How to Pick a Great Flat Screen TV, And Not Get Sucked In By Marketing Hype, Part 1: Brightness and contrast ratios

If you're looking at buying an affordable HDTV that will give you a good picture, our HDTV Buyer's Guide in the July 09 issue of PC Authority (it's the one onsale now) has expert tips on the features to look for, and our suggested "sweet spot" buy - a 42in beauty from Panasonic.

The article contains tips, tricks and secrets to buying an HDTV on a budget, including the following advice about that oft-misleading aspect of screen marketing, brightness and contrast:

Brightness and contrast figures have become so rubbery that some television manufacturers refuse to reveal them. Panel brightness is measured in candelas per square metre (cd/m2) and varies from 250 cd/m2 to up past 1000 cd/m2. LCDs panels are generally brighter than plasmas but anything over 400 cd/m2 should suffice in most lounge rooms.

Brightness is important if you'll be watching a lot of television in a brightly lit room, otherwise you should pay more attention to contrast.

Contrast refers to the ratio between black and white, for example 1000:1 means that whitest white is 1000 times brighter than the blackest black. Low contrast is one of the most common reasons for a poor picture, it means your blacks look grey and you lose fine detail in the shadows.

Plasmas generally offer greater contrast than LCD. Watch out for a form of voodoo mathematics used by LCD manufacturers known as ‘dynamic contrast'. In dark scenes it drops the brightness of the backlight to create blacker blacks, but obviously at the expense of the bright spots in the picture.

The difference between the blackest black in a movie's dark scenes and whitest white in the bright scenes is dynamic contrast, but you never see these extremes on the screen at the same time. The difference between the blackest black and whitest white in any one frame is the static or native contrast, which is the number worth paying attention to.

Also see our 5 tips for buying a digital TV set top box

And also see the lowdown on Freeview, and whether you should care

If you're new to Digital TV, or have yet to make the leap, start by reading Prepare yourself for Digital TV