PIR Sensor & Photocell Manufacturer

Engineers working on motion sensor lights, foot lights, and night lights have all encountered similar frustrations: the light triggers falsely during the day when there's plenty of light, or at night when the room has LED lights on, the sensor light still "thinks" it's dark and turns on.

The problem often lies in that tiny phototransistor — what wavelength peak should you choose? What's the significance of the epoxy color? How do you avoid interference from the light's own output?

Today, we'll break down the ins and outs of phototransistor selection for night lights, combining real customer case studies with official NEWOPTO specification parameters.

1. Core Concept: A Phototransistor's "Sensitive Wavelength" Determines What Light It "Sees"

Phototransistors don't respond equally to all light. Their spectral response characteristics determine which wavelengths of light they are more "sensitive" to.

The core function of a night light / sensor light — "turn on when dark, turn off when bright" — essentially relies on the phototransistor detecting ambient light intensity.

But real-world scenarios are more complex than you might think:

• Daytime: Natural light is full spectrum (400~1100nm, including visible + infrared + a small amount of UV), with ample illumination. The phototransistor should be "off" and the light should not turn on.

• Evening / Dark environment: When illuminance drops to a certain threshold (around 10 lux), the phototransistor conducts, and the light enters a trigger-ready state.

• Night with indoor LED lights on: The environment isn't actually dark, but LED white light has a spectrum biased toward blue (peak around 550nm). If the phototransistor isn't sensitive to this wavelength band, it will "mistake" it for nighttime, causing false triggering.

This is the root cause of the problem many customers face — "the sensor light stays on even when the room lights are on."

2. Epoxy Color Isn't Just for Looks — Black, Blue, and Clear Correspond to Three Spectral Responses

Many engineers notice during material selection that phototransistors come with clear, blue, or black epoxy on top.

This isn't just an appearance difference — it's a spectral filtering choice.

• Black epoxy: 700~1100nm (infrared mainly), peak wavelength 850nm. Only sensitive to infrared light, barely responds to visible light. Suitable for outdoor natural light detection scenarios, but has very low sensitivity under indoor LED white light, easily "unable to tell day from night."

• Blue epoxy: 400~700nm (visible light mainly), peak wavelength 550nm. Sensitive to visible light band, spectral response closely matches the human eye function. Can better recognize LED white light, more accurate light sensing in indoor environments, strong anti-infrared interference capability.

• Clear epoxy: 400~1100nm (full spectrum), depends on specific series. Wide spectral response, receives both visible and infrared light. High sensitivity, but also more susceptible to interference from various light sources — selection should be based on specific model parameters.

Key takeaway: For indoor night lights, foot lights, and motion sensor lights, prioritize visible-light-sensitive types (550nm center value, PT-550 series). They recognize LED white light more accurately and effectively reduce false triggering issues.

3. Three Practical Recommendations for Night Light Phototransistor Selection

① Wavelength Selection: Prioritize 550nm Center Value for Indoor LED Environments

Phototransistors with 850nm or 940nm center values mainly respond to infrared bands and work fine in outdoor scenarios dominated by natural light.

But indoor lighting extensively uses LED white light, whose spectral peak is in the visible range with very little infrared component — using infrared-type phototransistors in this situation results in "can't detect light even though the lights are on."

Conclusion:

• ✓ Indoor night lights / sensor lights → choose 550nm visible light center value models

• ✓ Outdoor pure natural light scenarios → consider 850/940nm infrared types

② Avoid Self-Light Interference: Structure + Threshold, Both Matter

A night light emits its own light, which may reflect or refract back through the housing onto the phototransistor, causing flickering or abnormal operation: "light turns on → phototransistor detects light → light turns off → light is gone → light turns on again."

Solutions:

• Structurally: Install the phototransistor in a position that avoids direct and reflected paths from its own light source. Add light-shielding structures if necessary.

• In the circuit: Set the trigger threshold (turn-off lux value) reasonably. The threshold level should be tested and adjusted based on the night light's own light intensity and receiving angle, finding a balance point where "it only turns on when the outside is dark enough, and its own light doesn't affect it."

③ Test with Samples First, Then Finalize for Mass Production

The real performance of a phototransistor is related to PCB layout, housing light transmittance, and installation angle.

We recommend requesting samples during the selection phase, and testing the trigger / off thresholds under different lighting conditions in the finished product environment. Confirm they meet expectations before mass introduction.

4. NEWOPTO Recommended Models and Parameters for Night Light Phototransistors

Model 1: XYC-PT0805BC-L4-D (Blue Epoxy · PT-550 Series)

Core positioning: High-sensitivity visible light type, spectrum matches human eye function, top choice for indoor LED ambient light sensing.

Parameter	Symbol	Test Condition	Min.	Typ.	Max.	Unit
Peak Sensitivity Wavelength	λp			550		nm
Spectral Response Range	λ		400		700	nm
Collector-Emitter Voltage	BVCEO	IC=100μA, Ee=0	30			V
Photocurrent	IL	VCE=5V, 10Lux	2.5		3.6	μA
Dark Current	ID	VCE=5V, 0Lux			0.2	μA
Saturation Voltage	Vce(sat)	IC=2mA, 1mW/cm²			0.2	V
Response Time	tr/tf	VCE=5V, IC=1mA		15		μs
Power Dissipation	PC				70	mW
Operating Temperature	Topr		-30		+85	℃

Product Information:

• Package: 0805 SMD (2.0×1.25×1.05mm)

• Packing: Tape & Reel, 3000pcs/reel

• Features: Blue epoxy filters out infrared, spectral response closest to human eye function, highly accurate light sensing in indoor LED white light environments

• Typical Applications: Night lights, foot lights, motion sensor lights, LCD backlight adjustment, light-controlled toys

Model 2: XYC-PT0805BC-B1-S (Clear Epoxy · PT-550 Series)

Core positioning: Wide-range visible light type, multi-range photocurrent parameters, suitable for light control products requiring precise binning.

Parameter	Symbol	Test Condition	Min.	Typ.	Max.	Unit
Peak Sensitivity Wavelength	λp			550		nm
Spectral Response Range	λ		400		700	nm
Collector-Emitter Voltage	BVCEO	IC=100μA, Ee=0	30			V
Photocurrent	IL(1)	VCE=5V, 10Lux	2	4	6	μA
Photocurrent	IL(2)	VCE=5V, 30Lux	6	12	18	μA
Photocurrent	IL(3)	VCE=5V, 100Lux	20	40	60	μA
Dark Current	Iceo	VCE=5V, 0Lux			0.2	μA
Saturation Voltage	Vce(sat)	IC=2mA, 1mW/cm²			0.4	V
Response Time	tr/tf	VCE=5V, IC=1mA		15		μs
Power Dissipation	PC				70	mW

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Product Information:

• Package: 0805 SMD (2.0×1.25×1.05mm)

• Packing: Tape & Reel, 3000pcs/reel

• Features: Clear epoxy, 550nm visible light peak, provides three photocurrent ranges at 10/30/100Lux for precise binning selection

• Typical Applications: Night lights, light-controlled lighting, light-controlled toys, infrared detection equipment

5. NEWOPTO Phototransistor Product Series Overview

NEWOPTO has focused on R&D and production of photosensitive devices for many years. Our products cover a full range of SMD phototransistors, through-hole phototransistors, photoresistors (CDS), infrared emitters, linear optocouplers, PIR motion sensors, and more, with complete package specifications:

• SMD type: 0603, 0805, 1206, 2835, 3020, 3030, 3528, 3535, 4335, and other packages

• Through-hole type: φ3, φ5, and other specifications

• Wavelength coverage: Visible light type (550nm), infrared type (850nm/940nm), full spectrum type — meeting different scenario requirements

• Customization service: Different sensitivity ranges, angles, shapes, and specifications can be customized according to customer needs

Many customers in the night light / sensor light industry use NEWOPTO photosensitive devices, with full market validation and stable, reliable quality.

6. Why Choose NEWOPTO?

• Deep industry experience, many customers: Most leading customers in the night light / sensor light industry use NEWOPTO photosensitive devices, fully validated by the market

• Complete specifications, flexible customization: Full coverage of visible light, infrared, and full spectrum types; multiple package specifications; customizable sensitivity ranges, angles, and shapes

• Reliable quality, good consistency: Passed multiple reliability tests (solder heat resistance, thermal shock, high temperature & high humidity, life test, etc.), batch consistency is guaranteed

• Strong technical support: Professional FAE team provides selection guidance and application debugging support, helping you avoid detours

• Stocked inventory, stable delivery: Regular models are kept in stock at the factory, small batches can ship quickly

Contact Us

For sample testing, specification requests, or technical selection consultation, welcome to contact the NEWOPTO sales team.

Huizhou NEWOPTO Photoelectric Technology Co., Ltd.
Address: Building 9, Liandong U Valley, No. 252 Hexi Road, Sanhe Village, Tonghu Town, Zhongkai High-tech Zone, Huizhou City
Tel: +86-752-7987222
Mobile: +86-18123965666
Fax: +86-752-7987000
Email: sales011@xycgd.com
Website: http://www.xycgd.com