Man that's a volatile question. Few questions stir emotions like that.now Let me tell you why... Simply put, some lights are better than others. Or at least perceived better. With purple lights this is seriously true. LED manufacturers lie about what their products provide. They aren't as bright as claimed, the foot print isnt anywhere close to reality, color spectrum is reported incorrectly, etc.
That being said there are some good purple lights out there. My peers are sick of hearing this but, i recently grew a 9 ounce plant with a Platinum P4. (Pic) its purple, it shows a white light because this LED also has some white CREE lights in it. I can turn the color LEDs off.
Now, this forum has a lot of COB LED light users in it. They are very powerful white LED lights. And apparently they are the bees knees. I dont know if they are or arent. If you upgrade, you might want to look at them.
Not so long ago LED users were getting shelled by the high pressure light guys because HP lights were the best light for growing pot... they held this title for decades. LEDs were expensive, and nowhere near as bright. COB users now seem to take the place of the HPS/MH guys. In there eyes purple lights are "old tech" and everyone should get on board the COB train. It doesnt matter who made your purple light, it sucks... they act just like the high pressure assholes of time past.
Don't even worry about it. Run what you got! YOU decide if it can grow good bud. It WILL grow pot. But will it be stringy with small buds? Will the light go into the plant and give good bud all the way down? Or will you have lime green underdeveloped bud in the lower parts of the plant? Is 2 plants too much for that? Probably. But, you could still have good bud on top, just make oil out of the rest of it.
This sight has some brilliant people on it. Ask good question dont embelish the truth, and dont worry about your light, this is what you have to work with. A friend on this site had this conversation just yesterday.
With a weak light there are techniques that could help you grow better bud... lollipoping your plant will do away with the lower stuff putting all the energy to the top. Or, SCRoG your plant ( I think this would work for you nicely). Screen of Green, this uses a net or trellis to pull your plant down so it grows flat, this allows the light to get down into the plant. Your light footprint probably isn't the greatest. So you don't want to grow you plants out too far. Don't veg too much. Your plant will stretch in the first few weeks of flower. You want that stretch to go up, not out. The tops will be allowed to poke through the net in flower.
Your light wont fill a room with blinding light, but you can get a good idea of the footprint of your light by measuring it at the a few distances. If you don't SCRoG. Make sure you can turn your pot... I assume you will use soil. There are so many things you can do to improve your situation. Go to Growweedeasy.com This place has a ton of info, on everything. It isn't a forum, its just info. I have spent hours there. You start at one place and follow links till your eyes bleed.
You've done good by joining this forum. Now grow something. I'm not super great at answering some of the crazier technical stuff, but i will try.
Cheers, looking forward to seeing what you come up with