Though these lamps are different in look, they actually have quite different modes of operation. See below for the differences:
Litespan
The light switch for the Litespan has two functions. It acts as both the on/off switch and the dimmer button.
1) To turn the lamp on or off, give it a firm but quick press, just for a second. Holding it down any longer than that will make the lamp think you're trying to dim it.
2) To dim it, hold down the button and the light will begin moving down through the different brightness levels, then back up when it reaches the bottom. Once you reach the level you like it at, you can just let go!
Litespan Slim
The light switch for the Litespan Slim has three functions. It acts as the on/off switch, the color temperature control, and the dimmer button.
1) On/Off: Give the power button a quick but firm press.
2) Color Temperature: When you turn the lamp on originally, it will come on at 6,000K Bright White. To cycle through the color temperatures, down to 4,500K Mid-White and 3,000K Warm-White, continue pressing the power button. It will turn off, and on again at the next lower color temperature. After warm white, the cycle begins again at the top
3) Dimming: Long press on the power button for a few moments, and it will begin to gradually dim. Keep holding the power button until the desired brightness is reached.