Technical Information — Lighting

LED Technology: How It Works, Light Metrics and Efficiency

The light-emitting diode (LED) has largely replaced classic light sources — at far lower energy consumption and with a long service life. This article explains the semiconductor principle, the key lighting metrics and socket compatibility.

What is an LED?

An LED (Light Emitting Diode) is an electronic semiconductor component from the diode family. It has a p-n junction and emits light of a specific wavelength when current flows in the forward direction — depending on the semiconductor material used.

The first lecture on current conduction through crystals was given by Ferdinand Braun back in 1876: he pressed a metal tip onto a sulphur crystal, which conducted current well in one direction and poorly in the other. This rectifying effect did not fit the laws known at the time — it took almost 60 years to explain it physically.

Operating principle of an LED: p-n junction with recombination

How does an LED work?

The starting point is a pure semiconductor crystal with equal numbers of free electrons and electron holes. Targeted doping (adding foreign atoms) increases the number of free charge carriers:

n-type (electron surplus)
Adding pentavalent foreign atoms (donors, e.g. phosphorus) — they donate an extra electron.

p-type (electron deficiency)
Adding trivalent foreign atoms (acceptors, e.g. boron) — electron holes are created.

When the n- and p-layers are joined and a forward voltage is applied, electrons move through the p-n junction and recombine with the holes. The energy released in this process is emitted as light.

LED in Comparison: Lumens Instead of Watts

Brightness is described not by power consumption (watts) but by luminous flux (lumens). The following reference values apply to high-quality LEDs — quality and origin make a clear difference:

Incandescent	Light output	LED
15 W	approx. 100 lumens	1–2 W
25 W	approx. 200 lumens	3–4 W
40 W	approx. 400 lumens	5–6 W
60 W	approx. 700 lumens	7–8 W
75 W	approx. 900 lumens	9–10 W
100 W	approx. 1400 lumens	11–13 W

Lighting Metrics at a Glance

Luminous flux — lumen [lm]	Total light power emitted by a light source.
Luminous intensity — candela [cd]	Luminous flux emitted into a given solid angle.
Illuminance — lux [lx]	Light falling onto a surface.
Light colour — kelvin [K]	Colour temperature: low value = warm, high value = cool.
Energy efficiency	New EU scale A–G since 2021 (replaces the former A++ to E scale).
Switching endurance	Number of switching cycles a lamp can withstand.
Start-up behaviour	Time to reach full brightness (virtually instant for LEDs).

Luminous flux in lumens

Luminous intensity in candela

Choosing the Right Light Colour (Colour Temperature)

Light colour is given in kelvin — the lower the value, the warmer the light:

Warm white — 1500–3000 K
Living and lounge areas, cosy atmosphere.

Neutral white — 3000–5000 K
Offices and workplaces, functional lighting.

Daylight white — from 5000 K
Factory and hall lighting, high concentration.

Scale of light colours from warm white to daylight white in kelvin

Socket Compatibility

Many LED light sources are available as retrofits with common sockets: E27 (standard socket for 230 V incandescent lamps) and E14 (formerly standard up to 40 W). If the socket does not match, a socket adapter can often be used (e.g. G24 → E27). When switching from incandescent lamps to LED, a 2700 K version gives comparably warm light.

LED light sources in the B2B shop

From retrofit lamps to LED strips — a wide selection for industry, trade and public institutions. Need advice? We are happy to help.

» LED lamps · LED strips · Light sources · Advice: +49 (0)7666 / 88499-0 · sales@industry-electronics.com