LDR
Light-dependent resistor
A light-dependent resistor changes resistance according to illumination.
SLD / Schematic
IEC · PE
Photoelectric light switch plan mark
Plan mark for a light-sensitive switch that turns external or perimeter lighting on at dusk and off at dawn.
In plain English
What does Photoelectric light switch plan mark mean?
A photoelectric switch, or photocell, measures ambient light and operates a lighting circuit at a set lux threshold. Plans draw a small switch or box with inward arrows to indicate light received, placed where the cell can see the sky without seeing the luminaires it controls.
A simple example
Photocells are often combined with time switches so that lighting comes on at dusk but goes off at a fixed time. The plan and schedule should show both devices and their logic.
What the drawings help you do
The mark does not give the threshold, time delay or contactor rating. Large lighting loads are usually switched by a contactor operated by the cell.
This particular reference
Plan mark for a light-sensitive switch that turns external or perimeter lighting on at dusk and off at dawn. A light-dependent resistor is a component; a photoelectric switch is a complete lighting control device on the plan.
- Normally open / normally closed
- The contact state in the normal condition defined for the drawing.
- Coil
- A wound conductor that can produce a magnetic field when energised.
- Signal
- Electrical information passed between devices, rather than necessarily the main power supply.
Read the source: IEC graphical symbols for diagrams · Autodesk IEC-60617 preview: Radiation qualifiers
IEC · Light-sensitive switch
IEC 60617 installation-plan style (architectural and topographical installation symbols); independently drawn, not certified IEC geometry or a database identifier.
Shown as an independently authored educational illustration. Use the cited publication and drawing legend to verify the required drafting form.
GA · PE
What it represents
A photoelectric switch, or photocell, measures ambient light and operates a lighting circuit at a set lux threshold. Plans draw a small switch or box with inward arrows to indicate light received, placed where the cell can see the sky without seeing the luminaires it controls.
Photocells are often combined with time switches so that lighting comes on at dusk but goes off at a fixed time. The plan and schedule should show both devices and their logic.
The mark does not give the threshold, time delay or contactor rating. Large lighting loads are usually switched by a contactor operated by the cell.
How to read it
- Check the cell location for a clear view of daylight.
- Look for a contactor or time switch in the same control scheme.
Information to show or reference
- State lux setting range.
- Show associated contactor or time switch.
- Orient the cell away from controlled luminaires.
A distinction that matters
A light-dependent resistor is a component; a photoelectric switch is a complete lighting control device on the plan.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
IEC graphical symbols for diagrams
IEC graphical symbol context; independently drawn here.
Autodesk IEC-60617 preview: Radiation qualifiers
Public IEC-oriented radiation qualifier family for the received-light arrows.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
Explore related references
Put the reference into a drawing workflow.
Elora Grid helps electrical teams work with drawings, specifications and equipment information. Explore the drafting workflow or join the early-access waitlist.