The LED symbol is the diode symbol with two small arrows added. On a dense diagram those arrows are easy to miss entirely.
Look for two small parallel arrows beside the triangle. Pointing away means light leaves the component, so it is an LED. No arrows means a plain diode. Arrows pointing towards the triangle mean something different again — a photodiode, which detects light rather than emitting it.
The LED symbol is the diode symbol with two small arrows added; without them the two are identical.
Drawn from the visual attributes recorded for each symbol. Only traits the two records disagree about are listed.
| Trait | Diode symbol | LED symbol |
|---|---|---|
| Built from | triangles, lines and dots | triangles, arrows, lines and dots |
| Symmetry | horizontal | none |
| Diode symbol | LED symbol | |
|---|---|---|
| What it does | Passes current one way, blocks the other | Does the same, and emits light doing it |
| How to tell them apart | Triangle and bar, nothing else | Triangle and bar plus two arrows pointing away |
| Arrow direction matters | No arrows to read | Away means emitting; toward means a photodiode instead |
| Practical consequence | Fitting an LED here wastes its output or destroys it | Needs a current-limiting resistor a plain diode may not |
| Relationship (from Symbolwise's records) | Commonly confused with LED symbol — The LED symbol is the diode symbol with two small arrows added; without them the two are identical. | Commonly confused with Diode symbol — Identical but for the two added arrows, which are easy to overlook on a dense diagram. |
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for what the component is, how its symbol is conventionally drawn, and where the ANSI and IEC conventions differ. Not used for any claim about the text of IEC 60617, which is paywalled and was not consulted.
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for what the component is, how its symbol is conventionally drawn, and where the ANSI and IEC conventions differ. Not used for any claim about the text of IEC 60617, which is paywalled and was not consulted.
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for what the component is, how its symbol is conventionally drawn, and where the ANSI and IEC conventions differ. Not used for any claim about the text of IEC 60617, which is paywalled and was not consulted.
Alpha is a Greek letter and stands for a quantity — an angle, a coefficient, a significance level. The proportionality sign is an operator and stands between two quantities to say they keep a constant ratio. The drawings differ in that the proportionality sign's right-hand stroke runs out in an open curve rather than closing into the letter's tail.
Look at the left-hand edge. A straight flat back is an AND gate: the output is true only when every input is. A curved concave back is an OR gate: true when any input is. Everything else about the shapes is similar, which is why the back edge is worth checking deliberately rather than at a glance.
Equal-length lines mean a capacitor. Alternating long and short lines mean a battery, with the long line positive. If the second line is curved rather than straight it is a polarised capacitor — still a capacitor, but one that must be fitted the right way round.
Look at the pattern. Even short dashes throughout is a hidden line: an edge that exists but is concealed behind material. Long dashes alternating with dots is a centre line: an axis of symmetry or the centre of a circle, which is not a physical edge at all. Reading a centre line as an edge is the commonest beginner's error on a drawing.