Photoshop/Illustrator difference in blend modes

Question

I have used photoshop for some time and am now trying to learn Illustrator (Both version CS5) I would like to know if there is a difference in the way the blend modes work between these two apps, specifically "Hard Light", I have included an example of the results of using the hard light blend mode on a white to black gradient square on a block of solid colour. The left image is what I would expect from Photoshop and on the right is what Illustrator displayed, is there anything I'm missing here?

Comparison of Photoshop and Illustrator Hard Light blend mode:

Answer 1

One important distinction is Illustrator's Document Color Mode.

Many blend modes will not appear as expected if you are creating or editing a CMYK document. RGB documents should be in line with Photoshop.

I would assume from your image that your Illustrator document is in CMYK mode.

You will find some blend modes simply will not yield what you expect in Illustrator CMYK. The basis for this is the backbone of the color coding. It's my understanding that Photoshop almost entirely uses LAB as it's basis for color decisions while Illustrator simply does not. Illustrator relies on color models based upon the Document Color Mode and, specifically in CMYK, can't "blend" colors in many cases the same way RGB or LAB can.

To be honest, I don't fully understand why Illustrator isn't more centered on LAB to allow more consistency across apps. But then there a million things which aren't consistent across Adobe apps and I don't understand why they aren't.