Light Sensors, Ambient Light Sensors

Light Dependent Resistor (LDR), Photoresistor (CdS)

Token Electronics now offers commercial grade PGM photoresistor. Designated the PGM Series, the photoresistors are available in 5mm, 12mm and 20mm sizes, the conformally epoxy or hermetical package offer high quality performance for applications that require quick response and good characteristic of spectrum.

SMD Phototransistors, Chip Ambient Light Sensors

Ambient light sensors (ALS) will also be known as illuminance or illumination sensors, photodetector, brightness sensors, photo transistor, optical sensors, or simply light sensors. One essential application for ALS technologies are mobile phones. Inside a mobile phone, the ALS enables automatic charge of display backlight brightness over an array of illumination conditions from the dark atmosphere to sunlight.

Light Sensors (Phototransistor, Ambient Light Sensor) Glossary

Absolute Maximum Ratings: Maximum value of limit per each item.

Operating Temperature (Topr): Allowable temperature range of power application.
Usually when the operating temperature increases, the power consumption decreases. In addition, the power application is prohibited when the actual operating temperature is out of range. In the case of a phototransistor, the temperature that can be applied is not described as the surface temperature of the package, but is described as working temperature (the ambient air temperature around the device).

Storage Temperature (Tstg): In the stored state, allowable temperature range when power is not applied.

Power Dissipation (PC): When the operating temperature is 25°C, the light receives the allowable power dissipation of the phototransistor. Often, as the ambient temperature increases, the allowable power consumption (PC) tends to drop.

Collector Current (IC): When the light-receiving phototransistor conducts current at 25°C ambient temperature, the maximum allowable collector current flows through the phototransistor in the permissible power dissipation (PC) range.

Peak wavelength (λp): λp Is the most sensitive wavelength value of the phototransistor, measured in nanometers (nm). The Phototransistor responds to the light from the wavelength range of the fluorescence or incandescent light source, and when matched with the IR LED light source, they perform optimally. This is because the phototransistor has a peak spectral response at approximately 840nm of near-infrared.

    Breakdown Voltage: (VBR): VBR is the maximum voltage allowed between the collector and emitter. Exceeding the maximum voltage can cause permanent damage to the phototransistor. The breakdown voltages are 100% sorting parameters.
  • Collect-emitter breakdown voltage Bvceo: typically ranges from 20 V to 60 V.
  • Emitter-collector breakdown voltage Bveco: typically ranges from 3 V to 7 V.

Collector to Emitter Voltage: (VCEO): The maximum voltage is allowed between the collector and the emitter on light-receiving side, and when no forward current flows through the led of the light emission side (the indicator light does not emit light). Under normal circumstances, when the power supply voltage close to this value, the transient operating trajectory can not be maintained at the actual maximum operating temperature of the allowable power range, in the process of switching, the device may occur over power damage. Note that the supply voltage is kept within a sufficient safe range so that no excessive power loss occurs even during this switching moment.

Emitter to Collector Voltage (VECO): The allowable reverse voltage of the phototransistor that can be applied to the light receiving side. Typically, the voltage depends on the reverse withstand voltage between the emitter and the base of the phototransistor, or below the reverse withstand voltage. Damage or irreversible damage may occur if a reverse voltage exceeding this value is applied.

Rise Time/ Fall Time
Rise Time/ Fall Time

Collector Dark Current (Iceo): When the phototransistor is in the dark and a voltage is applied from the collector to the emitter, a certain amount of current will flow. This current is called a dark current. The current consists of the collector-base junction leakage current and the transistor's DC current gain. The presence of this current prevents the phototransistor from being considered "off", or is ideal for "on" the switch. The dark current is specified as the maximum collector current that allows flow at a given collector-emitter test voltage. The dark current is a function of the applied collector-emitter voltage and ambient temperature. Dark current increases with increasing temperature. This value is usually specified at 25°C. The value of the load resistance must be designed with the maximum value of the current within the conditions of use.

Collector-Emitter Saturation Voltage (Vce(sat)): Saturation is the state in which both the emitter base and the collector base of the phototransistor become forward based. From a practical point of view, the collector-emitter saturation voltage Vce(sat) is a factor that represents the proximity switch (closed state) of the photodetector. This is because Vce(sat) is the voltage that drops when the detector is in the "on" state. Vce(sat) is usually the maximum allowable collector emitter voltage given the specified light intensity and collector current value.

IR Receiving Current (IL(4)): The infrared phototransistor acts as a transistor, and its basic voltage is determined by the amount of light that impinges on the transistor.Therefore, it acts as a variable current source. More IR light will cause a larger current to flow through the collector-emitter lead. IL(4) is specified at VEC = 5V, IR LED 850nm.

    Rise Time/ Fall Time:
  1. Pulse Rise Time tr: The photosensitive transistor adjusts the input pulse light under the specified working conditions, so that the photosensitive transistor output the corresponding pulse current to the specified value to output the time required for 10%-90% of the pulse front amplitude.
  2. Pulse Fall Time tf: The time required to output the pulse along the magnitude of 90%-10%.
  3. Pulse Delay Time td: The time required to start from the input pulse to 10% of the leading edge of the output electrical pulse.
  4. Pulse Storage Time ts: The time required for the output electrical pulse to drop to 90% of the pulse amplitude after the input pulse has been completed.

Download Ambient Light Sensor Glossary in PDF file.

Table 1 - Photoelectric Characteristics (Ta=25°C) PT-IC-GC-3-PE-520

Parameter Symbol Condition Min. Typ. Max. Unit
Photo Current IL(1) Vcc=5V
1.2 2.5 3.6 μA
IL(2) Vcc=5V
3.6 7.5 10.8 μA
IL(3) Vcc=5V
12 25 36 μA
Collector Dark Current ID Vcc=5V/85°C
- - 0.8 μA


   Table 2 - PT-IC-GC-3-PE-520 Batch BINNED GROUP

Batch BINNED GROUP (Tamb = 25 °C, unless otherwise specified)
Parameter Condition Binned Group Symbol Min. Max. Unit
Photo Current EV = 100 lux, CIE illuminant A, VCE = 5 V A IPCE 12 23 μA
B IPCE 19 36 μA

Figure 3 - Typical Optical Load Circuit
Figure 3 - Typical Optical Load Circuit

Token provides ambient light sensor for photodiode and phototransistor. For a given irradiance, the phototransistor may show a batch change of the output current due to the susceptibility of the wafer and the variability of the transistor gain. The lot-to-lot change of the photoelectric sensor is significantly lower because it is only caused by the variability of photosensitivity. Token provides phototransistor output (component) for its ambient light sensor in binned groups (Table 2). These groups can not be ordered separately, but each reel is labeled A, B, or C, which allows the user to select the appropriate load resistance to compensate for these wide tolerances.

Select The Load Resistor

In order to minimize the output variability of the light sensor, the load resistance (RL) requires the selection of the component to choose the load resistance (RL) according to the sorted standard illuminance. The ambient light sensor and the transistor output of the typical optical circuit shown in Figure 3. For the PT-IC-GC-3-PE-520, 30 lux the typical output current is 7.5 μA. At 100 lux, the typical output current is 25 μA and the output current is in the range of 12 μA to 36μA. By the previously mentioned binning components, the range of 100 lux is divided into two bins. Each bin should use a different load resistor, and the output is relatively consistent for a given lux level.

Suppose application detection ranges from 10 lux to $1000 lux. Use a 10 KΩ load resistor to produce a voltage of 0.025 V to 2.5 V. The photocurrent of the voltage is equal to 2.5 μA to 250 μA.

   Table 3 - Mean of Bin

Part Number Bin Photocurrent, IPCE at 100 lux (μA)
Min. Mean Max.
PT-IC-GC-3-PE-520 A 12 17.5 23
B 19 27.5 36

The purpose of selecting the resistance is to have the same output voltage for the average of each component, Table 3.

   Table 4 - Load Resistor of Bin

Bin A Bin B
IPCE = 17.5 μA, RL = 10 kΩ
V = 17.5 μA x 10 kΩ
V = 175 mV
0.175 V = 0.0000275 A x RL
RL = 0.175 V/0.0000275 A
RL = 6.36 kΩ

The PT-IC-GC-3-PE-520 overall tolerance is reduced from 12 to 36 by 12 to 23 by changing the resistance value based on the bin.

Download Select The Load Resistor in PDF file.

Light Sensors Summary Table

Category Thumb Nail Part NO. Infrared Ray Lens Color Spectral Bandwidth
Photo Current Dark Current
10Lux 30Lux 100Lux 0Lux
Φ3 Plate Edge PT-A6-BC-3-PE-520 IR Receiving Dark Blue 520 3 ~ 12 9 ~ 36 30 ~ 120 0.2Max.
PT-IC-BC-3-PE-550 IR Receiving Dark Blue 550 1.5 ~ 5.0 4.5 ~ 15 15 ~ 50 0.8Max.
PT-IC-GC-3-PE-520 IR Receiving Dark Green 520 1.2 ~ 3.6 3.6 ~ 10.8 12 ~ 36 0.8Max.
PT-IC-AC-3-PE-550 IR Receiving Water Clear 550 7 ~ 15 21 ~ 54 70 ~ 180 0.8Max.
PT-A1-AC-3-PE-850 IR Blocking Water Clear 850 3 ~ 6 9 ~ 18 30 ~ 60 0.1Max.
Φ5 Plate Edge PT-IC-GC-5-PE-520 IR Receiving Dark Green 520 2 ~ 6 6 ~ 18 20 ~ 60 0.8Max.
PT-IC-BC-5-PE-550 IR Receiving Dark Blue 550 2.5 ~ 5.5 7.5 ~ 16.5 25 ~ 55 0.8Max.
PT-IC-AC-5-PE-550 IR Receiving Water Clear 550 7 ~ 18 21 ~ 54 70 ~ 180 0.8Max.
PT-A2-AC-5-PE-850 IR Blocking Water Clear 850 1.5 ~ 4.5 4.5 ~ 13.5 15 ~ 45 0.1Max.
Φ5 Helmet Edge PT-A1-AC-5-HE-850 IR Blocking Water Clear 850 4.5 ~ 9.0 13.5 ~ 27 45 ~ 90 0.1Max.
Φ5 Plate None PT-A6-AC-5-PN-580 IR Receiving Water Clear 580 2.5 ~ 10 7.5 ~ 30 25 ~ 100 0.2Max.
PT-IC-BC-5-PN-550 IR Receiving Dark Blue 550 2.5 ~ 5.5 7.5 ~ 16.5 25 ~ 55 0.8Max.
PT-IC-AC-5-PN-580 IR Receiving Water Clear 580 1.5 ~ 5.5 4.5 ~ 16.5 15 ~ 55 0.8Max.
PT-A4-AC-5-PN-850 IR Blocking Water Clear 850 5 ~ 12 15 ~ 36 50 ~ 120 0.1Max.
PT-A2-AC-5-PN-850 IR Blocking Water Clear 850 1.5 ~ 4.5 4.5 ~ 13.5 15 ~ 45 0.1Max.
Φ3 Bullet Edge PT-A2-AC-3-BE-850 IR Blocking Water Clear 850 15 ~ 45 45 ~ 145 150 ~ 450 0.1Max.
PT-A2-DC-3-BE-940 IR Blocking Dark 940 - - - 0.1Max.
Φ5 Bullet Edge PT-A2-AC-5-BE-850 IR Blocking Water Clear 850 30 ~ 90 90 ~ 270 300 ~ 900 0.1Max.
PT-A1-FC-5-BE-940 IR Blocking Dark 940 - - - 0.1Max.
Φ5 Bullet None PT-A6-AC-5-BN-520 IR Receiving Water Clear 520 5 ~ 22 15 ~ 66 50 ~ 220 0.2Max.
PT-IC-AC-5-BN-520 IR Receiving Water Clear 520 4 ~ 12 12 ~ 36 40 ~ 120 0.8Max.
PT-A1-DC-5-BN-940 IR Blocking Dark 940 - - - 0.1Max.
SMD PT-B1-DC-0603-940 IR Receiving Dark 940 - - - 0.1Max.
PT-A8-AC-1206-850 IR Receiving Water Clear 850 0.5 ~ 1.2 1.5 ~ 3.6 5 ~ 12 0.1Max.
PT-IC-BC-3528-550 IR Blocking Dark Blue 550 1.5 ~ 4.5 4.5 ~ 13.5 15 ~ 45 0.1Max.
PT-IC-AC-3528-520 IR Blocking Water Clear 520 7 ~ 18 21 ~ 54 70 ~ 180 0.8Max.
PT-A1-AC-3528-850 IR Blocking Water Clear 850 2.5 ~ 5.0 7.5 ~ 15 25 ~ 50 0.1Max.
CdS (PGM5) PGM5506 IR Blocking Epoxy Resin 540 2 ~ 6 - - 0.15Min.
PGM5516 IR Blocking Epoxy Resin 540 5 ~ 10 - - 0.2Min.
PGM5526 IR Blocking Epoxy Resin 540 8 ~ 20 - - 1.0Min.
PGM5537 IR Blocking Epoxy Resin 540 16 ~ 50 - - 2.0Min.
PGM5539 IR Blocking Epoxy Resin 540 30 ~ 90 - - 5.0Min.
PGM5549 IR Blocking Epoxy Resin 540 45 ~ 140 - - 10.0Min.
PGM5616D IR Blocking Epoxy Resin 560 5 ~ 10 - - 1.0Min.
PGM5626D IR Blocking Epoxy Resin 560 8 ~ 20 - - 2.0Min.
PGM5637D IR Blocking Epoxy Resin 560 16 ~ 50 - - 5.0Min.
PGM5639D IR Blocking Epoxy Resin 560 30 ~ 90 - - 10.0Min.
PGM5649D IR Blocking Epoxy Resin 560 50 ~ 160 - - 20.0Min.
PGM5659D IR Blocking Epoxy Resin 560 150 ~ 300 - - 20.0Min.
PGM5506-MP IR Blocking Hermetical 540 2 ~ 6 - - 0.15Min.
PGM5516-MP IR Blocking Hermetical 540 5 ~ 10 - - 0.2Min.
PGM5526-MP IR Blocking Hermetical 540 8 ~ 20 - - 1.0Min.
PGM5537-MP IR Blocking Hermetical 540 16 ~ 50 - - 2.0Min.
PGM5539-MP IR Blocking Hermetical 540 30 ~ 90 - - 5.0Min.
PGM5549-MP IR Blocking Hermetical 540 45 ~ 140 - - 10.0Min.
CdS (PGM12) PGM1200 IR Blocking Epoxy Resin 560 2 ~ 5 - - 1.0Min.
PGM1201 IR Blocking Epoxy Resin 560 4 ~ 10 - - 2.0Min.
PGM1202 IR Blocking Epoxy Resin 560 8 ~ 20 - - 5.0Min.
PGM1203 IR Blocking Epoxy Resin 560 18 ~ 50 - - 10.0Min.
PGM1204 IR Blocking Epoxy Resin 560 45 ~ 150 - - 20.0Min.
PGM1205 IR Blocking Epoxy Resin 560 140 ~ 300 - - 20.0Min.
PGM1200-MP IR Blocking Hermetical 560 2 ~ 5 - - 1.0Min.
PGM1201-MP IR Blocking Hermetical 560 4 ~ 10 - - 2.0Min.
PGM1202-MP IR Blocking Hermetical 560 8 ~ 20 - - 5.0Min.
PGM1203-MP IR Blocking Hermetical 560 18 ~ 50 - - 10.0Min.
PGM1204-MP IR Blocking Hermetical 560 45 ~ 150 - - 20.0Min.
PGM1205-MP IR Blocking Hermetical 560 140 ~ 300 - - 20.0Min.
CdS (PGM20) PGM2000 IR Blocking Epoxy Resin 560 2 ~ 5 - - 1.0Min.
PGM2001 IR Blocking Epoxy Resin 560 4 ~ 10 - - 2.0Min.
PGM2002 IR Blocking Epoxy Resin 560 8 ~ 20 - - 5.0Min.
PGM2003 IR Blocking Epoxy Resin 560 18 ~ 50 - - 10.0Min.
PGM2004 IR Blocking Epoxy Resin 560 45 ~ 150 - - 20.0Min.
PGM2005 IR Blocking Epoxy Resin 560 140 ~ 300 - - 20.0Min.
PGM2000-PP IR Blocking Plactic Case 560 2 ~ 5 - - 1.0Min.
PGM2001-PP IR Blocking Plactic Case 560 4 ~ 10 - - 2.0Min.
PGM2002-PP IR Blocking Plactic Case 560 8 ~ 20 - - 5.0Min.
PGM2003-PP IR Blocking Plactic Case 560 18 ~ 50 - - 10.0Min.
PGM2004-PP IR Blocking Plactic Case 560 45 ~ 150 - - 20.0Min.
PGM2005-PP IR Blocking Plactic Case 560 140 ~ 300 - - 20.0Min.

Download Light Sensors Summary Table in PDF file.

What is Phototransistors?

The environmentally friendly phototransistor is a combination of photodiode and amplifier integrated in a single chip. This integrated combination is used to overcome the main uniform gain limits of the photodiode. Many modern applications require the output signal from the photodetector to produce even larger than the single photodiode. Although the signal from the photodiode can always be amplified by using an external op amp or other circuit, this method is generally less practical or cost effective than using a phototransistor.

The phototransistor can be viewed as a photodiode whose output photocurrent signal is fed to the base of the transistor. When the device is not required to operate as a photodetector, the base is usually connected to allow the designer to use the base current to bias the transistor. The typical gain of the phototransistor can range from 100 to 1500. The current-voltage characteristics of the phototransistor are similar to those of the NPN signal transistor. The only difference is that the incident light provides the base drive current.

The structure of environmentally friendly phototransistor is very similar to the structure of photodiode. In fact, when optimized for this mode of operation, the collector-base junction phototransistor can be used as having a fairly good photodiode, with the main structural difference being that the phototransistor is two more junctions than the photodiode.

Phototransors are suitable for detecting light or brightness in a manner similar to that of the human eye. They are most commonly found in industrial lighting, consumer electronics and automotive systems, which can be automatically adjusted according to ambient light conditions. By turning on, off or adjusting the function, ambient light sensors can save battery power and provide additional security without the need for manual adjustment. Token Electronics offers a wide range of ambient light sensors, with pin-type and surface-mount patches, photodiode or phototransistor outputs.

Ambient Light Sensor Product Category

Ambient Light Sensors Light Dependent Resistor (LDR)
Photoresistor (CdS)
Cds Advantages: similar to the human eye.
Disadvantages: Cadmium, ROHS prohibited substances.
Photodiode Cds Advantages: The uniformity of the photodiode between the units is relatively high.
Disadvantages: low current output, the need for external amplification circuit.
Photosensitive Sensor
Photosensitive Triode
Cds Advantages: with amplifier circuit, photoelectric transistor output current.
Disadvantages: poor temperature characteristics.
Photo IC Cds Advantages: amplification, logic control, switches and other integrated features
Disadvantages: high dependence on professional products.

Why Use Environmentally Friendly Phototransistor?

Environmental protection phototransistor is known as phototransistor, photosensitive sensor, environmentally friendly photosensitive triode, ambient light sensor. The environmentally friendly phototransistor is a solid state photodetector with internal gain. This makes them more sensitive to photodiode on the same area basis and can be used to provide analog or digital output signals. Phototransistor series of detectors provide the following characteristics:

  • Cost-effective photoelectric detector, detection range from visible to near infrared.
  • 100 to 1500 gain.
  • Moderate response time.
  • Can be used for a variety of packaging, including epoxy coating, transfer molding, casting, sealed packaging and chip form.
  • Replace the traditional CDS photoresistor, non-cadmium, lead and other harmful substances, in line with the EU ROHS standards.
  • Can be used for almost any visible or near infrared light source, such as IRED, neon, fluorescent, incandescent bulbs, lasers, fire, sun and so on.

Source Lighting Guide

Light Source Illumination (Lux) ALS Circuit Symbol
Moonlight 0.1 Circuit Symbol
60W Light Bulb @1m 50
1W MES Light Bulb @0.1m 100
Fluorescent Light 500
Bright Sunshine 30,000


Most photodiodes and phototransistors have an epoxy filter function that increases the relative spectral sensitivity and makes it closer to the human eye's sensitivity. This is sometimes called the v(λ) curve. The part number contains the letter part of the FC with this epoxy resin. Figure 1 shows an ambient light sensor without epoxy filtering, and Figure 2 shows a sensor with epoxy filter. For this epoxy filter, the bandwidth (λ0.5) is reduced from 430 nm to 800 nm to 430 nm to 600 nm.

Figure 1 - No Epoxy Filter
Figure 1 - No Epoxy Filter
Figure 2 - Epoxy Filter
Figure 2 - Epoxy Filter

Download Guide to Ambient Light Sensors in PDF file.