What Is Auto-Gating in Night Vision Tubes?

Auto-gating is a power supply feature that switches an image intensifier tube’s photocathode voltage on and off very rapidly, and shortens the on-time as the scene gets brighter. It keeps the image usable when headlights, street lights or dawn appear, and it protects the tube from bright light. JOVSTAR Class B and Class A tubes are auto-gated and keep 54 lp/mm resolution at 200 lx. For the full tube range, see our image intensifier tube selection guide.

The Problem Auto-Gating Solves

An image intensifier tube is built to amplify starlight many thousands of times. When a bright light enters the view, such as a car’s headlights, a torch or a lit building, a tube with a normal power supply has too much signal:

• bright areas bloom and wash out the surrounding detail;
• the image takes time to recover after the light goes away;
• repeated exposure to bright light can shorten the tube’s life.

For users who move between dark areas and lit ones, such as patrols near roads, towns and industrial sites, this makes a normal tube hard to use.

How Auto-Gating Works

The photocathode only turns light into electrons while a voltage is applied to it. An auto-gating power supply switches that voltage on and off many times per second. In darkness, the photocathode is on almost all the time and the tube works at full gain. As the scene brightens, the power supply automatically shortens each on-period, so less signal enters the tube. To the eye the image stays steady, because the switching is far too fast to see.

The result is a tube that adjusts itself over a very wide range of light. JOVSTAR auto-gated tubes are specified for a working illumination range starting from 1×10⁻⁶ lx, a level far below starlight.

Auto-Gating vs Bright-Light Protection

Many tubes also have a bright-source or strong-light protection circuit that reduces the tube’s output when the overall light level is too high. JOVSTAR tubes have strong-light protection and polarity-reversal protection in all three classes. Auto-gating goes further: it acts quickly on the photocathode, preserving detail and resolution in mixed lighting rather than simply dimming the image.

What Auto-Gating Changes in the Specifications

Parameter	Class C (normal)	Class B (auto-gating)	Class A (auto-gating)
High-light resolution (200 lx)	—	54 lp/mm	54 lp/mm
Resolution	60 lp/mm	64 lp/mm	68 lp/mm
FOM	1400	1600	1800
Operating current	15 mA	25 mA	25 mA
Power consumption	33–51 mW	55–85 mW	55–85 mW

The main difference is the high-light resolution: an auto-gated tube keeps 54 lp/mm at 200 lx, about the light level of an indoor room. The cost is a little more power: 25 mA instead of 15 mA, which still allows long runtimes from a single 3 V cell.

When You Need Auto-Gating

1. Mixed urban and rural use: patrols that pass street lights, vehicles and buildings.
2. Driving with night vision: oncoming headlights and road lighting.
3. Search and rescue: torches, vehicle lights and flares at an incident scene.
4. Dawn and dusk: work that continues as the light changes.

For observation in consistently dark, remote areas, a Class C tube with a normal supply can be enough, and it uses the least power.

Which JOVSTAR Tube Fits Your Device

• Auto-gated, balanced: Class B, FOM 1600.
• Auto-gated, highest performance: Class A, FOM 1800, gain up to 20,000 cd/m²/lx.
• Lowest power for dark environments: Class C, FOM 1400, 15 mA.

All classes are available in the JV-IT64, JV-IT1D, JV-IT20, JV-IT24 and JV-IT60 series. For how class affects image quality, see image intensifier FOM explained. Our engineers can recommend a class for your device through our OEM and ODM service.

FAQ

Which JOVSTAR tubes are auto-gated?

Class B and Class A tubes in all five JOVSTAR series are auto-gated. Class C tubes use a normal power supply.

Does auto-gating use more power?

Slightly. JOVSTAR auto-gated tubes draw 25 mA (55–85 mW) compared with 15 mA (33–51 mW) for Class C, still low enough for a single 3 V cell.

Do I need auto-gating for rural use?

For consistently dark, remote areas, a Class C tube can be enough. Auto-gating is most useful where users meet street lights, vehicle lights or changing light at dawn and dusk.