I dont know is this is good place to post this question but it is part of my homework,
I was suppose to calculate how many LED chips should I use and get total lumens for 20W LED lamp. I have two types of chips, one is from cree and second one is from samsung. I need to use 700mA, 4000K, 80CRI.
first problem I get is how many lumens per watt is. From CREE datasheet page 12 I took this H4 which gives 970 lm, if voltage is 11.7 and current 700mA that is 8.19W and 970 lm / 8.19W is 118,43 lumens per watt. Is this correct calculation ?
and if I do the same for samsung datasheet from page 5 I took this chip M3 where is written 252 lm @ 700mA, is this number 252 lumens per watt or per chip ?
252 ln at @700mA means 252 lm at 700mA. To get the lm / W you need to know the forward voltage at 700 mA. Can you find that in the datasheet? Can you calculate the lm / W after you find that?
From datasheet forward voltage is 2.89V that is total power is 2.89*0.7 = 2.023W if I divide that 252lm/2.023W I have 124.57 lm/W meaning that 252lm from data sheet is lumens per led chip not per watt, is that correct ?
By the way, the original filament lamps were "half-watt lamps" and they produced about 25 lumens per input watt. In other words, a 100W filament lamp will give you 2500 lumens (modern filament lamps are slightly more efficient).