Frequently Asked Questions

Here are answers to some frequently asked questions:

If you have different questions then please contact me using the email address at the bottom of this page.

Why do I need a light integrator?

Many photographers are happy to expose their prints using time-based exposures. This is sufficient for many people.

However, all light sources vary in intensity (some more than others). For example many take time to warm-up, and others fluctuate during the exposure if the mains electricity supply is unstable (this is much more common than you may think). Varying UV intensity makes it very difficult to make consistent prints when using time-based exposures.

The most demanding printers use light integrators to automatically adjust their printing time to allow for variations in UV intensity.

Why do I need to calibrate the sensors?

Calibration does two things:

  1. It converts the raw UV measurements into things called ‘units’ (see below)
  2. It helps to eliminate measurement errors due to placement of the sensors

The second point is important. All light sensors are highly sensitive to the distance from the light source they are measuring, plus their orientation to the light source. Turning a sensor by just 10 to 15 degrees can have a significant effect on its measurements. Calibration helps to eliminate this error.

If you want to use the system for sun printing, then please see the sun printing FAQ below.

What is a ‘unit’ of exposure?

The light integrator measures UV intensity in micro-Watts per centimeter squared (µW/cm2), which is meaningless to most photographers. Calibration allows the light integrator to convert this raw measurement into things called ‘units’. These are much easier to use when printing.

After calibration, one ‘unit’ is about one second of exposure when the lights are at full power.

The light integrator does the necessary calculations and adjustments automatically, and ensures that your prints get the same exposure regardless of the crazy stuff your lights are doing. You can even switch off your lights for a while during an exposure, and the light integrator will sort it out.

Is it easy to change from time-based exposures to ‘units’?

Yes, in just three steps:

  1. Calibrate the light integrator
  2. Convert your old exposure times in seconds straight to units
  3. Make some test prints to refine the exposure ‘units’ to use

For example, a time-based exposure of 3½ minutes is 210 seconds. So the initial conversion would be to 210 units.

Where should I place the UV sensor?

Ideally, the UV sensor should be positioned as close as possible to the printing area. This isn’t always feasible so the system is designed to allow a great deal of flexibility. As long as the sensor position and orientation relative to the light source is fixed, then the calibration process will sort out the rest.

I use two sensors in my UV exposure unit: one on each side of my vacuum frame pointing directly at the light.

Does the light integrator need to be close to the sensors?

I have tested the Light Counter system with 5m cables between the sensors and light integrator.

If you are working in an environment with lots of electromagnetic noise (e.g. industrial settings, or near motors, pumps or very high power switching light systems), then shorter cables may be necessary.

I do not recommend connecting multiple cables together because this will also reduce the signal quality and may cause the system to not work.

Do not use ‘active’ USB extension cables. These do not work with the system.

If I move the UV sensor, will my exposures change?

So long as you calibrate the light integrator after moving the sensor, then this will not have a noticeable effect. The calibration process will adjust for the changed position.

If I move my UV light source, then should I recalibrate the light integrator?

This is tricky because the answer depends upon exactly things have moved relative to each other.

If the distance from the light source to the print has changed, then inevitably the necessary exposure time will also change. But if the sensor is much closer to the print area than to the lights, then you probably won’t need to recalibrate because the integrator will adjust for the changed light source position.

In the worst case, you may need to recalibrate the light integrator and then make some test prints to determine a new standard printing time for the new light source position.

If I upgrade my light source, then will my exposures change?

If you upgrade to higher power lights then your exposures will be shorter. Assuming the positions of the light source, print area and sensor have not changed, then there will be no need to recalibrate the light integrator because it will automatically adjust to the brighter lights.

If the light source position has also changed relative to the printing area, then you will need to recalibrate the light integrator and then make some test prints to determine a new standard printing time for the new configuration.

If I replace a UV sensor, then will my exposures change?

The second generation UV sensors are factory calibrated using a standard light source. This means that all second generation sensors should be within a couple of percent of each other. These can therefore be swapped with minimum impact.

After swapping a sensor (first or second generation) I recommend recalibrating the light integrator and doing some test prints to verify that no change has happened.

Why should I care about the temperature inside my UV exposure unit?

High temperatures during exposure can cause problems with many alternative printing processes. Many people, especially in hot climates, install exhaust fans in their exposure units in an attempt to keep them cool. Measuring the temperature inside the exposure unit is the only way to know if this is necessary and effective.

How should I connect the power controller?

The power controller is connected using standard ‘kettle’ type connectors (technically called ‘C13’ and C14’ connectors). The C13 connector (standard ‘kettle’) is used for the mains electricity supply. The C14 (‘kettle extension’) is used to connect the light source.

C13 and C14 Connectors
C14 Connector (left) and C13 Connector (right)
C14 Cable (left) and C13 Cable (right)

I do not supply these cables with the power controller because power connections vary considerably around the world, you may already have these anyway, and it will always be cheaper for you to buy them locally.

If you are unsure then please consult a qualified electrician.

Does the system work without the power controller?

Yes. The light integrator works very well without the power controller. About half of my customers use a power controller, and about half do not.

When you start an exposure, the light integrator only begins counting when it detects UV light. This allows plenty of time for you to switch on the lights by hand.

When the exposure is completed, the light integrator beeps, which is your cue to switch off the lights.

I am a sun printer. Will the Light Counter system work for me?

The Light Counter system is designed for darkroom use. However, some sun printers are using LC2 (first generation) devices for printing outside. These work well when powered by USB battery packs. When using for sun printing, it does not make sense to calibrate the light integrator because the sun is unstable and infinitely variable: just use it uncalibrated.

In certain configurations the LC3 (second generation) light integrator may work from a battery, but in general it needs to be connected to a mains electricity supply because the big display consumes more power than battery packs can typically provide.

Does the Light Counter system work for silver gelatin prints?

The LC2 (first generation) light integrator had a visible light sensor that worked well for long exposures over about 30 seconds. The LC3 (second generation) light integrator is designed for use with UV light only.

If you would like a light integrator for silver paper and/or film, then please contact me to discuss your requirements. My email address is at the bottom of this page.

Does the Light Counter system work with NuArc exposure units?

The light integrator will work with any UV light source, so long as the sensor can be placed where the light can reach it.

The power controller only works with exposure units that have their lights on a separately switched circuit (it works by switching the mains electricity on and off). Therefore NuArcs and other integrated exposure units cannot be switched by the power controller.

Other light integrators with the same capabilities cost thousands of dollars. How do you manage to make this system so cheap?

I know how difficult and expensive it is to equip a photography darkroom, so I have worked hard to optimise costs at all levels:

  • By designing a system that allows you to only buy the devices you need for your printing choices
  • By making sensible component decisions, so there is nothing unnecessary inside the box
  • By doing all design and critical manufacturing steps myself, so I have no costly outsourcers to deal with
  • By using 3D printed device enclosures of my own design, which is ideal for low volume, cost-effective manufacturing

Can you make custom-designed devices for specialist needs?

Please contact me to discuss your requirements. My email address is at the bottom of this page.

What are the warranty terms?

All Light Counter kits, devices, and sensors are covered by a global repair-or-replace warranty. If a component fails within a year of delivery, then just ship it back to me and I will repair or replace the item free of charge.

Please note that the following actions will invalidate the warranty:

  • Do not connect a computer to the sensor USB ports. These use standard USB cables for reasons of cost and convenience, but they do not use the USB protocol. Connecting a computer may damage the device or your computer
  • Do not open the device enclosure. The devices contain static-sensitive components. Opening the enclosure and touching components may damage them
  • Do not overload the power controller with high power lights. The standard power controller is rated for a maximum 5A load. The professional power controller is rated for a maximum 10A load. They may both work when over-loaded but over time this may damage the internal components. If you are unsure then please consult a qualified electrician