A Day in the Lab: Metal Halide vs LED Illumination
Alex and Sam both have a full day of fluorescence microscopy ahead of them. Same sort of samples, same deadline, similar microscopes. There is, however, one fairly important difference.
Alex is using a metal halide light source. Sam has CoolLED LED illumination.
Over the course of a working day, that seemingly small difference can affect everything from when imaging starts to how much time gets spent waiting, adjusting, replacing and generally faffing around with the illumination system.
So, clocks at the ready.
Lights on
Alex switches on the metal halide lamp.
Now comes the warm-up. Arc lamps need time to reach suitable operating conditions before serious fluorescence imaging can begin, so Alex isn't going anywhere just yet.
Coffee, then.
Sam switches on the CoolLED system.
It's on.
That's it. Sam starts imaging.
And we're off
Alex can finally get started.
Arc-lamp performance depends on the condition and alignment of the bulb, while output gradually changes as the lamp ages. Getting good, even illumination therefore means having a few more variables to keep an eye on.
Sam has already imaged several samples.
This is becoming slightly awkward.
Things are warming up
Quite literally, in Alex's case.
Metal halide lamps generate a substantial amount of unwanted heat. That means cooling, fans and additional thermal load around the microscope, with much of the electrical energy ultimately ending up somewhere other than in the fluorescence image.
LED illumination produces far less unwanted heat and can be switched electronically between exposures.
The sample therefore doesn't need illuminating while nobody's actually taking a picture of it.
It turns out fluorophores quite like that arrangement too.
The bulb incident
Today happens to be replacement day.
The old metal halide bulb has reached the end of its useful operating life, so imaging stops. The lamp needs to cool sufficiently before it can be handled, then the replacement bulb has to be installed.
Depending on the system, there's also alignment to think about before another warm-up period begins.
Thrilling stuff.
Sam eats a sandwich.
Then carries on imaging.
Round two
Alex is finally running again with a fresh lamp.
Unfortunately, replacing an ageing bulb also means moving from one point in a lamp's lifetime to another. Arc-lamp output changes as the bulb ages, adding another consideration when trying to keep imaging conditions consistent between experiments.
LED illumination provides controllable, repeatable output without routinely replacing bulbs or realigning the light source.
Sam remains irritatingly relaxed.
Home time
Alex finishes for the day.
There's still the spent lamp to deal with. Metal halide lamps contain mercury, which means they require appropriate handling and disposal rather than simply disappearing into the nearest bin.
A lovely final administrative flourish.
Sam switches the LED system off.
Both researchers technically spent the day in the lab.
Only one of them spent quite so much of it thinking about their light source.
Perhaps illumination shouldn't be this complicated
Metal halide illumination was a major step forward for fluorescence microscopy, and plenty of systems are still doing useful work in laboratories today.
But warm-up periods, ageing bulbs, heat, alignment, replacement and hazardous lamp disposal all create jobs that have very little to do with the actual science.
LED illumination removes much of that routine maintenance and waiting around. Switch it on, select the intensity and get on with imaging.
Sometimes the nicest upgrade to a day at the microscope is simply having fewer things to faff about with.
