Lumens is how much total light a bulb puts out. Foot-candles is how many lumens fall on a square foot.

That lamp puts out 20,000 lumens. Given that the lamp is roughly four square feet, you could achieve around 4,000 foot-candles by placing the lamp in very close contact to the plants. There are some losses in the reflector and you can't get every single lumen onto the plants. In practice you would use the lamp at least several inches away and possibly more, achieving perhaps 1,000-2,000 foot-candles over a larger area.

A lamp typically needs to be at least the height of the plant away from the top of the plant, otherwise you burn the top leaves and leave the bottom leaves too dark. Vandas are considered difficult to flower under artificial light because they require very intense light. You might be able to achieve it with this lamp. The next step up is an HID lamp, a 400W metal halide produces the same light as two of these Tek lamps.