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Lynx_Arc said:
I don't have all the specs memorized but if you are trying to get even close to half that amount of light output you are going to have to go with high output luxeons or a rather large array of 5mm LEDs.... perhaps in the range of 100 or more. I would guess about 5 lux3 LEDs would be a start, part of which depends on what area you need to cover in light. The larger the area the more LEDs you will need to maintain intensity over the entire area.
What you need to look at is lumens output and start there.
A 40 watt bulb has I think about 450 lumens to start with, some of which is reflected,scattered elsewhere so I would guess about 2-300 lumens probably falls on the desk somewhere you can use it. Compare that to about 1-3 lumens for 5mm LEDs and about 15-25 lumens/watt on the luxeons and you can get the idea.
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I beg to differ. If you start with Lumens you are including all the light that never reaches the desk. On the other hand, if you start with measuring the light that falls on the desk (lux or cp) you will find that a single 1 watt LED may well match it. I have a 1 watt LED task light that produces as much light at 16 inches as a 250 watt halogen that's 4 foot above my work bench.
Daniel