> I have a feeling its because professional production have big 300mm x
> 400mm size panels and the number of LEDs in one unit just makes it too
> large. It would have like 400 LEDs per side. Where as at present they
> just stick a few tubes in which can be replaced easily.
>
> Trev
No, sorry but that is not the reason. A typical exposure UV unit for industrial use can cost USD$10,000.00 and that is just the beginning prices. Although thousands of LEDs per side would be required, the number (and price) of them it is not significant in the industrial shops. The other main reason to avoid LEDs that I forgot to explain in another post is that the UV emission is very poor compared to fluorescent and mercury lamps. You could fix that getting closer the LEDs to the PCB board but that is not desirable in any way. To obtain real small traces and details the solution is to put the UV source and the PCB so far that is practical, so you would need very high ouput in the light source. Some professional UV units have the PCB and UV source separated more than 90 centimeters. However they use very high mercury-lamps and the exposure only needs a few seconds. Typical semi-professional UV exposure units (like MegaUK and so) made from fluorescent tubes also have narrow distances between the PCB and UV tubes, but that is a reason of compromise, trying to balance cost and performance.