It's probably not too long until there are Kindle Touches with backlight support. At least the 5.1.0 software already is (partially?) prepared for it:
Code:
~/kindle-touch/java/classes$ LANG=C egrep -ri 'screen_?light' .
Binary file ./com/amazon/ebook/booklet/reader/impl/n.class matches
Binary file ./com/amazon/ebook/booklet/reader/utils/SwitchAppUtils$ScreenLightAction.class matches
Binary file ./com/amazon/ebook/booklet/reader/utils/g.class matches
Binary file ./com/amazon/agui/swing/resources/ComponentResources_it.class matches
Binary file ./com/amazon/agui/swing/resources/ComponentResources_en_GB.class matches
Binary file ./com/amazon/agui/swing/resources/ComponentResources_de.class matches
Binary file ./com/amazon/agui/swing/resources/ComponentResources.class matches
Binary file ./com/amazon/agui/swing/resources/ComponentResources_es.class matches
Binary file ./com/amazon/agui/swing/resources/ComponentResources_pt.class matches
Binary file ./com/amazon/agui/swing/resources/ComponentResources_fr.class matches
Binary file ./com/amazon/kindle/swing/actions/ScreenLightAction.class matches
Binary file ./com/amazon/kindle/swing/actions/ActionManager.class matches
Binary file ./com/amazon/kindle/swing/actions/ScreenLightAction$1.class matches
Binary file ./com/amazon/kindle/swing/actions/ScreenLightAction$Holder.class matches
Binary file ./com/amazon/kindle/control/util/q.class matches