Flash Mode: Photon+ and a Sensor Fast Enough to Catch a Speedlight

“tl;dr

The original Photon sensor was too slow for flash metering, so we built our own from scratch. It works. Flash mode is coming as part of Photon v2 - in the meantime, build v1 and we’ll make sure the upgrade path is simple.”

The Problem With Flash

Since we published the original Photon light meter build, the most common question has been: will it get a flash mode? The honest answer for a long time was no - the BH1750 sensor at the heart of v1 is just low on temporal resolution to provide a signal that we can use to integrate the light level over such short times. It is essentially blind to it.

The Immovable Object vs The Unstoppable Stubbornness

But wait… rather than admit defeat, we learned about fast OpAmps and built our own sensor from scratch, using fast components that would measure light on the timescales that you need to measure flash accurately.

To stress-test the new sensor, we used it with an old Nikon Speedlight (SB800). Speedlights fire for a very short duration at lower powers (source: Andy Gock). The graph shows the light intensity** against time since firing for all of the Flash’s power settings.

Peanut for scale

Putting It Through Its Paces

To stress-test the sensor we grabbed an old Nikon SB-800 Speedlight - a good choice because Speedlights are notoriously brief at low power settings, where flash durations can drop into the tens of microseconds. The graph below shows light intensity against time-since-firing across every power setting on the SB-800.

The graph reveals something useful about how most flashes actually work: they don't reduce output by firing more gently. They fire at full intensity and cut it short earlier. The practical upshot: if you want to freeze fast motion with flash, lower power settings are often your friend. Less light, yes - but also a significantly shorter pulse.

What This Means for Photon v2

The new sensor is built and tested. We're now incorporating everything we learned from v1 (the things that worked, the things we'd do differently) into a second version of Photon that will have flash metering built in. We're being deliberate about it rather than rushing, and we don't have a concrete release date to share yet.

Our honest recommendation: build v1 now. It's a capable incident meter and you won't be throwing it away - we're committed to a straightforward upgrade path from v1 to v2 when it arrives. The core hardware investment carries over.