There are currently 2 types of LED on the mainstream market, SMD3528 and SMD5050. The number is just the dimension for the SMD LED. 3528 is 3.5mm x 2.8mm, and 5050 is 5.0mm x 5.0mm. You will see the difference from the following picture. The width of circuit board for these two types of led tape are also different. SMD3528 has 8mm circuit board while SMD5050 has 10mm circuit board.
Although the size of 5050 is just a little bigger, it's 3 times more bright than 3528 becasue it's tri-chip LED. Each SMD3528 is emitting 5-6 lumens while 5050 is 15-16 lumens. Each SMD3528's working watt is 0.08 and SMD5050 is 0.24. All these two types of led tape are supplied in here inwww.ledsoptic.com , for best lighting effects we strongly recommend you use the SMD5050 LEDs.