Motion sensor lights are a great way to keep yourself safe and secure in your home.
But do they work through glass?
Motion sensor light bulbs don’t detect any motion beyond glass. These devices use passive infrared energy. A glass barrier absorbs infrared energy, so the bulbs won’t detect any heat changes, preventing them from detecting motion.
The rest of this article will discuss why motion sensor light bulbs don’t work through glass, which motion sensor bulb works best for this use case, and other types of motion sensors to consider.
Why Motion Sensor Light Bulbs Don’t Work Through Glass
To understand why your motion sensor light bulbs won’t detect any movement beyond glass obstacles, you need to have a basic sense of how these sensors work.
Motion sensor light bulbs use PIR technology.
They typically feature two pyroelectric sensors positioned at an angle to each other.
Passive infrared radiation (PIR) is a type of radiation with wavelengths from 0.7 to 1 millimeters.
When a human being enters the detection zone of a PIR sensor, it detects infrared energy and triggers the lights.
However, if that person stands behind a pane of glass, then no infrared energy will reach one sensor and set off the motion sensor light bulb.
In simple terms, infrared means the type of energy invisible to the human eye.
However, humans detect this energy in the form of heat, which is why most motion sensor light bulbs are equipped with infrared emitters.
However, when there’s a glass barrier between the sensor and object, the glass absorbs all of the heat.
Therefore, the sensors can’t detect movement beyond the glass because there’s no heat.
Other types of motion sensors that use PIR technology suffer from the same shortcoming.
Here’s a video that describes how these sensors work:
Which Motion Sensor Bulb Works Through Glass?
In general, a radar motion sensor bulb works through glass. These bulbs use photocell sensors that detect infrared and visible light. Since light travels through glass, this type of bulb can detect movement beyond the glass.
Typically, when the bulb picks a change in the visible spectrum, it has detected motion.
And since glass doesn’t absorb this part of the light spectrum, you can get motion detection beyond any glass obstacle.
Other Motion Sensors To Consider
So far, I’ve only discussed PIR and photocell technologies, but there are other types of motion sensors to consider. Here’s a rundown of these alternatives and their pros and cons:
Microwave Sensors
These sensors use microwave technology rather than infrared or visible light.
They can detect movement beyond glass because microwaves are reflected off of the person or object, even when they’re behind glass.
Microwave sensors are expensive and often require professional installation due to their height requirement.
They also have a limited range of 40 feet (12.19 m) or less, so you’ll need more than one for most homes.
Pros
- Detect movement beyond glass and through other objects.
Cons
- Require professional installation due to height requirement.
- Only detect smaller objects within a limited range (40 feet or 12.19 m or less).
Optical Sensors
Optical sensors work just like photocell sensors, but they emit infrared light as opposed to visible light.
When the light source detects a change in the infrared spectrum, it has detected motion.
As with microwave sensors, optical sensors are often used for security purposes to keep unauthorized people out of restricted areas because they don’t penetrate through glass or other solid objects.
Pros
- Provide a high resolution.
Cons
- Don’t work through glass.
- May require professional installation.
- Have a limited range (about 15ft or 4.57 m).
Ultrasonic Sensors
Ultrasonic motion sensors emit ultrasound waves and detect changes in reflections from people or objects, even through glass.
Ultrasonic sensors are used in home automation for things like controlling lights or appliances.
They’re also common in garage door openers and some security systems.
These sensors emit high-frequency sounds that humans can’t hear, but they do pass through glass.
The sound waves bounce back when they get to the other side of the pane of glass, and the sensor detects the change in reflection.
This type of system is simple and very effective, but it doesn’t work well in loud or high-traffic areas due to echoes or multipath interference.
Pros
- Detect movements beyond glass accurately.
Cons
- Can’t differentiate between moving objects and stationary ones.
- Multi-path interference can interfere with accuracy in loud or hectic locations.
- Require professional installation.
- Have a limited range (around 33ft or 10.05 m).
Reflective Motion Sensors
These devices use infrared sensors to detect changes in the reflective surfaces people or objects leave behind.
The reflective sensors don’t emit any waves themselves.
They rely entirely on what you have in your homes, such as walls, floors, ceilings, mirrors, appliances, and furniture.
If anything moves in the space where you use these sensors, the infrared beam is broken and triggers a response.
Pros
- Can detect both stationary and moving objects.
Cons
- Don’t work through glass.
Frequently Asked Questions
Will Motion Sensors Work With LED Lights?
Motion sensors work with LED lights in the same way they do with incandescent lights. Therefore, you won’t need additional wiring or rewiring when swapping out an incandescent light for an LED light.
However, the LED light must be compatible with the motion sensor. If you’re using a motion-sensing light bulb, check the package to make sure it includes an LED light.
Do You Need Special Bulbs for Motion Lights?
You don’t need special bulbs for motion lights. Standard LED, and CFL downlight bulbs will work great in your home. Just make sure they’re compatible with your motion sensor.
To check for compatibility, read your motion lights’ technical specifications (usually included in its product details which you’ll find on its box or online). If you don’t find this information, I recommend calling the manufacturer.
Do Motion Sensor Lights Deter Burglars?
Motion sensor lights are good for deterring burglars. When these bulbs light up, they let your neighbors and others nearby know there’s activity on your property and may draw attention to the area.
This could work to your advantage, as burglars are less likely to break into a home where there’s surveillance.
That said, here are other effective ways to burglar-proof your home:
- Install a home security system (like this SimpliSafe Home Security System from Amazon.com.
- It comes with 24/7 professional monitoring and an alert feature that automatically contacts the police and the medical dispatch in case of an emergency).
- Install window locks.
- Install a burglar alarm on your doors and windows.
- Secure vulnerable entries to your home, such as garage doors and skylights.
The Bottom Line
So, do motion sensor light bulbs work through glass? Unfortunately, no.
These sensors use PIR technology which detects object heat-maps. Since glass absorbs infrared energy, these gadgets can’t detect movement beyond it.
However, there are a few alternative sensors that work beyond glass obstacles.
Examples include radar sensors, which use photocells to detect visible and infrared light, or microwave sensors, which use microwaves to detect movement. Each product comes with its own set of pros and cons.
