S=Answer if you grow traditional soil
E-indoor
E-soil,
CSL-Soil type/brand - Wilko multi-purpose compost
E-Water source Filtered water from a Brita Filter
E-Age of plant 3 weeks
E-Lighting source and distance from plant 28w neutral white flourescent 3600K (2010 Lumens), 3-6 inches (try to keep around 4)
E-Air temperature (both day and night if you are running a dark period) ~80-90 degrees Fahrenheit/ ~28-32 degrees Celsius
E-Air % Relative humidity not much humidity
E-Lighting schedule 24/7
E-Type of ventilation your room has extractor and intake PC fans
TR-Did you pre-soak your media in pH corrected solution? soaked in pre-boiled (then cooled) sterile water

Are there any signs of pests on the undersides of the leaves? Use a magnifying glass or something to look really good. Look for specks that move, or other unidentified matter.
I will look with a magnifying glass in the morning, but looking very closely at all of the leaves and their undersides there is no sign of specs or anything moving.

Since you sprayed for critters the day before you noticed said spots, that could also be burn from spray.
I sprayed under a leaf very precisely hitting the pest squarely. The top of the leaves did not get any liquid. I am aware that liquids magnify the light and can burn plants. I didn't cover most of what is spotted with spray. Unless the pyrethrin burnt it and I didn't notice I sprayed more than I thought, but I was pretty sure it would be non-toxic to the plant.

Some more pics attached. Notice the specs let light through and you can see the real colour of the light. [pics are much enlarged if you click them again to see the pics on their own in new tab/window]

Thanks for your help.