A xenon light source datasheet is decided by four numbers: lamp power, total optical power, spot size and divergence, and output stability. A 300 W lamp that delivers 50 W of total optical power is not a 300 W source at the sample plane — electrical watts are the input, optical watts are what the experiment actually sees.
The wattage in a model name describes what the bulb draws, not what reaches the reactor. On a PLS-SXE300E the lamp power is adjustable from 150–300 W, while the total optical power is 50 W. The gap is not a defect: it is heat, reflector spill, and radiation that never enters the collection cone.
This matters because buyers negotiate on the first number and then run experiments on the second. Two sources both labeled 300 W can differ substantially in delivered optical power, and no amount of extra electrical input compensates for a collection geometry that throws light away before the shutter.
Read the sheet in this order: optical power first, then the spectral range over which that power is distributed, then the geometry that concentrates it. Wattage tells you what the power supply and the cooling system have to handle. It tells you very little about photon flux at your catalyst.
Only four figures change the outcome of a photocatalysis experiment, and each answers a different question. The table pairs every figure with the question it settles, plus a way to check it on arrival.
| Datasheet figure | What it describes | What it controls in your experiment | How to verify it |
|---|---|---|---|
| Lamp power | Electrical input to the bulb; 150–300 W adjustable on a 300 W unit | Headroom, and the spectrum shape at the power you will actually use | Compare the supply readout with the set point at three levels |
| Total optical power | Radiant power collected at the exit; 50 W on a 300 W unit | The ceiling on irradiance at any working distance | Optical power meter at the exit port |
| Spot size and divergence | Beam geometry after the collimating optics | Irradiance at the sample plane and how much of the reactor is lit | Target and ruler at two working distances |
| Output stability | Variation of output over time at fixed power | Whether rates measured hours apart can be compared | Logged irradiance across a full run |
The last row is where most sheets turn vague. Stability often appears as a single percentage with no interval attached, which makes vendors incomparable. Ask what period the figure covers, whether it includes the warm-up phase, and whether it is peak-to-peak variation or long-term drift. A source that holds steady through a short screening run can still walk away across a full working day.
Irradiance is optical power divided by illuminated area, so the same source produces a different value at every working distance. A 50 W output concentrated into a small spot and the same 50 W spread over a wide field are not interchangeable, even though the datasheet line reads identically.
Divergence is the number that tells you how fast that spot grows as you move the reactor away from the port. When it is missing, measure it: record the spot diameter at two distances and derive the growth. Do this before writing an irradiance value into a methods section, because the plane at which the number was taken is part of the number.
This is also why identical lamps in two labs produce different rates, a problem worth understanding before you blame the catalyst. The optical power may match while the illuminated area does not.
The four headline numbers are necessary but not sufficient; the omissions are where two otherwise similar units diverge in daily use. Look for the cooling method and its requirements, how lamp life is defined, the time needed to reach thermal equilibrium, and whether the quoted spectrum was measured at full power or at the reduced setting you plan to run.
If any of these is absent, request it in writing rather than inferring from the headline. A supplier who can answer these four questions precisely usually has the measurement data behind the rest of the sheet as well.
No. The 300 W refers to electrical input to the bulb. Delivered light is a separate figure — 50 W of total optical power on the PLS-SXE300E — and that second number is what sets irradiance at the reactor. Comparing two units by wattage alone compares their power supplies, not their beams.
Only if the measurement plane, spot size and spectrum match. Irradiance integrates everything the meter sees, so a reading taken at a different distance or through a different window is not the same quantity. Fix the plane, record the spot diameter, and state the spectral band in any comparison you publish.
Check three things: the interval covered, whether warm-up is excluded, and whether the value is drift or peak-to-peak variation. A figure with no interval attached is not a specification. Ask for a logged trace across a period at least as long as your own experiment.
