
Typical ranges. Real life depends heavily on operating temperature and the quality of the electronics.
An LED turns far more of its electricity into light than a filament ever did, but it is not cold. The heat simply travels the other way: not forward with the light, but backwards into the base of the chip. If that heat cannot escape, the LED loses brightness, its colour drifts and its life shortens. Good lamps and fittings therefore use aluminium bodies or fins as a .
Unlike a bulb, an LED rarely dies with a pop. Its output slowly declines, and lifetime is usually stated as the number of hours until it falls to a set share of the original light, often 70 percent, written . In practice the , the small electronic power supply that feeds the LED, is often the part that fails first.
Retrofit lamps or integrated LED
There are two ways to bring LED into a lamp. lamps imitate the old bulbs, with familiar caps such as E27, E14, GU10 or G9, and fit existing lamps. They are ideal for classic designs and antiques, and decorative filament versions recreate the look of the earliest carbon filament bulbs.
Integrated fittings build the LED directly into the luminaire, often as a flat module with its own driver. This allows forms that were impossible with bulbs: razor-thin pendants, glowing rings, light hidden in a shelf. The question to ask is whether the LED module and the driver can be replaced when they eventually fail. Careful manufacturers design for this and keep spare parts; a fitting with the LED glued in permanently may become waste when one small part gives up.
Why quality differs so much
Two LED lamps with the same lumens and colour temperature can look and behave very differently. The differences lie in details that rarely appear on the front of the box.
- Colour rendering: CRI 90 or more for living spaces, with a good R9 value for reds.
- Colour consistency: measured in SDCM or MacAdam steps; three steps or fewer means lamps of the same type match closely.
- Flicker: basic drivers can produce flicker that is barely visible but that some people find uncomfortable, and it shows as stripes on a phone camera.
- Dimming: smooth dimming down to low levels without buzzing requires a well-designed driver.
- Heat management: a solid metal heat sink generally signals a longer life than a light plastic body.
The end of incandescent and halogen
The European Union began phasing out conventional incandescent bulbs in 2009, starting with the most powerful types and moving step by step to lower wattages. Most mains-voltage halogen bulbs followed from 2018, and later ecodesign rules in the early 2020s removed most remaining halogen types and many fluorescent lamps. The bans covered new products rather than existing stock, which is why old types lingered on shelves for a while.
For lamp lovers this matters most with vintage pieces. Almost every classic design can now take a suitable LED, but shape, colour temperature and dimming deserve care, because a lamp designed around a glowing filament reveals a poor light source mercilessly. Rewiring an old lamp is a job for a qualified electrician.
A lamp designed around a glowing filament reveals a poor light source mercilessly.
glaminia is independent and does not sell lamps or recommend dealers. Images are AI generated illustrations, not photographs of specific products. Have fixed electrical work done by a qualified electrician.
